College of Natural & Agricultural Sciences





Walter Ebeling

Chapter 9, part 1
Pests Attacking Man and His Pets

Summary | SPIDERS List | SCORPIONS List | ANTS List | Figure Captions

Part 2 | Part 3 | Part 4

Contents of Chapter, part 1

Many arthropds are pests because they bite, sting, or otherwise annoy humans and their pets. Some envenomate their victims, some transmit disease, and some, both. Others do not envenomate or transmit disease, but are merely annoying. All such pests are discussed in this chapter. Not included here are certain pests that are annoying and are also mechanical carriers of disease germs, such as the house fly and cockroach. These happen to be even more important in other ways (e.g., as food pests), and are more appropriately discussed under other chapter headings.

A distinction should be made between venomous (phanerotoxic) and poisonous (cryptotoxic) animals. The 2 terms are often used synonymously, but biologists generally consider venomous animals to be those that have a gland or group of highly specialized secretory cells, a venom duct (not always found), and a structure for delivering the venom. The venom apparatus is most commonly considered to be not only the stinger or fang, but also the associated gland and duct. Poisonous animals, as distinguished from venomous ones, have no venom apparatus, and usually poison their victims by being ingested (Russell, 1967b). There are at least 700 species of venomous arthropods, but only a few poisonous species. The latter would be hazardous to humans only if they were ingested. Among arthropods, only a few crustaceans are universally consumed. Members of a few primitive tribes eat insects, but they are well aware of the poisonous kinds. Therefore, poisonous arthropods are not discussed in this chapter.

Arthropods that attack humans and pets can be divided into 4 groups:

  1. species that inject their venom by means of fangs or stingers;
  2. species that inject their venom along with their saliva;
  3. species that are sources of allergenic emanations and inhalant allergies; and
  4. species that do not envenomate, but are merely pestiferous.

The indictment against all but the fourth group of arthropods is that each species has the ability either to envenomate its victims or cause allergic reactions, or both. Some of the same species are also vectors of disease organisms. Therefore, a discussion of envenomation, allergy, and disease transmission by arthropods is appropriate at this point. Venomous snakes are also included in this chapter because for practical purposes it is desirable to discuss all the principal venomers of the United States together.


Every year there are many thousands of arthropod and reptile envenomations in the United States, and during the period 1950 through 1959, they caused several hundred deaths. Hymenopterous insects were responsible for 229 of these deaths: bees, 124; wasps (yellowjackets and hornets), 101; and ants, 4. Spiders caused 65 deaths, and scorpions, 8. Snakes caused 138 deaths: rattlesnakes, 94; cottonmouth moccasins, 8; coral snakes, 2; snakes not native to the United States, 3; and unidentified snakes, 31. Thus, the hymenopterous insects caused about half of the deaths from venomous animals during the 10-year period. Bees and wasps were each responsible for more deaths than rattlesnakes, which caused 20.4% of the total number of deaths (Parrish, 1963).

People who succumb to envenomation by Hymenoptera usually die with alarming suddenness, often within 15 to 30 minutes. Of 208 deaths, 80% occurred in less than an hour. Only about 8 deaths resulted from overwhelming envenomation caused by hundreds of stings; the remainder resulted from insect allergy. This points up the importance of identifying and desensitizing allergic patients with appropriate insect antigens and instructing hypersensitive patients to carry insect allergy first-aid kits with them. In striking contrast to stings by Hymenoptera, only 11% of 54 victims of spider bite, for whom the period between bite and death was stated, died in the first 12 hours. Following the bite, 41% died in 12 to 48 hours, 26% from the third to the seventh day, and 22% after a week (Parrish, 1963).

Statistics also revealed that only 17% of snakebite victims died in less than 6 hours and 64% died in 6 to 48 hours after the bite. It usually requires several hours for the full toxic effects of the venom of American pit vipers to become evident, and there is a period of an hour or two following most snake bites when first aid and specific antivenin therapy may be used to best advantage. One of the most important causes of death from snake bite is said to be the failure to seek prompt and vigorous medical treatment (Parrish, 1963). Other things being equal, usually the smaller the victim, the greater the reaction to a given amount of venom.

The toxic effects of a venom result from the combined action of its components. However, additional effects may be attributed to metabolites formed when the venom components react with the constituents of the envenomated organism (Neumann and Habermann, 1956). The effects of autopharmacological substances such as histamine, bradykinin, and adeposine may be far more deleterious than those of the venom. In this chapter, the discussion of each arthropod will be accompanied by a discussion of the type of envenomation or allergic reaction produced by that species, whenever data are available.

Treatment of Arthropod Bites and Stings

Localized allergic reaction is evidenced by intense itching (pruritus), erythema, or scattered small urticarial papules. There are several effective anti-pruritus agents. Two are Calamine lotion and colloidal oatmeal bath, using Quaker Oats or a similar product. Antihistamine topical ointments such as tripelennamine hydrochloride 2% may be useful, but can cause sedation as well as allergic dermatitis (H. C. Spencer, correspondence). Pruritus may also be treated with an oral antihistamine and, on a physician's advice, by the local application of a combination steroid-analgesic preparation. Treatment should include thorough cleansing of the area around the wound to avoid secondary infection. Insects such as wasps that carry animal food or carrion to their nests are more likely to have infective stings than are bees. The above treatments may suffice, but further first-aid and medical measures and even hospitalization are occasionally required. If the bite or sting occurs on an extremity, one should avoid exercising it or placing pressure on it. Cold compresses may be applied to areas of localized swelling. A constriction bandage may be useful proximal to the sting site. It should not be applied so tightly as to cut off arterial pressure, and it should be loosened every 3 to 5 minutes. In cases of severe envenomation, as from the bite of the black widow spider, the sting of the deadly scorpion of Arizona (Centruroides sculpturatus Ewing), or multiple stings of bees and wasps, hospitalization may be required. Russell (1969) advised that all patients under 16 or over 60 years of age or with hypertensive heart disease receive antivenin following black widow spider envenomation.

For the reaction-prone person, an insect-sting kit is available that can be used during the period required to obtain a physician's help. The kit should contain a tuberculin syringe with a 26 gauge needle, an ampule of 1:1,000 aqueous epinephrine, and instructions for dosage and use. The recommended dose is 0.01 ml/kg of 1:1,000 solution subcutaneously. For oral medication, isoproterenol linguets, 10 or 15 mg, can be included (Zwemer & Handelman, 1971). An emergency kit should contain a constriction bandage, a sterile alcohol pad, suggestions for avoidance of hymenopterous insect stings, and Medic-Alert literature dealing with treatment.

Arthropod-Related Allergies

"Allergy" is thus defined by Pennak (1964) in the Collegiate Dictionary of Zoology:

Excessive sensitivity to a common substance such as pollen, many foods, natural oils, hair, dust, feathers, medicines, etc. The sensitivity is manifested in many ways, including hives, rash, asthmatic attacks, higher blood pressure, headaches, and nasal congestion; such symptoms are external manifestations of antigen antibody reactions, the antigens being substances mentioned above, and the antibodies being their specific antagonistic materials in the tissues and blood plasma.

Although "allergy" was originally meant to include all forms of human hypersensitivity, the term has later been generally applied to a group of diseases such as hay fever, asthma, urticaria, and eczema, all the consequences of an immune response to an exogenous factor. They characteristically involve production of an unusual kind of a reagin or skin-sensitizing antibody. This antibody reacts with the antigen or allergen to produce tissue damage. This phenomenon can be conveniently demonstrated by intradermal injections of various dilutions of the offending allergen, which result in a swelling or reddening at the site of injection. A clinically evident hypersensitivity having a basis of hereditary predisposition is called atopy. While allergic conditions develop spontaneously and only in some individuals, presumably from mild exposure to environmental agents, a more intense reaction, called anaphylaxis, requires intense artificial exposure, usually by injection. The allergic response can develop only in some individuals, but anaphylactic response can be obtained in all individuals of a species. An anaphylaxis-like reaction can occur in a person from an insect sting or following administration of drugs, foreign serum, vaccines, or from other allergenic exposures. Such a , response has been termed "anaphylactoid" to distinguish it from experimental anaphylaxis, although this distinction is not always made with precision in published reports (Arbesman, 1965; Shulman, 1967).

Man's sensitizing agents are made up of the various antibodies which a number of body tissues can produce to react with the foreign matter. The antibodies include specific immune substances against living viral or bacterial organisms or the foreign protein of allergens. The antibodies produced by the body may be of the wrong kind, produced in excessive amounts, or localized in the wrong places, or there may be combinations of these circumstances. In these situations, the antibodies go beyond the point of being purely defensive and become pathologic (Kern, 1962). Kern discussed in detail the relationship of sensitization to numerous environmental allergens that are ubiquitous, and in many cases are subtle and difficult to diagnose and define. Prolonged contact with the allergen may be required before symptoms become evident.

Allergies from Bites or Stings

Arthropods can be the sources of injectant or inhalant allergies. The arthropod may inject venom by means of

  1. a stinger in the abdomen, e.g., bees, wasps, ants, and scorpions; or
  2. by means of the mouthparts, e.g., sucking lice, bed bugs, reduviids, mosquitoes, gnats, fleas, spiders, ticks, and mites.

Allergic reaction may result from venoms secreted in venom glands or from salivary secretions that some arthropods inject subcutaneously.

The Insect Allergy Committee of the American Academy of Allergy studied over 3,000 completed questionnaires from persons experiencing allergic reactions to the stings of bees and wasps, of which 2,606 were recorded and analyzed (IAC, 1965). Of these, 13.3% reported only "local" reactions; 16.1% reported "slight general" reactions, in which there might be such symptoms as a few hives or itching beyond that which local swelling and pain might be expected to produce; 43.6% reported "moderate general" reactions; 24.2% reported life-threatening "severe general" reactions; and 2.8% reported "delayed" reactions, in which the time of onset of reactions was an hour or more after the sting. Symptoms indicating "severe general" reactions were dyspnea (difficult respiration), swelling in the throat, shock, and unconsciousness, the latter affecting 62.2% of the persons in the "severe general" reaction group. A sharp rise in the proportion of serious reactions in both sexes after age 30 suggested increasing sensitivity as the total number of stings received would mount over the years. A particularly disquieting finding was that responses to stings might be completely normal before the occurrence of a particular sting that produced a life-threatening allergic response.

An interesting aspect of the allergy problem is the fact that various biting or stinging arthropods often prefer to attack certain individuals in a family or group rather than others. The variations in the attractiveness of persons to insects result from differences related to temperature, moisture, age, sex, color, or physiological conditions of the person. Hormonal factors have been found to account for host selection by various species of mosquitoes (Brown, 1966) and fleas (Rothschild, 1965).

The clinical severity of reaction to insect bites and stings has been classified by Mueller (1959a, b), based on a study of 84 patients stung by bees or wasps, as follows:

  1. Slight General Reaction. Generalized urticaria (inflammation, wheals, itching, malaise and anxiety).
  2. General Reaction. A slight general reaction plus 2 or more of the following: generalized edema (swelling), constriction in chest, wheezing, abdominal pain, nausea and vomiting, or dizziness.
  3. Severe General Reaction. Any of the above reactions plus 2 or more of the following: dyspnea (difficulty in breathing), dysphagia (difficulty in swallowing), horseness or thickened speech, confusion, or feeling of impending disaster.
  4. Shock Reaction. Any of the above reactions plus 2 or more of the following: cyanosis (blue color because of insufficient oxygenation of blood), fall in blood pressure, collapse, incontinence (inability to restrain natural evacuations), and unconsciousness.

In the above investigation, there were a few patients in each group who reported a very rapid onset of symptoms after being bitten - as brief a period as 2 minutes. The average time reported declined from 24 minutes for group 1 to only 5 minutes for group 4.

Mueller reported that of the 84 patients studied, all of whom suffered at least a slight general reaction, 28 had personal histories of other allergies as well (close to the 30% found by the Insect Allergy Committee). There were 63 patients (75% that had family histories of allergy, 6 having histories of severe general reactions or shock reactions to insect stings. In 18 patients (21%) in which there was no family or personal history of other allergies, the reactions were generally mild, and there was relatively little skin sensitivity.

Repeated exposures to bites of a hematophagous insect generally result in changes in skin reactivity of the host that follow a definite sequence of 5 stages:

  1. no observable skin reactions during the period of induction of hypersensitivity;
  2. delayed skin reactions;
  3. immediate skin reactions followed by delayed reactions;
  4. immediate but no delayed reactions; and
  5. no reactivity (Feingold et al., 1968).

This sequence of stages of skin reactivity, as it applied to mosquito bites in an experiment on 25 human volunteers, is described on page 424.

Immunization or Desensitization

Mueller (1959b) presented extensive evidence that people suffering more than local reactions to hymenopterous insect stings could be successfully inoculated with mixed whole-insect extract of equal parts of bee, wasp, hornet, and yellowjacket ("Mixed Stinging-Insect Extract," Hollister-Stier Laboratories). The evidence seems to be overwhelming that the antigen that causes allergic reactions is present throughout the insect's body, independently of venom, but that the venom contains a small amount of this antigen (Hecht, 1929; Benson and Semenov, 1930; Ellis and Ahrens, 1932; Benson, 1936, 1939; Rockwell, 1952; E. Perlman, 1955; F. Perlman, 1962). At least 6 antigenic fractions are found in bee and wasp extracts. Some are species-specific, but others crossreact with those of other Hymenoptera (Arbesman et al., 1966). Patients generally are extremely poor observers concerning the true identity of the offending insect, and polyvalent therapy - longterm treatment with polyvalent bee and wasp antigens - is usually suggested (Torsney, 1968).

Mueller (1959a, b) concluded that testing a patient for sensitivity or treatment should always be started at a dilution of 1:100,000,000. Scratch testing was found to be an unreliable index to the degree of skin sensitivity. He stated that treatment is started at 0.05 ml of the dilution selected according to the patient's "initial positive test." Weekly increments in dosage are then given until 0.2 to 0.3 ml of a 1:100 dilution, the "maintenance dose," is reached, "or until a local reaction, larger than a silver dollar, is encountered twice with the same dose, after having dropped back and approached that dose a second time" (Mueller, 1959b). This is similar to one of the methods employed for pollen desensitization.

Mueller's patients were given their maintenance doses approximately every 4 weeks in the insect season and every 6 weeks through the winter for a period of 3 years. Subsequent stings were suffered by 40% of them. With 1 exception, none had resulting systemic symptoms (Mueller, 1959b). Patients treated by Frazier (1969) were given their maintenance doses about every 2 weeks in the insect season and every 3 weeks during the winter. He suggested that the mild-reaction patients should be discharged after 3 years of treatment, that the severe or shock-pattern reactors should be maintained in therapy indefinitely, but that time intervals between treatments should be increased where possible. Levine (1971) stated that the duration of immunotherapy should be at least 3 years, and perhaps should be continued indefinitely, but that there was no agreement on that point.

It may appear anomalous that repeated stings induce antibodies responsible for allergic reactions, and yet a large enough dose of the same venom (arrived at in gradual increments) will induce immunity. In the latter case, the "blocking antibody" differs from the allergic antibody in its molecular size, electric charge, capacity to withstand heat, and most importantly, in its effect on the host when in combination with its allergen (Frazier, 1969).

The questionnaires of the Insect Allergy Committee revealed an expectancy of progressively severe reactions in about 65% of persons not hyposensitized, whereas following hyposensitization, reactions to subsequent stings were reduced in about 90% of treated persons. The study showed that this protection by hyposensitization may be maintained for years, or may be lost in less than a year. The committee recommended hyposensitization for those persons who demonstrated any degree of systemic sensitivity following an insect sting (IAC, 1965).

Inhalant Allergies Attributable to Insects

The enormous numbers and wide distribution of insects and insect parts in the atmosphere give insects, like pollens, great potential as producers of allergic responses, particularly inhalant or respiratory allergies - that is, reactions similar to asthma. Small arthropods, and weak fliers in particular, may be carried for great distances from their breeding grounds by convection currents and upward in airstreams to as high as 10,000 ft (about 3,000 m). The dust and debris of decomposed arthropods become distributed in the same way, and these minute particles are important causes of inhalant allergies.

Inhalant allergy has long been known and can be readily demonstrated by skin tests. One of the earliest published reports on inhaled insect allergens was made by Wilson (1913), and concerned swarms of mayflies (Ephemerids). By placing a drop of a mixture of mayfly parts in 2 ml of sterile saline solution to one eye of a susceptible person, a marked conjunctival redness resembling that seen in allergy patients could be produced, whereas the other eye remained normal. Mayflies continue to be important sources of inhalant allergy, and caddisflies (Trichoptera) are other common sources, apparently first revealed by Parlato (1929). The hairs and wing fringes are easily dislodged and become windborne. Aphids, being extremely numerous and widely distributed, are also important sources of inhalant allergy. However, insects from most orders have been implicated. In an investigation of 222 allergy patients, 121 were sensitive to more than 1 insect, 25 were sensitive to only a single insect, and 76 were negative to all insects. Sensitivity to multiple insect antigens appeared to be the rule (Frazier, 1969).

Respiratory insect allergy has resulted from heavy occupational exposures. Examples are mushroom fly allergy in persons who grow mushrooms; beetle allergy in a museum curator; moth allergy in an entomologist in continuous contact with larvae and eggs of the range moth caterpillar; and also in an employee who had worked for 8 years with the larvae of the greater wax moth (bee moth), Galleria mellonella (L.) (Stevenson and Mathews, 1967). An employee of the then Federal Bureau of Entomology, after 2 years of employment, found that her hands and forearms itched severely when she worked with the Madeira cockroach, Leucophaea maderae (F). (Bernton and Brown, 1964). A man doing research on the control of dermestid beetles suffered severe allergenic reactions which became gradually more severe over a 2-year period (Okumura, 1967).

Thirteen crises of bronchial asthma were reported among workers at a sewage works in the Transvaal, South Africa, all the result of allergic response to the filter fly, Psychoda alternata. The inhalant allergen was demonstrated to be the dust resulting from the disintegration of the bodies of the flies. One individual was found to have no family history of allergy, and was not found sensitive to any of the more common causes of allergy, such as feathers, dusts, and pollens (Ordman, 1946).

Cross-Antigenicity. An interesting aspect of the problem of inhalant allergy has been the study of the cross-antigenicity between different types of insects. One antigen has been found to be common to a fly, a cockroach, and a cricket, another to a fly and a cockroach, and still another to a cricket and a cockroach (Pruzansky et al., 1958). Common antigenicity has also been found between crickets, grasshoppers, moths, and butterflies on the one hand and caddisflies on the other (Langlois et al., 1963).

Inhalant Allergy Attributable to Mites

The importance of house dust in inhalant or respiratory allergy was apparently first discussed by Kern (1921). He considered dust to be the most common cause of bronchial asthma. In 1922, mites were first mentioned as possible antigens in house dusts (Storm van Leeuwen, 1922). Inhalant allergy is attributable to many orders of arthropods, but in house dust certain species of mites appear to be the most frequent causes. Spieksma and Spieksma-Boezeman (1967) believed that no house dust allergen is formed in the absence of living mites, and proposed the name "house dust mite" for the leading European species, Dermatophagoides pteronyssinus (Trouessart). In Ohio, the predominant species of house dust mite is D. farinae Hughes (Mitchell et al., 1969), for which the common name "North American house dust mite" has been suggested (Wharton, 1970). In California, these 2 species are common, and may coexist in certain locations (Furumizo and Mulla, 1971). (See also the section on house dust mites at the end of this chapter.)


Many species of insects, particularly those that feed on or breed in excrement, are mechanical carriers of various "filth diseases," such as typhoid fever, cholera, and amoebiasis. The causal organisms may adhere to the tarsi, mouthparts, and other body parts of such insects, notably house flies and cockroaches, and may be deposited on food and on areas where food may be placed, as on sink tops, breadboards, or tables. The pathogenic organisms (bacteria, protozoa, helminthic ova, etc.) may also pass uninjured through the alimentary tract of the insect and be deposited on food via its excrement. Diseases like yaws (a spirochete infection) and certain eye infections such as "pinkeye" can also be transmitted mechanically by some species of flies. Some bacteria, such as anthrax (Bacillus anthracis) may be disseminated by flesh flies bred in carcasses of animals that have succumbed to the disease. The bacteria consumed by the fly larvae may survive through the pupal stage, and the adult flies may be infected and become highly mobile carriers of the disease. The piercing mouthparts of some insects like the horse flies (Tabanidae) may become contaminated by blood-inhabiting pathogenic organisms, and the insect may then spread the disease by simple mechanical means.

In all the foregoing cases of mechanical disease transmission, the pathogenic organisms undergo no developmental changes. Of much greater biological complexity and interest is transmission of pathogenic organisms that pass through cyclical changes and/or multiply in the body of the carrier. Huff (1931) suggested the following classifications for such "biological" transmissions:

  • I. Cyclo-Propagative. The organisms undergo cyclical change, and multiply.
  • II. Cyclo-Developmental. The organisms undergo cyclical change, but do not multiply.
  • III. Propagative. The organisms undergo no cyclical change, but they multiply.

An example of cyclo-propagative transmission is the transmission of the malarial parasite Plasmodium falciparum to man by anopheline mosquitoes which are then called vectors. Another example - is the transmission of the protozoan Babesia bigemina, the causal agent of "Texas fever" of cattle, by another arthropod vector, the Texas cattle tick, Boophilus annulatus (Say). An example of cyclo-developmental transmission is filariasis, in which the filarial worm is transmitted by certain mosquitoes. Probable examples of propagative transmission are the transmission of the bubonic plague bacillus, Yersinia pestis (= Pasteurella), which can multiply in the foregut of the flea, and the transmission of relapsing fever by ticks. Huff (1931) called attention to the fact that the most important types of transmission are I and III of the biological types, in which the disease organisms multiply within their arthropod hosts. Multiplication of the organism does not take place in mechanical transmission or in biological transmission type II.

It is probably an unfortunate circumstance that insect species with benign bites, and therefore those less likely to be shunned by humans, are the most potent vectors of disease. Among the Diptera, for example, Anopheles maculipennis, which does not inflict a painful bite, is a disease vector, whereas other species with painful bites, such as the field mosquito, Aedes dorsalis, and the stable fly, Stomoxys calcitrans, are seldom vectors of disease. If an insect is to be a successful vector, it appears to be generally necessary that it must be able to decrease the pain caused by its bite, as by local anesthesia.

Some arthropod vectors can transmit disease via their feces, such as flies transmitting plague, conenose bugs (Triatoma) transmitting Chagas' disease, or the mosquito Aedes aegypti transmitting yellow fever.

Disease organisms can also be transmitted via the egg of an infected arthropod (transovarian transmission). Examples are rickettsiae, bacteria, and spirochetes transmitted through the eggs of ticks that cause Rocky Mountain spotted fever, tularemia, and relapsing fever, respectively, and sand fly (pappataci) fever caused by the bites of the psychodid Phlebotomus papatasii reared from the eggs of infectious flies.

An important factor in the transmission of diseases by insect vectors is the fact that many wild animals serve as reservoirs for disease organisms. They suffer few or no ill effects from the diseases, but insect vectors can transmit the disease agents from these animals to man or domestic animals. An example is the rabbit as a reservoir for Rocky Mountain spotted fever and tularemia. Tularemia also exists in many other animals, among them meadow mice, ground squirrels, coyotes, sheep, and quail. Wild rats, particularly the roof rat, are reservoirs for human plague and typhus, for which fleas are the vectors. Care should be taken to avoid picking up fleas from wild animals.


This group of pests includes all the arthropods that cause the annual death toll in the United States, as discussed earlier in this chapter under "Envenomation": ants, wasps, bees, spiders, and scorpions. This is not meant to imply that other envenomating arthropods are not important. In fact, such pests as mosquitoes and gnats are probably of greater economic importance. Their bites are painful enough to cause great annoyance, and their numbers can be large enough to constitute the determining factor as to whether a district proposed for farming or residential development is inhabitable from a practical standpoint, or whether a proposed recreational area will be visited and enjoyed by the public. Mosquitoes and certain other insects that fall into the second group listed in the introductory part of this chapter, particularly fleas and lice, are also important disease vectors. Nevertheless, the pests that envenomate by injecting their venom should be recognized and understood, for their envenomation, while less common, can lead to serious consequences. As already stated, reptiles are included in this section so that all the important venomous animals can be discussed in one chapter.


Spider Species List

All spiders are predators, feeding primarily on insects and other arthropods. When feeding, spiders inject a predigestive liquid into the wounds of their prey and then suck up the digested food. They can survive for very long periods without food. Some South American brown spiders, Loxosceles laeta, have been kept alive for over 2 years with no food or water (M. Madon, personal communication). A concisely informative and well-illustrated (mostly in color) little book on spiders' and related arthropods is Spiders and Their Kin, by Levi et al. (1968). Illustrated keys for 44 of the families of spiders of the United States and Canada, as well as descriptions, illustrations, and other information on 398 species in 212 genera, are given by Kaston (1973).

Most spiders are nocturnal, unobtrusive, often feigning death when molested, and those frequenting human habitations will usually remain in undisturbed, dark, or dimly lighted, cool places. People are most likely to be bitten by spiders while cleaning out dark, neglected places such as basements, garages, or barns, or when gathering or cutting wood. Children may be bitten when playing in old, unused buildings. Bites may occur from spiders that crawl into a victim's clothing or shoes during the night or hide in bedding during the day.

Most spiders never attempt to bite without the greatest provocation, such as being squeezed or held. Many must be forced to bite when their venom is required for an experiment. However, only the larger spiders can penetrate the skin of a human with their fangs. Almost all spiders possess venom, but relatively few are dangerous to man. In the mainland United States, the black widow and the brown or violin spiders are the most dangerous, but moderate to severe symptoms can result from the bites of other species.

Biting Apparatus and Venoms

Spiders have an anterior pair of pedipalps and a pair of chelicerae with horny fangs at their tips (figure 207). Venom from modified salivary glands is injected through the hollow tips of the fangs (figure 208, D). It happens that the most common spiders (suborder Labidognatha) have their chelicerae (jaws) attached below the head. They are horizontal, open sideways, and oppose each other (figure 209, left). On the other hand, mygalomorphs (suborder Orthognatha), the trapdoor and hunting spiders, including the tarantulas, have chelicerae that are attached on the front of the head and move up and down, opening parallel with the long axis of the body (figure 209, right) (Levi et al., 1968).

Chemical and Pharmacological Properties of Spider Venoms

In a study made of the venoms of spiders in 4 genera, including Latrodectus, McCrone (1969) found that they contained many biologically active substances, ranging from compounds of relatively low molecular weight, such as gamma-aminobutyric acid, to those of relatively high molecular weight, such as enzymes and lethal polypeptides. The lethal effects of the venoms on both arthropods and man appear to result from the nonenzymatic peptides. Most of the other substances appear to influence primarily the distribution and action of the major lethal components.

Most venomologists feel that it has not yet been possible to classify spider venoms satisfactorily on the basis of their chemical or pharmacological properties. Such classifications as "neurotoxins," "hemotoxins," and "cardiotoxins" are misleading, and may give rise to unfortunate clinical decisions (Russell, 1967b). Black widow spider venom provokes a number of responses in humans, including hypertension, muscle spasms, weakness, and even paralysis. The bites of some spiders, such as Phidippus formosus (Peckham) (Salticidae), produce sharp pain, a wheal, and various local tissue reactions, including swelling and edema (Russell, 1970). The venom of Loxosceles sp. produces an ulcerative lesion which may become very large, but it is not yet clear whether the effects are caused directly by the venom or by some autopharmacological response provoked by the venom (F. E. Russell, correspondence).

Black Widow Spiders, (Latrodectus spp.) (Theridiidae)

In the United States, published reports of bites attributed to the black widow spider began to appear simultaneously from the southern states and from California beginning in 1889 (Herms et al., 1935). Black widow spiders (also known as combfooted spiders) are now the cause of the majority of the cases of serious arachnidism. When considered in relation to the total population of the country, black widow bites are infrequent.

The genus Latrodectus is cosmopolitan (Levi, 1958, 1959), and 5 species occur in the United States. The species are distinguished principally on the basis of differences in male genitalia. There are usually accompanying differences in gross characters, such as color and markings, but they cannot be relied upon to distinguish a species in all cases.

There are 2 species restricted to southern Florida, the "brown widow," L. geometricus C. L. Koch, and the "red widow," L. bishopi Kaston (McCrone and Levi, 1964). The brown widow prefers to live in human habitations, and is generally brownish, although there are also many black individuals. The cephalothorax of L. bishopi is usually bright orange, but is yellow or brick red in some specimens. The webs are not built under stones and debris, as with other species of Latrodectus, but are built 3 to more than 4 ft (about 1 to 1.5 m) from the ground, usually stretched between palmetto trees (Kaston, 1937).

Latrodectus mactans (F.) is the species most generally associated with the common name "black widow spider" in the United States. It occurs in the southern states, and its range overlaps that of the northern widow, L. variolus Walckenaer in the southern New England states, where the latter species is more common. L. variolus is also common throughout the northern states and Canada. Black widow spiders from the western United States and western Canada are L. hesperus Chamberlin and Ivie. The males of this species are usually light brown, whereas those of L. mactans and L. variolus are usually black (Kaston, 1968). Most investigators have found that the sex ratio of Latrodectus spp. is approximately 1:1. One investigator found that when the spiderlings were underfed, a higher percentage of males matured (Kaston, 1968, 1970).

Description. Female black widow spiders (plate VI,5, figure 208) are black, with a body about 12 mm long and a nearly globular abdomen 7.2 to 9.6 mm in diameter. The over-all length, including the legs, is 38 to 43 mm (Baerg, 1936). According to Kaston (1970), the body lengths are as follows:

Of the three species, Latrodectus mactans averages smallest for both sexes. Thirty-seven adult males ranged from 2.9 to 5.1 mm in length, with most between 3.2 and 4 mm; 52 females ranged from 5 to 13.5 mm, with most between 8 and 10 mm. Latrodectus variolus has the largest males, mostly between 5.5 and 6.5 mm, with a range for 34 specimens of 4.5 to 8.3 mm. Females of L. variolus are mostly 9 to 11 mm in length, with a range for 32 specimens of 7.4 to 13 mm. Latrodectus hesperus has the largest females, 59 specimens ranging from 8 to 15.5 mm, with most from 10.5 to 13 mm. Sixty-three males ranged from 3 to 6.5 mm, with most between 3.8 and 4.5 mm.

The great difference in sizes of males and females (figure 208) is even more apparent when weights are compared. Most males of L. hesperus weigh between 8 and 18 mg, while most of the adult females weigh between 120 and 400 mg (Kaston, 1970).

The black widow can be distinguished from all other spiders by the red hourglass figure on the underside of the abdomen (plate VI, 5). In many specimens, the pattern varies somewhat from the hourglass figure, or may be reduced in size, or in rare cases it may be absent. According to Sauer (1970), L. variolus has 2 red triangular marks ("split hourglass") instead of the typical hourglass of L. mactans.

Male black widows have relatively longer legs than the females, and have a lower and narrower abdomen that appears somewhat ellipsoidal (plate VI, 5, figure 208).

In addition the males are commonly more brightly colored. The mature male resembles the fifth-instar female in body markings, but it is much smaller. The male also possesses the ventral red hourglass figure on the abdomen. Dorsally, the pattern is variable, but usually consists of a median row of red spots with white lines radiating out to the sides. The pedipalps are large and bulbous. The venom sac of the male is small, and is not functional after he matures.

Kaston (1968) pointed out that many specimens of the female black widow spider were noted to be purplish brown, chestnut brown, or light chocolate brown rather than black, and that they might undergo changes from one of these colors to another.

The Black Widow's Web

The web of the black widow spider is an irregular mesh in which the spider hangs in an inverted position (figure 208). It is used to ensnare insects and other small prey, and consists of a network of silken strands that are stronger than those of most spiders. There is usually a small, central pocket or retreat to which the spider resorts when frightened. The prey sets up vibrations in the thread that announce its presence to the spider. Baerg (1936) noted that when black widow spiders lived under stones, they had relatively small webs or none at all. Presumably, this particular ecological niche attracts plenty of victims, and the spider is aware of their presence when they contact the few threads spun around her body. The webs usually found in old barns, sheds, crawl spaces under houses, or in little-used parts of garages and basements are likely to be about 30 cm across and equally as high, but they can sometimes be larger. Kaston (1970) described a web of Latrodectus hesperus in an unused wooden shed that had a "catching portion" about 30 in. (75 cm) above the ground level, with threads extending to a retreat in the rafters about 12 ft (4 m) above the ground. The female avoids light, and during the day may stay under a piece of overhanging board or a clod of earth, or may remain back in her retreat. She may move out over her snare at night and assume a position several inches in front of the overhang of the object under which she was hiding.

Life Cycle. The eggs of black widow spiders are deposited in silken egg sacs (figure 210) that can be constructed by the female in 1 to 3 hours. According to Kaston (1970), the egg sacs of Latrodectus mactans average about 9.5 mm in diameter, are spherical, with a conspicuous nipple on top, and gray. The egg sacs of L. hesperus are about 1.1 cm in diameter, pyriform, and tan, and those of L. variolus are 1.2 cm in diameter, pyriform, and gray. Kaston observed as many as 6 egg sacs per female for L. variolus, as many as 10 for L. mactans, and as many as 21 for L. hesperus. The mean number of eggs in 185 sacs of L. mactans was 255, and for 464 sacs of L. hesperus it was 196. The outer covering of the egg sac is tough and closely woven, differing in this respect from that of the brown recluse spider, which has an outer covering of loose threads. Baerg (1936) frequently saw a female with 4 egg sacs, and once saw one with 6. Under laboratory conditions, they have been observed to construct as many as 9 sacs in succession.

An egg sac will occasionally be found to be empty. The eggs of all 3 species are usually creamy white to yellow. The incubation period was noted to be 14 to 30 days in California by Herms et al. (1935), and from 15 to 21 or 30 days in Kansas by Lawson (1933). In the laboratory at 25 °C (77 °F), Kaston (1970) found the average incubation period (in days) to be 13.4 +2.0 for L. variolus 14.2 +1.4 for L. mactans, and 14.6 +2.0 for L. hesperus.

The Spiderlings. When newly hatched, the tiny spiders undergo their first molt inside the egg sac about 3 or 4 days after hatching. They emerge from the sac in about 26 to 30 days after oviposition. There is usually a single emergence hole about 1 mm in diameter cut out by 1 or 2 spiderlings, but sometimes there may be 2, and rarely 3 holes (Kaston, 1970). The newly hatched spiders are pale reddish brown, with light and dark stripes on the abdomens and legs. They move about in the vicinity of the nest for several weeks, and many are destroyed by other spiders in search of prey, including their own kind. The mother will not eat them, even when she is starved.

Spiderlings are poisonous (when ingested) before emerging from the egg sac and until they are about 18 days old, after which the poison disappears. It is said to be "dramatically different" from the venom of the adult spider. Extracts of the eggs and spiderlings, when given to cats, caused a precipitous and often fatal hypotension, whereas the venom of the adults caused an acute and persistent hypertension (Buffkin et al., 1971).

Description of Instars. There may be as many as 9 instars, but the spiders can mature in fewer instars. In a study of a total of 544 spiders, including males and females of 2 species, Kaston (1970) found that the mean periods required for them to become mature varied as follows: Males of L. hesperus matured in 4 to 7 instars in 62 to 151 days. The periods required for maturity increased with increasing numbers of instars. Females matured in 6 to 9 instars in 137 to 242 days. Latrodectus mactans males matured after 4 to 7 instars in 54 to 88 days, and females after 6 to 8 instars in 112 to 140 days. Only 1 male had 8 instars (in 166 days), and only 1 female had 9 (in 107 days).

Kaston (1970) described each instar of the 3 species of black widows. These vary greatly in appearance from one another and from the adults, and this in part accounts for the long list of synonyms. Figure 211 shows some dorsal and ventral patterns of late instars of L. hesperus. Kaston described all the instars in detail, but space permits only the inclusion of his description of the sixth instar (figure 211, A, B, C), which could be the penultimate (next to last) one, for females can become mature in the seventh, eighth, or ninth instar.


The darker specimens show more pigment on the carapace and have the dark areas more extensive than previously. There remains on the sternum only a narrow central light band. On the legs the dark areas have increased in size.

The abdominal dorsum is mostly covered with dark pigment now, with the only light areas reduced to a basal transverse band, a row of spots along the midline, and 2 pairs of diagonal stripes extending down the sides to the rear. These latter are the areas that had previously been narrow. Each of the light spots along the midline encloses a reddish spot. The hourglass mark is becoming more constricted at the middle and has more red pigment.

Some individuals, showing a more or less similar arrangement of spots, have the pigmented areas lighter. Also, the light diagonal bands extend farther down on the sides, and the dorsal spots are more orange than red.

The figure shows that the dorsal marking of the penultimate instar of the Latrodectus hesperus male is remarkably similar to that of the fifth instar female. There is subsequently little if any difference in the markings in the male, even if it has as many as 7 instars; they continue to resemble females of the "light variety" of L. hesperus in the fifth or sixth instars.

Longevity of Adults. In California, most of the spiders overwinter as immature individuals, maturing sometime in the spring (Herms et al., 1935). In Arkansas, the young spiders generally mature in May or June (nearly a year from egg to adult), and begin to die in considerable numbers in late July. They can be kept alive in the laboratory for 2 years or more (Baerg, 1936). The maximum number of days of survival of males after maturity was found by Kaston (1970) to be as follows: Latrodectus mactans, 127; L. variolus, 155; and L. hesperus, 196. The corresponding figures for females were: L. mactans, 849; L. variolus, 822; and L. hesperus, 952. Spiders are known for their ability to live for long periods without food. Kaston kept 37 black widow females without food for periods ranging from 36 to 193 days, with an average of 89.3 days.

Habits. In the laboratory, the reaction of spiderlings to a fan-produced breeze was to climb upon whatever supports were provided, to distances at which the air currents were most suitable, and to spin webs and let themselves float like kites, the silk functioning as the tail of the kite. If the wind is in the right direction, a house may be showered with spiderlings, and many will find suitable locations, establish their webs, and grow to maturity. "Ballooning" of black widow spiderlings provides for general distribution of the species in upland, lowland, wild, and rural areas, towns, and cities (Baerg, 1936).

Outdoors, black widow spiders commonly live under and among stones, under pieces of wood, in hollow stumps, in rodent burrows, and less commonly among the leaves of plants and in low shrubbery. Sometimes the black widow becomes so abundant in the vines of such crops as tomatoes and grapes that harvesting may be hazardous and gloves should be worn. However, these spiders are most commonly encountered in dry and sheltered man-made structures, such as outdoor privies, barns, henhouses, garages, cellars, furniture, in water-, gas-, and light-meter boxes, and in woodpiles or piles of rubbish. One often sees the egg sacs of the black widow spider, but not the spider itself, when crawling about extensively under a house, as when inspecting for termites (figure 72, chapter 5). There, the black widows are preyed upon by ground beetles, scorpions, wolf spiders (Lycosidae), funnelweb weavers (Agelenidae), and mud daubers, as well as by others of their own kind. However, their predators may sometimes themselves be vanquished in the encounters and, along with other small arthropods, may serve as food for the black widow.

According to Sauer (1970), the northern widow may be found throughout the lower peninsula of Michigan, where it "occurs in marginal land where the vegetation is rather sparse, often hiding in old stumps, hollow logs, under fallen fenceposts, in abandoned animal burrows or piles of dead tree branches, and other debris. It prefers these outdoor situations to buildings, whereas the black widow of the southern United States can be found in both habitats."

Natural Enemies. A dipterous egg predator of black widows, Pseudogaurax signatus (Loew) (Chloropidae), has a sparse distribution. The most common hymenopterous parasite is a scelionid, Baeus latrodecti Dozier, reported from egg sacs by Pierce (1942). Other hymenopterous egg parasites are a eulophid and a Eurytoma.

Another spider, Steatoda grossa (C. L. Koch) (figure 212), in the same family (Theridiidae) as the black widow, has been observed feeding on the latter. This species is mentioned in chapter 6 as one of the predators of cockroaches. Other black widow predators are species of Mimetus, the pirate spider. The most widespread and possibly the most effective predator is the blue burglar wasp, Chalybion californicum (Saussure). It will provision its cells with black widows in preference to other spiders. The San Diego alligator lizard has also been found to be an effective predator (Kaston, 1970).

The Bite of the Black Widow

The bite of the black widow spider is not always felt, and often there is little evidence of a lesion. There is usually a slight local swelling and redness, and 2 tiny red spots may appear. It is important for a physician to take note of these spots, for they indicate the 2 entrance points of the spider's fangs. A single entry mark might indicate the bite of a conenose bug or some other insect, and the administration of an antitoxin for black widow spider venom would not only be useless but could actually be harmful. Pain is felt almost immediately, reaches its maximum in 1 to 3 hours, and continues for 12 to 48 hours, gradually subsiding. In severe cases, there is rigidity and spasm of most of the larger muscles, particularly of the abdomen, which becomes "boardlike." There is a rise in body temperature, increased blood pressure, profuse perspiration, and a tendency to nausea. Other symptoms, such as chills, urinary retention, constipation, hyperactive reflexes, and a burning sensation of the skin, are frequently reported.

The black widow can control the amount of venom ejected from her venom glands. For example, when attacking insects on which she feeds, she injects a dose commensurate with the size of the victim. When biting a human being, she attempts to inject her entire supply of venom. The amount of venom held in her sac at the time of the bite depends on how recently she has used her fangs. These do not always break through tough skin, since they are less than a millimeter in length. If she drops on the hand or arm, she should be brushed off rather than swatted, in order to avoid pushing the fangs into the skin. It is fortunate that the black widow can inject only a relatively small amount of venom, for the venom is 15 times more powerful than that of a rattlesnake. Nevertheless, the bite of a rattlesnake is considered to be more dangerous because of the much greater dose of venom injected. There is about 15 to 25% mortality of persons bitten by rattlesnakes. According to Wingo (1960), there is less than 10% mortality of persons bitten by black widow spiders.

The black widow will attack any object that touches her web, but she feeds mainly on insects. Insect remains are generally not seen on the web, suggesting that the black widow may remove them from the web sooner than do other spider species.

The web of the black widow is very strong, and has been known to snare animals as large as lizards and mice (Kaston, 1970).

Approximately 300 spider bites, of all kinds, are reported to physicians in southern California each year, but fewer than 5 persons per year, usually children, die from spider venom poisoning (Russell, 1969). Yet a child weighing 30 pounds or less would have only about a 50 per cent chance of surviving if he received the entire quantity of a black widow spider's venom and were given no medical attention (F. E. Russell, personal communication). The physical and mental condition of the victim of a black widow spider can, of course, have a great effect on the seriousness of the reaction. However, the bite of a black widow spider need never be fatal if treated promptly by a physician.

Brown Recluse Spider, Loxosceles reclusa Gertsch and Mulaik (Loxoscelidae)

Montgomery (1908) found that the brown recluse spider was common in its silken hibernaculae under stones in a Texas area during winter. It was described later by Gertsch and Mulaik (1940). What appeared to be its first proven bite occurred in Kansas in 1928 (Schmauss, 1929), but not until 1957 was there circumstantial evidence that associated this species with the typical sloughing bites that physicians had been seeing (Atkins et al., 1957). The following year, the sequence of results from the bite on experimental animals was recorded (Atkins et al., 1958).

The brown recluse occurs in the United States in the southern parts of Ohio, Indiana, and Illinois, in Missouri, Kansas, and parts of Nebraska, and southward to the Gulf of Mexico. This species and its near relatives may now be included with the black widows (Latrodectus spp.) as being among the few spiders in the country for which it can be said that their bites, although uncommon, are causes for justifiable concern.

Description. The adult females (plate VI, 6; figure 213) vary from 7 to 12 mm in length, averaging about 9 mm, and the males are a little smaller, averaging about 8 mm (Gertsch, 1958). The males are readily distinguished by their bulbous pedipalps. The legs of L. reclusa are long, and are covered with minute brown hairs, but appear almost bare to the unaided eye. The body color varies from light fawn to dark brown. Recently molted individuals have a lighter color. They have 6 eyes, arranged in pairs in a semicircle unlike most spiders, which generally have 8 eyes. Immediately behind the eyes is a violinshaped marking on the anterior portion of the cephalothorax, with the neck of the violin pointing backward and narrowing down to a center line extending almost to the abdomen. This is a conspicuous mark, and has resulted in this and related species being called "violin spiders." The immature stages closely resemble the adults except for size and generally having a slightly lighter color.

The Web. The medium-sized, irregular web is made up of a maze of very viscid threads that extend in all directions without a definite pattern. It has been described as an off-white or grayish, nondescript, "cobweb-type" webbing. The web is not used specifically for trapping insects and other prey, but mostly as a retreat for the spider. In its outdoor habitat, the brown recluse spider spins a tube of thick silk as a retreat in winter. Likewise, in the laboratory the spider often constructs a retreat of loose silk in 1 part of its web (Hite et al., 1966).

Life Cycle. The egg sac consists of a circular base of densely woven silk threads upon which the eggs are laid. The female then spins a dense cover over the eggs. After resting, she then spins a more loose and flocculent cover. The completed egg sac is white, flat beneath, and convex above. It averages 3.7 mm in height and 17 mm in diameter. From 1 to 5 egg sacs are produced. The young emerge from the eggs in 25 to 39 days (a mean of 32.6) (Hite et al., 1966).

In a laboratory, egg production varied from 31 to 300 per female. From 146 egg cases containing 7,374 eggs, 3,576 young emerged. Sometimes females fed on eggs, and sometimes the young from a preceding egg sac fed on later eggs. There were 8 instars, and the period from egg to adult varied from 266 to 444 days, with a mean of 336 days. Males lived an average of 543 days, and females, 628 days (Hite et al., 1966). On the other hand, 30 females, assumed to be about 540 days old when they were collected, were kept at normal room temperature in summer and a near-natural environment in winter. They were reared another 880 days, and were then in their fifth overwintering hibernacula (Horner and Stewart, 1967).

In Arkansas and surrounding states, mating occurs from early February to early October, the most active period being in June and July. No egg-laying was observed in October to January, inclusive (Glick, 1969).

The Brown Recluse's Habitat. Hite et al. (1966) recorded the location of 298 brown recluse spiders, collected in homes in Arkansas, as follows: in boxes, 156; among papers, 39; in bedrooms, 29; attics, 22; halls, 14; utility rooms, 11; kitchens, 11; livingrooms, 5; bathrooms, 4; front porch's, 3; window wells, 2; cellar, 1; and basement, 1. In school buildings, among 74 spiders, 45 were found in schoolrooms, 26 in basements, 2 in attics, and 1 in a storeroom. In other sites, among 58 spiders, 21 were found in the loft of a feed mill, 11 in a broiler-house storeroom, 10 in storehouses, 8 in cabinet shops, 6 in garages, and 2 in sheds. Outdoors, of 196 spiders collected, 158 were found under rocks, 34 under piles of inner tubes, 2 under houses, and 2 under bark.

In homes the brown recluse spider may be found in old clothes, on the undersides of tables and chairs, behind baseboards and door casings, or in corners and crevices. It usually runs for cover when disturbed, accounting for its common name. People are most likely to be bitten when putting on old clothes or shoes that may not have been worn for long periods, or by rolling on the spider in bed.

Symptoms of the Brown Recluse's Bite

Venom was extracted from 3,000 Loxosceles reclusa spiders by electrical shocks and was collected in microcapillary tubes. The quantity of venom collected per spider ranged from 0.25 to 0.62 ul, with an average of 0.36 ul. Male spiders gave less than half as much venom as females, but it had the same toxic properties (Morgan, 1969). Both sexes are able to inflict venomous bites to mammals. The following is a description in nonmedical terms of the reaction to the bite in man, as quoted from Wingo (1960):

The typical reaction in man following a bite by the brown recluse is necrosis (killed tissue) at the site of the bite. The victim may not be aware of being bitten for 2 or 3 hours, or a painful reaction may occur immediately. A stinging sensation is usually followed by intense pain. A small blister usually rises, and a large area around the bite becomes congested and swollen. The patient may become restless, feverish, and have difficulty in sleeping. The local pain is frequently quite intense, and the area surrounding the bite remains congested and hard to touch for some time. The tissue affected locally by the venom is killed and gradually sloughs away, exposing the underlying muscles. The edges of the wound thicken and are raised, while the central area is filled by dense scar tissue. Healing takes place quite slowly, and may take 6 to 8 weeks. The end result is a sunken scar which has been described as resembling "a hole punched or scooped from the body." Scars ranging from the size of a penny to half-dollar have been reported.

The necrotic condition described above is typical of all bites of the brown recluse. However, in some cases a general systemic reaction has also occurred. In one case, the patient broke out with a rash resembling that of scarlet fever. In another case, the kidneys were apparently affected, causing bloody urine to be passed. These systemic disturbances probably occur infrequently, and are the results of a "full" bite (i.e., the injection of a maximum amount of venom) or extreme sensitivity to the venom. This general reaction to the bite of the brown reduse is certainly a serious condition, and hospitalization of the patient is usually required. Those in poor general physical condition, young children, and older people are more apt to be affected seriously by the bite of the brown reduse.

The principal injury inflicted by the brown recluse is the severe tissue damage, which is deep and heals slowly. Death rarely results from the bite of this spider. Successful therapy and prevention of local necrosis and severe systemic toxicity depend on early recognition of the symptoms followed by the application of appropriate, vigorous therapy (Bolton, 1970). Good results have been obtained with a course of treatment employing certain corticosteroids, but treatment initiated 48 hours or more after the bite is unlikely to have any effect (Dillaha et al., 1964). figure 214 shows the healing sequence of a lesion resulting from the bite of a brown recluse spider that was first photographed on June 24, 1968, about 48 hours after the bite occurred, and for which photographs were made at intervals until August 23, 1968, a period of 58 days. Debridement (surgical removal of lacerated, devitalized, or contaminated tissue) was done at necessary intervals as the tissue sloughed off. A bleb (small blister) recurred at the initial site of the bite almost 6 weeks following the original blister, and this was found to be typical of the lesions observed (Glick, 1969). Before 1968, there had been at least 126 cases of this type of necrotic spider bite in the United States (and 6 deaths), and about 400 cases in South America (and at least 35 deaths) (Gorham, 1968).

Some Relatives of the Brown Recluse, Native and Introduced

There are about 50 species of Loxosceles in the Western Hemisphere, and according to W. J. Gertsch (correspondence), identification depends almost exclusively on a study of the genitalia. In immature stages where the female genital receptacles are not present, it is virtually impossible to identify the specimens. Any species within the United States can be distinguished by superficial observation, particularly in view of the relatively small overlap in geographical ranges. There are several other Loxosceles spiders in the country that are similar in size, shape, and coloration to L. reclusa, but their violin-shaped markings are sometimes less distinct, and may be somewhat faint in some species.

Loxosceles unicolor Keyserling

This is the only species of Loxosceles that is indigenous to California. It is distributed in parts of California, Arizona, New Mexico, Nevada, Utah, and Texas, in Mexico at least to southern Sonora, and in Baja California (Gertsch, 1958). Specimens collected by Russell et al. (1969) were generally found near human habitations, from beneath ground cover such as lumber, rocks, or debris, and also inside houses. These chiefly nocturnal spiders live a solitary type of life and move quickly when attempting to escape.

Description. The females (plate VI, 6) are from 6 to 9 mm long and average about 7.5 mm (Gertsch, 1958; Russell et al., 1969)' The males are slightly smaller. Thus, L. unicolor has a smaller body than L. reclusa, but has longer legs. According to Russell and associates, L. unicolor is light brown, sometimes with a shading toward beige or yellow. Ennik (1971) found that the color and to some extent the size of the abdomen of L. unicolor depended on the quality and kind of prey it ate. Drosophila flies as food caused their abdomens to turn orange-red, but house flies caused them to turn gray. Grasshopper nymphs caused a light green and German cockroaches a violet color. The "violin" on the cephalothorax of L. unicolor is not so distinct as in L. reclusa. Males can be recognized in the penultimate stage by the enlargement of the pedipalpal tarsus. Females can be recognized in the same stage by the reddish color of the tibiae and tarsi of the pedipalps and of the genital furrow border (Ennik, 1971).

Life Cycle. Spiderlings hatch 15 to 19 days after oviposition. Then follows the first post-embryo, confined in a membranous sac; a second post-embryo, when the sac is ruptured; and the first molt 11 to 16 days later. Although the spiders may mature in any stadium after the sixth molt, the majority of males become adult in the seventh and eighth molts, and the majority of females in the sixth and seventh molts. The developmental periods of the sexes were found to be as follows: males, 290 to 680 days (mean of 464); females, 276 to 562 days (mean of 399) (Ennik, 1971).

Bite Symptoms. Loxosceles unicolor can inflict a bite that causes pain, bleb formation, erythema, and necrosis leading to ulceration, but the skin responses and systemic changes are not usually so severe as those caused by L. reclusa. Apparently, only 3 cases of necrotic arachnidism in which L. unicolor was positively identified as the cause have come to the attention of medical authorities in California. However, bites by L. unicolor appear to be more common than had formerly been expected; descriptions of some.of the lesions reported by physicians appear to be similar to some that have been definitely connected with this spider (Russell et al., 1969).

Arizona recluse, Loxosceles arizonica Gertsch and Mulaik

This species occurs in Arizona, New Mexico, western Texas, and southward into Mexico from Coahuila to Baja California. The females are 6 to 10 mm in length, averaging 8 mm (Gertsch, 1958). The males are slightly smaller. These spiders have been described as being darker in color than L. unicolor, but Russell et al. (1969) found no such difference in specimens they examined. Specimens from arid regions tended to be paler. The violin markings were always distinct (figure 215).

As with L. unicolor, L. arizonica can now be considered to produce lesions. Many of the lesions that have been recorded as "necrotic arachnidism" during the past several years in areas where L. arizonica is indigenous have probably been caused by that spider. Experimental envenomation of hairless mice by L. arizonica and L. devia (see below) has been demonstrated (Cutler and Cutler, 1971).

Texas recluse, Loxosceles devia Gertsch and Mulaik

This species ranges through southern Texas and the adjacent states of eastern Mexico. The area of distribution of L. reclusa slightly overlaps that of L. devia in Texas. The latter is the smaller of the 2 species, with both males and females averaging about 7.5 mm in length. It also has a paler carapace, and the typical dorsal pattern ("violin" marking) of L. reclusa is mostly lacking (Gertsch,1958).

Chilean recluse, Loxosceles laeta (Nicolet)

This spider has been associated with the "gangrenous spot" syndrome in Chile since at least as early as 1937 (Macchiavello, 1937). The lesion is similar to the one produced by L. reclusa. An antivenin has been prepared against L. laeta for the treatment of both the cutaneous lesions and the systemic manifestations of that spider's toxin, but at least by May, 1970, the antivenin was not available in the United States, possibly because it had been found to be unsuccessful against the toxin of L. reclusa (Bolton, 1970).

Beginning in 1960, L. laeta was found in basement areas in a museum and in a terrarium at Harvard University, Cambridge, Massachusetts (Levi and Spielman, 1964). Eventually, more than 50 spiders were collected and many more were observed. One building occupant stated that the spiders had been there for at least 20 years. A further observation was made that it had been about 20 years since firebrats (Thermobia domestica) had had to be controlled in the infested area. Loxosceles laeta apparently did not spread beyond the infestation at Harvard, and is not known to occur elsewhere in the New England states (Spielman and Levi, 1970).

In 1969, this species was found in Sierra Madre, California, a suburb of Los Angeles, where about 190 spiders were collected in an 8-block area. The infestation was believed to be at least 2 years old (Hawthorne, 1969; Waldron, 1969a). During the same year, an even greater area of infestation and greater numbers of spiders were found 11 miles (18 km) away, in the city of Alhambra. It seemed apparent that the spiders had been in the Alhambra area 5 years or longer. The extreme shyness of Loxosceles laeta and its rapid movements may have helped to keep it from being detected sooner (Waldron, 1969a).

Description. Loxosceles laeta is similar to L. reclusa in appearance. It is the largest species in the genus. The living specimens (plate VI, 7) are tawny to brown or blackish, and the dead specimens generally seen in collections are yellow to reddish brown. The cephalothorax and legs are more reddish than in L. reclusa. The "violin" on the cephalothorax is not quite so conspicuous as in L. reclusa, but is readilv discernible. W. J. Gertsch (correspondence) pointed out that the palpal tarsus of the male L. laeta is longer than wide, whereas in L. reclusa, it is wider than long. In laeta, the palpal tibia is narrow, and in reclusa, it is shorter and broader. In laeta females, the fourth leg is longer than the others, while in reclusa, the second leg is longest in both sexes. The palpi of the laeta males have a distinctive form. Of 5,449 L. laeta collected in houses in central Chile, the ratio of males to females was 1:8 (Schenone et al., 1970).

Habitat. In the Harvard infestation, the spiders were usually seen on floors and baseboards, only rarely on desks and tables, and never on walls. It was noted that L. laeta could become very numerous itself, while appearing virtually to eliminate all other arthropods. Webs sometimes reaching 30 cm in diameter were typically found in corners, as noted by Waldron (1969a) in the California intestation. This was in keeping with a common name for L. laeta in South America, ara–a de los rincones (corner spider). The loosely woven egg case, containing about 50 large, white eggs, was always placed in a dense portion of the multilayered web. Males were frequently found without webs. Lindane proved to be the best insecticide in control tests at Harvard.

Attempts to Provoke Biting. Six females of L. laeta were confined to a guinea pig's flank, and although they were pressed against it and provoked, none bit the animal (Levi and Spielman, 1964). This was contrary to tests with L.reclusa in Arkansas, in which the spider could easily be provoked to bite under similar conditions (Atkins et al., 1958).

In another similar experiment L. laeta was provoked to bite rabbits. The reactions of the rabbits to the bites of Loxosceles reclusa, L. laeta, and L. rufescens (mentioned following) were similar, and the reactions to males and females of the 3 species were also similar. The spiders probably did not usually deposit all their venom in a single bite; a second bite frequently caused a lesion at least half the size of the first (Smith and Micks, 1968).

Mediterranean recluse, Loxosceles rufescens (Dufour)

This species, apparently imported from Europe, now occurs in a number of localities, from New York to Illinois and throughout the southeastern states. It is similar to our. indigenous species in general appearance. The female is 7.5 mm long and the male, 7 mm (Kaston, 1973).

Chiracanthium inclusum Hentz (Clubionidae)

This is a pale-yellow spider, with a body about 5 to 6 mm long, that is widely distributed throughout North and South America and frequently appears in houses.

In California, a man awakened by a sharp, penetrating pain below the outer margin of the right eye found that he had been bitten by an immature male of C. inclusum. Cold compresses applied over the area of the bite for an hour and taking 2 grams of aspirin over a 4-hour period did not alleviate the pain. Within 3 hours after the bite, a throbbing pain had spread over the cheek; after 7 hours, the pain was still intense, but seemed to be abating; and after 12 hours, it was gone. The venom appeared to have only a local neurotoxic effect.

Later, 14 more specimens were found in the same house, apparently having come from the adjacent shrubbery. Subsequently, an active specimen could not be induced to bite a man when placed on an area of thin skin, indicating that this spider is not pugnacious. However, a number of persons have been bitten by it in Hawaii, suffering moderate to grave symptoms (Furman and Reeves, 1957).

Another species, C. mildei C. L. Koch, indigenous to Europe, north Africa, and the Middle East, was considered to be probably responsible for necrotizing skin lesions seen in 5 persons in the vicinity of Boston, Massachusetts (Spielman and Levi, 1970). (Loxosceles reclusa, also responsible for necrotizing lesions, does not occur in the New England states.) Chiracanthium mildei was introduced into the United States, and has spread from New England south to Alabama and west to Utah, also occurring in California (Bryant, 1951; Spielman and Levi, 1970). This species is 7 to 10 mm in body length, and has a pale-brown cephalothorax and white abdomen. It inhabits thickets and hedgerows, but adapts well to life in homes and other occupied buildings. Minton (1972) described symptoms and treatment of a woman bitten by this spider while swimming in a heated indoor pool in Indiana.

Tarantulas (Theraphosidae)

The tarantula is the largest spider in the United States. It is not ordinarily a household spider, and in fact the encroachment of civilization greatly decreases its numbers in an area. Nevertheless, as more and more people build their homes in formerly wild foothill or desert areas, we receive an ever larger number of reports of tarantulas being found in houses.

The tarantula is an interesting spider because of its huge size (up to a 5-in. [13-cm] leg span) and forbidding, hairy appearance, which have given it an undeservedly sinister reputation. Baerg (1922) allowed himself to be bitten twice, and stated that the bites felt like pinpricks, with mild pain lasting only 15 to 30 minutes, not accompanied by inflammation or swelling. Tarantulas are very sluggish, and will not bite unless provoked. They are unlikely to bite even when picked up if they are handled gently. Some people keep them as pets; a good place for this is in a small, empty aquarium with a sandy bottom. A small clay flower pot, laid on its side and with sand at the bottom, may be put at one end as a hiding place. A jar lid can be sunk into the sand nearby to serve as a container for water. Tarantulas should be fed live insects. It is convenient to use live crickets, which can be purchased from some suppliers of fish bait. The female spider can live as long as 20 years in captivity, and even longer in the wild state.

There are some 30 species in the United States, mostly in the southwestern area. The light- to dark-brown Aphonopelma californica (Ausserer) (= Eurypelma = Dugesiella) (plate VI, 8; figure 216) is the principal species, usually found on the dry, southern slopes of hills. It is the largest of the United States spiders, being up to 5 in. (13 cm) in total length. It is covered with velvety wool and long, silken hairs. The male may be black or reddish brown, and is usually much darker and has a smaller abdomen than the brownish female. Another tarantula, Dugesiella hentzi (Girard), more common in Arkansas, Oklahoma, and Texas, has often been called Aphonopelma californica.

Tarantulas either burrow into the ground or utilize small holes of suitable diameter near rocks, roots, or other objects. They line their tunnels with silk, and form a neat, webbed rim at the entrance or conceal it entirely. They generally travel at night, and usually those seen wandering about in the open are adult males. It requires 10 years for tarantulas to reach maturity. The males enter the burrows only in mating season, from July to November. Many are killed by the females, and others die from many hazards, including man. On the other hand, the females may live for 25 years or more, the longest-lived spiders known. The females molt after maturity, but the males do not (Levi et al., 1968)

Other Species of Venomous Spiders

Although all but 2 small groups of spiders are venomous, the fangs of most species are too short or too fragile to penetrate skin. Nevertheless, in the United States at least 50 species have been implicated in bites on humans. Aside from the species already discussed, those which have produced some local or systemic effects include the following:

Pamphobeteus, Phoneutria, and Cupiennus salei are not native to the United States, but are sometimes introduced in produce or other materials (Anonymous, 1970g; Russell, 1969).

Of the 5 species of spiders other than Latrodectus spp. and Loxosceles spp. that Waldron (1965) was able to identify with cases of arachnidism (poisoning caused by the bite of an arachnid) in southern California, only a single species, Neoscona vertebrata, which bit the back of the hand of an adult man, caused an ulceration 1 in. (2.5 cm) in diameter. The others were Phidippus formosus (Peckham) (figure 217), (3 cases), an immature Misumenoides aleatorius, Chiracanthium inclusum, and Araneus sp. The symptoms in these cases included initial pain, redness, and sometimes swelling. Marks caused by the spider's chelicerae were observed in all cases. A woman bitten by Phidippus formosus reported that the bite area on her leg was sore and tender for almost 6 weeks. A 16-year-old boy bitten by Araneus sp. noted no swelling, but the pain lasted about 4 days.

Phidippus formosus bites aggressively and, unlike Latrodectus and Loxosceles, it does not have to be stimulated to bite. While photographing the specimen shown in figure 217, the photographer was bitten twice on the back of his left hand. The swelling gradually increased until in 4 days it involved the entire back of the hand and the fingers. The back of the hand was sensitive to touch and pressure, and itched severely. The swelling and a dull pain lasted for 9 days (Russell, 1970).

Importance of Submitting Captured Arthropod When Bitten

It is important to try to capture the arthropod that does the biting and submit it to the proper authority for identification. The stings and bites of bees, wasps, mosquitoes, biting flies, fleas, bed bugs, lice,.ticks, and mites are far more common than spider bites, and some of these arthropods can produce bulbous lesions that may rupture and ulcerate. Many reports of necrotic or gangrenous arachnidism currently attributed to Loxosceles reclusa, especially in areas where it is not likely to be found, may be traceable to other species of spiders. Bites from some of the spiders just listed, while not causing as severe symptoms as those caused by L. reclusa, can be serious enough to warrant hospitalization and intensive care (Russell et al., 1972).

Although most bites or stings by arthropods are not likely to be dangerous, medical care or advice should be sought in each case. Regardless of the offending animal, rest or decreased activity is always indicated, and reassurance should be given to the victim. According to F. E. Russell (personal communication), of the millions of stings and bites by arthropods each year in the United States, fewer than 10 persons die as a direct effect of the venom. More than 50 deaths per year are attributable to the sensitivity reactions to venom proteins, usually to those of Hymenoptera. Irrespective of the arthropod involved, whenever possible it should be sent with the victim to the physician or medical facility so that proper identification can be made. This is particularly important in the case of a spider or tick bite or a scorpion sting.

Treatment for Spider Bites

There are no first-aid measures of value for bites by the black widow spider. If the pain is severe, an ice cube may be placed on the bitten spot to reduce pain. It should be removed when antivenin is injected. The same measures recommended for scorpion stings - immediate immobilization of the affected part, decreased activity or complete rest, and reassurance - are indicated. Hospitalization is usually advised for all patients under 16 or over 60 years of age, those with hypertensive heart disease, or symptoms and signs of severe envenomation. (Such symptoms and signs for the black widow spider and for the brown recluse are described on preceding pages.) In case of a black widow spider bite, 1. ampule of Latrodectus mactans antivenin should be given as soon as possible at a medical facility following the appropriate skin or eye test. Patients with a history of hypertensive heart disease should receive mild sedation, and appropriate measures for reducing the blood pressure should be instituted, if necessary. For adults, treatment usually consists of the administration of muscle relaxants or calcium gluconate, hot baths, aspirin, and mild sedation. In all cases, the patient should be advised to rest for 12 hours. The symptoms and signs of black widow poisoning rarely persist, even in an untreated patient, for more than 2 days (Russell, 1969).

Treatment for Loxosceles bites is largely empirical. Most authorities agree that in order to be effective, treatment must begin within the first 24 hours following the bite. Local excision of the wound appears to be the method of choice when the case is seen within 12 hours. Thereafter, steroids appear to be the drugs of choice, but even these must be administered early to obtain a good result. Antihistamines are of questionable value (Russell et al., 1969; Asel, 1969; Russell et al., 1972).

Although Loxosceles is the only spider at present implicated in the syndrome known as "necrotic arachnidism," many arachnologists and physicians feel that it is quite possible that other genera might be implicated in this syndrome in the future. A number of new drugs are now being tried for the treatment of the necrotic lesions produced by spiders, and some show promise.

Control of Spiders

The habitats of the black widow and brown recluse spiders in buildings are similar to those of any building-invading spiders - in corners, under and behind furniture and household appliances, in undisturbed clutter in the garage or workshop, piles of lumber, boxes, and debris, and in the crawl spaces under buildings. Premises should be cleared of rubble, scrap, and lumber piles, but care should be taken not to accidentally imprison or crush spiders with the fingers or other body surfaces. The female black widow spider may rush out and bite when her web is disturbed. Most spiders will bite, or attempt to bite, when they are accidentally trapped in clothing or shoes.

Any secluded and seldom-disturbed location may provide harborage for spiders. Webs should be destroyed, or may be sprayed or dusted. Suspect areas may be sprayed or dusted with insecticides such as lindane, chlordane, diazinon, or chlorpyrifos, using concentrations recommended on the package labels. The crawl space can be most effectively treated with an insecticide dust, which can be applied from the crawl hole and foundation vents. Large hand dusters may suffice for dusting extensive areas, but equipment that can apply a dust with greater velocity, such as an electric blower or a modified water-type fire extinguisher, is desirable. The silica aerogel Dri-die 67, available only in 15-lb. (7-kg) bags, is useful for attics, wall voids, and other enclosed or unused places, for it leaves a permanent film of protection against reinvasion by spiders as well as other cryptobiotic arthropods.

Lindane has long been considered to be the most effective insecticide for control of the brown recluse spider (Wingo, 1964; Hite et al., 1966; Norment and Pate, 1968), but more recently resmethrin, closely related to the natural pyrethrins, was found to be just as effective in topical application (Gladney and Dawkins, 1972). On the other hand, dichlorvos was relatively ineffective, even by topical application, and the fumigant action of dichlorvos strips was practically worthless; out of 30 spiders of all ages, the first adult male died after 33 days and no adult female died after 60 days of exposure.

Spiders feed principally on insects, and any measures taken to decrease the number of insects in a building will also decrease the number of spiders. Spraying for spiders also decreases the number of insects in the vicinity upon which the spiders feed. Newly hatched spiders can enter the home through screens or around loose-fitting windows and doors, but the older ones can be kept out by careful screening. Spiders of all stages can be introduced into homes with firewood, plants, boxes, and many other items. Within the home, the white egg cases can be eliminated with a vacuum cleaner. The bag of the vacuum cleaner should then be emptied before the eggs have had a chance to hatch.

Particularly in the warmer parts of the country, where control is necessary, it is advisable to treat for spiders outdoors as well as in the house. A residual-type insecticide should be applied to coves, eaves of porches, low roofs, window wells, around door and window frames, and to a 3- to 5-ft (1- to 1.5-m) area around the foundation, as well as to the foundation itself. It is also desirable to treat the garage, shed, or any other outbuilding on the premises, as well as piles of old lumber, woodpiles, weedy areas, and fences. Check the label on the insecticide package to make sure it will not be injurious to any of the plants and shrubs in the area to be treated. Dusts or liquid sprays of chlordane, diazinon, or propoxur (Baygon) have been effective against spiders outdoors. A dust is easier to apply and will penetrate more effectively into woodpiles, dense weed patches, or inaccessible areas in the garage. The spiders will succumb after they crawl over the residue, either on their webs or in adjacent areas.

As is the case with other pests already mentioned, a treatment may be adversely affected if the toxicant repels the spider from the spray residue. Malathion and propoxur, for example, have been found to be highly repellent to brown recluse spiders, at least for a period of 2 weeks, and sometimes longer (Sterling, 1970). To overcome this effect, an attempt might be made to contact the spider with the spray or to treat a large enough area so that it is forced to pick up a lethal quantity of the toxicant while attempting to escape.


Scorpion Species List

Scorpions are most abundant in warm parts of the world, and particularly in semiarid regions (see chapter 4). In areas that occasionally have subfreezing temperatures, they remain in the warmer crevices of cliffs and piles of rock, and lie dormant during cold periods. Despite their usual occurrence in dry climates, scorpions need access to moisture, for they drink water. Their nocturnal habit and tendency to inhabit shady crevices reduce the evaporation of their body fluids. The crevices may also provide moist microclimates, or they may be extended and connected by the scorpions to moist areas in the soil. In the United States, scorpions are most abundant in the arid Southwest, and they are rare north of a line traced from Baltimore to St. Louis, Salt Lake City, and San Francisco (Scott and Pratt, 1957).

Like spiders and ticks, scorpions can withstand starvation for a long period, 4 or 5 months being common. Scorpions emerge from their hiding places at night and prey upon ground-inhabiting insects and other small animals, including small mice. Even in the dark, the scorpion is aware of approaching prey because it can detect slight air movements and minute vibrations. It blindly grasps its prey with the chelae of its large pedipalps, which are always kept in a forward position, and stings it. Normally, the "tail" of a scorpion is extended horizontally, and the stinger, situated in the bulbous last segment, curves downward. However, when the scorpion readies itself for attack or defense, the entire tail-like postabdomen is curved dorsally and forward, the stinger then curves upward (figure 36, chapter 4), and the victim is stung quickly and repeatedly.

Around the home, scorpions are most commonly found in the crawl space under the house and in the attic, which they usually enter by way of the wall voids. They seek water, and sometimes may be seen in washrooms, kitchens, and bathrooms where water is available, although during the day they are more likely to be seen in closets, shoes, folded blankets, or similar retreats. Ground scorpions (all scorpions other than Centruroides spp.) frequently burrow into children's sand boxes or gravel banks, where they can remain buried without food or water as long as 6 months .(Stahnke, 1966).

Sculptured Scorpion, Centruroides sculpturatus Ewing (Buthidae)

Few species of scorpions are deadly to humans, but they are all venomous, and envenomation by arachnids should always be considered as potentially dangerous. The most venomous species in the United States is the deadly sculptured scorpion, Centruroides sculpturatus (plate VII, 1; figure 218). It is comparatively small and slender, and may be yellowish or straw-colored over the entire body, or may have 2 irregular, blackish stripes lengthwise along the dorsal surface. This striped form is a color phase formerly considered to be a distinct species, C. gertschi Stahnke. In fact, 4 color phases of C. sculpturatus have been recognized by Stahnke (1971). He stated:

Centruroides sculpturatus is to be recognized as a species ranging from a primarily concolorous condition to 3 color phases bearing various interstices of fuscous stripes along the trunk dorsum, on the ventral surfaces of the caudal segments, and some fuscous marbling on the lateral surfaces of the legs. All evidence is unfavorable for recognizing subspecies taxa.

This species ranges from about 12 mm in length when the young first leave the mother's back to about 7 cm when full grown, the males being generally longer and more slender. The adult female's body is not more than 10 mm in width, and the male's is 7 mm at the greatest dimension. The "tail" of the female may be a little over 2 mm in diameter, and that of the male even less. The pincers are very slender - about 6 times as long as the greatest width. At the base of the stinger is a little blunt thorn that is lacking on all other known Arizona scorpions (Stahnke, 1948). Centruroides sculpturatus is principally an Arizona species, ranging only a short distance into New Mexico and Mexico.

The sculptured scorpion caused 75 deaths in Arizona from 1926 to 1965, twice as many as from all other venomous animals, including Arizona's many species and subspecies of rattlesnakes and the Sonoran coral snake. Most of the deaths were those of children under 16 years of age (Stahnke, 1966).

Three Related Forms

In Big Bend National Park, Texas, there is a scorpion, Centruroides pantheriensis Stahnke, that superficially closely resembles C. sculpturatus, but has venom more like that of the Big Bend scorpion, C. chisosarius Gertsch, and the common striped scorpion, C. vittatus (Say), which ranges from South Carolina to Kentucky and west to New Mexico and Mexico (Stahnke, 1956a). Preliminary evidence indicates that these 3 are all the same species (Stahnke, 1971).


Stings by most species of scorpions are not likely to be serious, usually resulting in localized pain and paresthesia, some swelling and tenderness and, on occasion, localized ecchymosis (black-and blue areas) and the formation of vesicles (Stahnke, 1956b; Russell et al., 1968). However, stings by certain Centruroides species common to parts of Arizona and New Mexico may be fatal, as already stated. Stings by Centruroides are often very painful and give rise to immediate distress, including numbness about the wound which may rapidly spread to involve the entire extremity, weakness or even paralysis of the injured part, hyperactivity and anxiety, profuse salivation, dizziness, difficulties in speaking and swallowing, respiratory distress, and in some cases convulsions (Shannon, 1965). The site of the sting does not swell or become discolored as it does with other less dangerous species (Scott, 1966b).

Centruroides sculpturatus venom administered to anesthetized dogs and cats caused hypertension, respiratory failure, and skeletal muscle stimulation. The animals developed an intermittent gasping form of respiration which progressively diminished in amplitude and frequency until death resulted from anoxia (deficiency of oxygen reaching tissues of the body) (Patterson, 1960).

Preventive Behavior to Avoid Bites and Stings

According to Stahnke (1966), 2 principles of action would make an individual almost free from the danger of envenomation:

  1. Never thrust your hand or kick your foot where the eye cannot see.
  2. If you feel something crawling on your body during the night, or on the back of your neck, etc., don't swat, brush! If it is a stinging or biting arthropod, the swatting action will guarantee envenomation, but a quick brush will catch the invader by surprise and remove it before damage to the host can occur.

The first principle applies to vertebrate as well as invertebrate venomers.

Treatment if Bitten or Stung

The first thing to do is to summon a physician and keep the patient warm. Stahnke (1965, 1966) emphasized the importance of protecting the bitten or stung patient as much as possible from emotional concern and stress, stating that stress might more than double the toxicity of rattlesnake or scorpion venoms, and that the increased toxicity appeared to be caused in part by the synergistic action between the venom and epinephrine which was discharged into the bloodstream under conditions of emotional stress.

In scorpion stings, if available, an ice cube can be placed over the wound and the part immobilized. The ice can be left in place until the patient is seen by a physician. The cooling reduces pain, but prolonged exposure to the ice should be avoided. Incision and suction are not indicated, and the use of a tourniquet should be avoided except when the symptoms indicate anaphylactic shock. In the event that ice is not available, the area should merely be cleansed, the injured part immobilized, and the patient taken as quickly as possible to the nearest medical facility. Exertion should always be kept at a minimum. If there is a long delay in transit, respiratory distress may develop, and it may be necessary to give artificial respiration. Protective measures may also be required in case of convulsions. Antivenin is available for Centruroides stings, and can be obtained by a physician or hospital when needed. The location of the nearest source of antivenin can be obtained from the district Poison Control Center. Under no circumstances should a lay person administer antivenin in the field. Supportive meastires for stings by Centruroides include vasopressor agents, atropine, oxygen, and pentobarbital in cases where convulsions occur (Russell, 1969).

The "ligature and cryotherapy" (L-C) technique in the treatment of snake bite or scorpion sting has long been advocated by some authorities, and therefore some mention of it should be made at tliis point. This is the treatment that involves placing the bitten member in iced water to a point well above the wound. The treatment is considered to be dangerous by most physicians. Many people on whom this treatment has been practiced have had to have the affected arm or leg amputated.

Control of Scorpions

As in the control of spiders, the elimination of harborage places, such as piles of wood and trash, is important. Lumber and firewood should be stored off the ground. Spraying or dusting of the areas surrounding the house with insecticides of long residual action is useful for killing scorpions and also for reducing the supply of insects upon which they feed. Scorpions in a house are found most commonly under the building (crawl space) and in the attic. However, they shun temperatures above 100 °F (38 °C), and when the attic gets too hot, they will move downward into the living space where they are attracted to the kitchen, bathroom, and other rooms where water is available.

Insecticide dusts, such as 50% chlordane, are preferred for treatment in the house because they can be blown into wall voids and attics. A longlasting insecticide is desirable, for scorpions may remain in such places for a long time. Sprays of chlordane or diazinon are also effective when applied to baseboards, under furniture, and other hiding places (Stahnke, 1948; Homer, 1969).

CENTIPEDES (Chilopoda)

Centipede Species List

Centipedes are long, flattened, many-segmented arthropods. Most of the segments have a pair of legs (plate VII, 2). They may be found in damp locations under leaves, rotten logs, stones, or boards, and run swiftly when disturbed. They prey on many species of arthropods, earthworms, snails, and other small animals, killing them with their maxillipeds or toxicognaths, appendages on the first segment behind the head. These have strong, piercing, terminal segments with orifices of ducts that lead to venom glands (figure 219). [Spiders are the only arthropods in which the venom glands open through the chelicerae (figure 207).] Centipedes are long-lived, some species living as long as 5 or 6 years. Many species of centipedes can inflict venomous wounds on man, but these rarely result in death. Wounds caused by a centipede's claws (maxillipeds) should be disinfected and a physician should be consulted (Scott, 1966b).

House Centipede, Scutigera coleoptrata (L.)

The house centipede came from Mexico, but is now distributed throughout the United States. It often invades houses, particularly if subfloor areas or basements are damp. It searches for insects at night. Unlike other centipedes in the United States, it is able to reproduce within the house. It occurs both indoors and outdoors in the warmer regions of the country, but only indoors in the colder regions. It runs rapidly, holding its body well elevated by means of its conspicuously long legs, then suddenly stops, remains motionless, and with equal agility runs again to a place of concealment (Back, 1939). There are only a few records of this species wounding man, resulting in pain no more severe than that of a bee sting (Curran, 1946b).

Description. The house centipede (plate VII, 2; figure 220) has a very strange appearance. It is 2.5 to 4 cm long, with very long, slender antennae, and with 15 pairs of legs, also very long. In the female, the last pair of legs is more than twice the length of the body. The grayish-yellow body has 3 longitudinal dorsal stripes, and the legs are banded with white (Back, 1939). This species is in an order (Scutigeromorpha) in which all species have 15 pairs of long legs and long antennae, and are the only centipedes with compound eyes, the others having clusters of ocelli. They can readily detach their legs if they are grasped by an enemy.

Life Cycle. When the larvae hatch from the egg, they have 4 pairs of legs. There are then 5 more larval stages, with 5, 7, 9, 11, and 13 pairs of legs, respectively. Thereafter, there are 4 adolescent stages, each witli 15 pairs of legs (Cloudsley-Thompson, 1968).

Other Western Species

In the West, the large Scolopendra polymorpha Wood (plate VII, 2) can attain a length of 15 cm, and its venom-bearing claws can cause severe pain and swelling. Its claws can scratch the skin, and such scratches should be disinfected to prevent secondary infection. The large, greenish Scolopendra heros Girard, which occurs in southern California, can not only cause severe pain and swelling by its venom, but can produce a reddish streak where it has crawled upon the body. Its numerous feet make many incisions into which it drops venom that causes intense irritation and leaves 2 rows of white punctures (CloudsleyThompson, 1968).

Control of Centipedes

For control of centipedes outdoors, the removal of damp harborage places, such as piles of trash, rocks, boards, leaves, grass, and compost, is desirable. In addition, it may be necessary to spray or dust with such insecticides as chlordane, dieldrin, or carbaryl at the concentrations used for most insects (as stated on the package labels) on and around foundations and into the subfloor crawl space of the house.

For control of the house centipede, Scutigera coleoptrata, sprays of 20% malathion, 0.5% diazinon, or 0.5% lindane have been found to be effective when applied to baseboard crevices, cracks, openings in concrete slabs, or other hiding places. Dusts of the same insecticides are useful to blow into wall voids and crawl spaces.


Ants Species List

The common household ants have been discussed in some detail in chapter 6. At this point, only certain species will be discussed that do not commonly invade the home, but occur outdoors and inflict especially painful bites or stings. They are pests principally in the yard and lawn and in recreational areas. The best-developed stingers and a potent venom are possessed by species in the subfamily Ponerinae, considered to be the most primitive ants. However, many species of ants in other subfamilies sting. Other species do not possess a stinger and merely bite, but some of these inject a venom into the wound, causing considerable pain (Snelling, 1970).

In the more primitive subfamilies of ants, the venoms are proteinaceous, corresponding to those of wasps and bees. In the fire ant (Solenopsis), the venom is an alkaloid, noted at the end of this section. In the highly evolved subfamily Formicinae, containing such genera as Formica, Prenolepis, Lasius, and Camponotus, the venom glands secrete large quantities of formic acid, believed to be a remarkable chemical simplification in the evolutionary pattern (Cavil and Robertson, 1965). The formic acid reaches intradermal or subdermal tissues only through wounds made by the mandibles. The tip of the abdomen is twisted forward, and the formic acid is sprayed into the wound from glands in the anal region. Envenomation from ant, wasp, or bee stings is discussed under "Hymenopterism" in this chapter, preceding the section on venomous snakes.



southern fire ant, Solenopsis xyloni McCook

Fire ants get their name from the severe reaction caused by their stings. The southern fire ant ranges from California to southern South Carolina and the northwest corner of Florida. In California, it occurs at lower altitudes from southern California up through the Sacramento Valley, but seldom or never along the coast in the northern or central sections. In the literature, the California form is usually designated as a subspecies (S. x. maniosa Wheeler), but ant taxonomists now believe that this is a synonym.

This species is probably our most common native ant, but like some other ants, both its actual and. relative importance are declining, particularly in urban areas, as the Argentine ant increases in numbers and range of distribution. However, wherever the Argentine ant is successfully controlled, the fire ant make a rapid resurgence. The workers are ordinarily slow-moving when compared with Argentine ants. However, they are sensitive to vibrations or jarring. If their nest is stepped on, the workers rush out and sting the feet and legs of. the intruder. There is a great variation in the way people react to ant stings, depending on their degrees of allergy, but an infant was reported to have been stung to death by southern fire ants (Smith, 1965).

Description. The worker (figure 221, A, and figure 222, top) is 1.6 to 5.8 mm long, with yellowish red head and thorax and black abdomen. There are 2 nodes in the petiole and 2 segments in the antennal club. The body, especially the abdomen, is usually very hairy. The workers are polymorphic; the great difference in size is the result of there being 2 forms: the worker minor which is generally the form that stings, and the worker major, which rarely stings. Both forms bite. The females average about 6.6 mm long, and are light reddish brown except for the abdomen, which is black. The males are reddish black, with reddish yellow legs. Winged forms are often observed in large numbers in store windows (Eckert and Mallis, 1941; Smith, 1965).

Biology. The southern fire ant is largely a ground-nesting species, with nests either exposed or under cover of stones, boards, and other objects. When exposed, the excavated earth is usually placed in irregular, cratershaped masses of loose soil. Mounds in lawns cause much damage. Fertilized females have often been seen establishing nests alone. However, more than 1 female is involved in founding a new colony; there may be as many as 12 or more reproductive females (R. R. Snelling, personal communication). The biology has not been completely studied.

Habits. Besides nesting in earth, S. xyloni also nests in wood, sometimes in the wood or masonry of houses. Nests also occur in cracks in soil or in sidewalks. When the ants are outside in the vicinity of the house, they are usually near the kitchen. They travel in trails, and are relatively slowmoving when compared with most other ants. Sometimes the nests are in wall voids, and the ants may then emerge from crevices and between sink tiles (Mallis, 1938).

According to Smith (1965), the southern fire ant is practically omnivorous, feeding on seeds, honeydew, flesh, the juices or sap of fruits and plants, and household foods such as nuts, cereals, cookies, butter, grease, meats, and fruits. It takes seeds from seedbeds, kills young or newly hatched poultry and wild birds, girdles nursery stock such as citrus and pecans, destroys fruits and vegetables, tends honeydew-excreting insects, removes the rubber insulation from telephone wires or electrical wires of traffic signals, and gnaws clothes, silks, woolens, linens, and cotton articles. A pest control operator reported finding fire ants in a nylon viscose rug, where they had caused damage similar to that of carpet beetles. The rug had probably been contaminated with some food substance. The southern fire ant is aggressively predaceous on live insects, but will eat dead ones.

fire ant, Solenopsis geminata (F.)

This species (figure 221 , B) ranges from Texas to South Carolina and Florida and south Brazil and Peru. It does not occur in California. resembles the southern fire ant, except that its head is much larger and the petiolar node is higher, narrower and, in profile, bladelike at the summit. It also closely resembles that species in biology and economic importance (Smith, 1965).

red imported fire ant, Solenopsis invicta Buren

This fire ant (figure 221, C), apparently indigenous to central Brazil (Buren, 1972), is now a serious pest throughout much of the southeastern United States, and occurs as far west as Texas. It infests almost any type of land except swampy areas and dense forests, constructing large, hard, earthen mounds that interfere with cultivating and harvesting operations and cause damage to farm machinery. The ants are very pugnacious, and painfully sting people and farm animals. More than a million persons are estimated to be stung each year by fire ants in the southeastern states. They sometimes nest in houses. Without continued control measures, the red imported fire ant could spread westward to the Pacific and as far north as Oregon and, in the East, to as far north as New jersey (Anonymous, 1973b).

The literature before 1972 refers to the imported fire ant as Solenopsis saevissima richteri Forel, which was believed to comprise a red and a black form. The black form was known to have been in the Mobile, Alabama, area since 1918, and was probably introduced from Argentina or Uruguay. The red form, probably introduced from the Matto Grosso of Brazil, was also first noted in the Mobile area, but not until the early 1940's. It is more vigorous than the black form and has largely replaced it, marking the beginning of the explosive increase in the imported fire ant population in the United States. The black form is now found only in a small area of northern Mississippi. Buren (1972) considered the black form to be a distinct species, Solenopsis richteri Forel, and the red form to be a new species which he named S. invicta. These 2 species are currently being referred to in the literature as the black imported fire ant and the red imported fire ant, respectively (e.g., Banks et al., 1973). The voluminous literature on the biology and control of "S. saevissima richteri," earlier than 1972, refers almost exclusively to what is now known as S. invicta.

Description. The red imported fire ant (figure 221, C) closely resembles the southern fire ant (figure 221, A), but can be distinguished from it by the 4 teeth along the biting edge of the mandible, as shown in the figure; the southern fire ant has only 3 such teeth.

Biology of the Imported Fire Ant. Based on observations made along the Gulf coast in Mississippi, alates are most abundant in early spring, and may comprise as much as 9% of the colony in June. Then, a decreasing number of alates is produced, until production of this caste ceases completely in September. During the 8-month developmental period (April-November), an average colony may produce an estimated 1,500 females and 2,500 males (Markin and Dillier, 1971). Mating flights of male and female ants will occur from large mounds during warm days of most months of the year (Green, 1962). The production of workers begins in March, and peaks of production occur in May and October. Colonies producing mounds between 25 and 65 cm in diameter might contain between 30,000 and 100,000 workers, and over the period of a year they were found to average 76.3% of the colony (Markin and Dillier, 1971).

As many as 1,000 colonies of the imported fire ant have been observed per acre (0.405 ha) under ideal conditions. However, 20 to 30 mounds per acre is the more common number, and the mounds gradually increase to about 45 to 90 cm (18 to 36 in.) in diameter. Sometimes, "giant mounds" 30 to 90 cm (1 to 3 ft) high and 150 to 240 cm (5 to 8 ft) in diameter are formed, possibly as the result of a number of colonies moving together under adverse soil conditions. Adjoining areas are uninfested. The giant colonies may disperse again to form the characteristically smaller ones (Green, 1962).

There is normally little or no movement or communication between adjacent colonies, and discrete territorial boundaries are observed by the ants. As a result, if ants in a colony have access to mirex bait, for example, they will all be dead in 1 to 3 weeks, whereas those in neighboring nests will still be very active (Wilson et al., 1971).

Habits. Imported fire ants gnaw into the roots, stems, buds, and fruit of plants, sucli as cabbages, collards, okra, eggplant, and field peas, or seriously injure young trees by girdling or removing the outer bark from roots or trunks. Citrus nursery stock is especially subject to attack (Smith, 1965). The ants are often so numerous that the gathering of vegetables and other crops is almost impossible. They are also a menace to wild animals and to the eggs and young offspring of ground-nesting birds. However, imported fire ants are principally predators against other insects (Wilson and Oliver, 1969).

Envenomation. The structures of the stinger and poison sac of the imported fire ant were studied and illustrated by Caro et al. (1957). Also, the histopathology of biopsy specimens of volunteers who allowed themselves to be stung was investigated. The ant first pinches up the skin with its mandibles, raising it slightly, and this in itself causes pain. The ant then arches its back at the petiole and inserts its stinger, usually maintaining this position for 20 to 25 seconds. Then, using its head as a pivot, it may rotate and insert its stinger in 2 or 3 additional places, causing a clustering of sting sites that is useful in diagnosis. Sometimes 2 minute, bright-red, hemorrhagic punctures may be seen at the point where the mandibles entered. Within several minutes, a wheal 4 to 8 mm in diameter appears, and by. that time the stinging sensation lias subsided. Within 24 hours, a pustule 2 to 3 mm in diameter appears (figure 223, top). In 3 to 8 days, the purulent material is absorbed or sloughed off, and leaves a smooth, pink area 2 to 3 mm in diameter. This persists for several weeks, and then scar tissue gradually develops (figure 223, bottom). The pustular lesions are often arranged in a circular pattern. Thousands of the lesions were found on inebriated persons who inadvertently disturbed an imported fire ant mound (Smith and Smith 1971).

Whereas the venoms of stinging ants are typically proteinaceous, the venom of the imported fire ant was found to contain an alkaloid, trans-2-methyl-6-n-undecylpiperidine (solenopsin A) or its mirror image, and the structural formula for the compound was determined. This is apparently the first record of an alkylated piperidine being described from a venom of animal origin. The venom is soluble in organic solvents but insoluble in water. It is a potent necrotoxin, and also has pronounced hemolytic, phytotoxic, insecticidal, and antibiotic activities (MacConnell et al., 1970). Five unique alkaloids were finally identified (MacConnell et al., 1971).

Harvester Ants

Harvester ants, so called because they gather seeds and grasses, are large red to dark-brown ants, usually 5 to 6 mm or more in length. All but 1 of the 22 species of the United States occur west of the Mississippi River. Most species have 4 fringes of long hairs on the posterior surface of the head, and these comprise the psammophore. With the psammophore they clean their legs and antennae, carry water, and remove sand during the excavation of their nests. They can carry 4 times more very fine sand than they could with the mandibles alone. Some species are also characterized by many small, parallel ridges on the head.

Harvester ants do not invade the home, but their nests may be found in areas surrounding the house. When houses are built in areas infested by them, these insects can constitute a severe problem. They build their nests, with big craters, in lawns and yards. The nests of California species consist of 1 or more holes with a surrounding low, flat crater about 6 in. (15 cm) across and surrounded by large, vegetation-free areas. Some ants bring seeds into the nest, often with husks and air floats attached. The air floats and refuse are then taken out of the nest by other ants, which deposit the material on the outer edge of the crater. If the nest is disturbed these ants bite the intruder and hang on tenaciously while inflicting a very painful sting.

Harvester ants are considered to be the most aggressive and pugnacious ants in the United States. The reaction to their stings is not localized, but spreads along the lymph channels. Long after the original pain of the sting has ceased, intense discomfort may be felt in the lymph glands of the axil or groin (Creighton, 1950).

California harvester ant, Pogonomyrmex californicus (Buckley)

This species (plate II, 6: figure 222, center; figure 222, top) is 5.5 to 6 mm long, light rusty red with somewhat lighter legs, and the thorax lacks spines. In southern California, the nests are closed continuously during the winter, and every night for the remainder of the year. At 70 °F (21 °C), the ants are sluggish, and maximum foraging activity occurs when the temperature at the ground's surface is 90 to 115 °F (32 to 46°C). Swarming occurs during certain clear, hot days in June and July (Michener, 1942).

Wheeler and Wheeler (1973) state that P. californicus, in well-established colonies, "is undoubtedly the fiercest, the boldest, and the most irascible ant of the Sonoran desert," the quickest to sting, and the effects of the sting are the most painful. Like the sting of the honey bee, but unlike the sting of most ants, its stinger easily becomes detached and remains in the wound. The Wheelers give a number of personal case histories of severe reactions to the sting of P. californicus, describing symptoms that persisted in one form or another for as long as 37 days.

rough harvester ant Pogonomyrmex rugosus Emery

This harvester ant (figure 224, bottom) is 4.9 to 7.2 mm long, and varies from brownish black to various combinations of brownish, yellowish, and brownish black. The petiole always has a few hairs underneath. This species occurs from California to western Texas, in the chaparral belts and the upper desert mountains. It is very aggressive, and inflicts a painful sting (R. R. Snelling, correspondence).

western harvester ant, Pogonomyrmex occidentalis (Cresson)

This is a red ant, 10 mm long, that builds large mounds 4 to 12 in. (10 to 30 cm) high and 24 to 36 in. (60 to 90 cm) in diameter. The galleries honeycomb the soil beneath to a depth as great as 9 ft (about 3 m), and most of them reach a depth of over 6 ft (2 m). There are chambers (granaries) for storing seeds, and others for storing "trash." A chamber containing the queen may range from 10 to 70 in. (25 to 180 cm) in depth. Many workers (250 to 1,200) share the queen's chamber. The number of workers found in 33 excavated colonies ranged from 412 to 8,796 (Lavigne, 1969).

This species occurs at 6,000 ft (1,800 m) or more elevation in Kansas, Colorado, Wyoming, Idaho, New Mexico, Arizona, and Nevada. It is uncommon in California. In one survey in Wyoming, the cleared area around the mounds averaged 88 sq ft (8.2 sq m). Thousands of acres of rangeland had been denuded. The ants had also caused failure of experimental range seedings in one area by gathering seeds or by cutting off young grass plants as they emerged (Lavigne, 1966).

Field Ants

These are medium-sized ants that occur throughout the United States and are quite common. They may be brown, black, red, or various combinations of these colors. The females may be winged or wingless, and usually have a long gaster. The petiole has 1 node. The workers are attracted to insects and honeydew, and are fierce predators of other insects. Many species build nests consisting of large mounds of leaves and sticks around rocks or small trees and shrubs. These ants can be troublesome pests in mountain recreational areas. They bite, and then curve their abdomens forward to inject a secretion into the wound; their bites are therefore very painful.

California red-and-black field ant, Formica occidua Wheeler

These ants (figure 225, A) are 4 to 7.5 mm long have a red thorax, silvery-black abdomen, and the top of the head is dusky brown. They have a characteristic, jerky method of running and stopping. Nests may be found in nature beneath rocks in open, unshaded areas. In urban areas, the nests are often located in cracks in sidewalks, along the sides of buildings, and at the bases of trees. The ants may forage in houses and seek honeydew on trees and shrubs. They have been observed carrying great numbers of workers and sexual forms.of subterranean termites toward their nests (Mallis,. 1941a).

western thatching ant, Formica obscuripes Forel

These ants are 3.8 to 8 mm long, and have a red head and thorax and brownish-black abdomen. They occur from British Columbia to California, at elevations of 5,000 to 8,000 ft (1,500 to 2,400 m). They construct mounds from small sticks, leaves, and pine needles, and often are injurious to seedling trees and native plants near the mounds. They can become pests in mountain cabins.

Formica haemorrhoidalis Emery

This species (figure 225, B) is similar to F. obscuripes in appearance, except tliat pubescence is almost totally absent from its head and thorax. It also has a similar distribution range and habits, except that it is more completely confined to forested areas.

Formica pilicornis Emery

These field ants (figure 222, bottom, and figure 225, C) are 3 to 7 mm long, and have a blackish head and gaster and usually a reddish thorax. They have many erect hairs on the legs, scapes, and eyes, and the abdomen appears grayish because of dense, appressed hairs. They may be found along the coast and throughout the chaparral belt of southern California, nesting in the soil, often under cover, and are frequently very abundant. They often nest in cracks in sidewalks and along sides of buildings. They travel in long trails, and sometimes invade the home. They are diurnal scavengers, and tend aphids and mealybugs (R.R. Snelling, correspondence).

silky ant, Formica fusca L.

Formica fusca (figure 225, D) occurs over much of the United States, but only in the mountains in southern areas (in southern California, above 4,500 ft (1,450 m). These ants are 4 to 6.5 mm long, uniformly blackish, often with bronze tints on the head, and the legs are sometimes reddish. The body is almost devoid of erect hairs such as may be found in F. pilicornis, but the silky pubescence (fine hairs) of the abdomen give this species its common name. The clypeus has a sharp median carina. They nest in the soil, throwing up messy tumuli. They are diurnal, tend aphids, and are general scavenger-predators. They may be attracted to meats, but are much more timid than is the case with F. pilicornis.

Allegheny mound ant, Formica exsectoides Forel

This common eastern species ranges from Nova Scotia to Georgia and from the Atlantic Coast as far west as Ontario, Wisconsin, and Iowa. The head and thorax are rusty red and the legs and abdomen are blackish brown. The workers vary greatly in size, from 3.2 to 6.3 mm, the largest being about the size of the soldiers. The Allegheny mound ant builds the largest anthills of any of the North American moundbuilders. They are rounded cones, 12 to 36 in. (30 to 90 cm) high and often up to 2 cm in diameter. A mound 19 in. (50 cm) high was found to contain 237,103 workers and 1,407 queens. One 10-acre area (about 4 ha) averaging 7 mounds per acre was estimated to contain about 12 million ants. Inside the mounds are many approximately cylindrical passageways about 12 mm in diameter. Passageways also extend down into the ground beneath the mound for a depth of 30 to 36 in. (75 to 90 cm). The ants spread in the spring by swarming and starting new mounds, a moderate distance up to 30 m from the old mounds (Haviland, 1947).

This species girdles small trees and shrubs by injecting formic acid into wounds it makes in the bark with its jaws. It is not a household pest, but can be one in recreational areas (Mallis, 1969).

Control of Ants

Although chlordane is generally used by the homeowner for ant control, good results can be obtained with other common and garden sprays or dusts at the usually recommended concentrations. In field applications, heptachlor and Nonachlor (related to chlordane) at dosages as low as 0.25 lb (0.113 kg) per acre of actual toxicant gave good control of the red imported fire ant (Banks et al., 1966). Mirex and Kepone baits have been suggested where large acreages are treated because less weight of material needs to be transported compared with water- or oil-based insecticides (Lavigne, 1966). In connection with baiting, an interesting observation was made by Haviland (1947) with regard to Formica exsectoides. After feeding on a sodium arsenite-sugar solution bait for several hours, during which several hundred ants died, the remainder stopped feeding, even though no other source of food was available. For 2 weeks they ignored any food placed on the spot where the poison had been placed. It was 6 weeks before they would again feed on a sugar solution, and they never again fed on a poisoned solution. A similar observation was made on red imported fire ants, Solenopsis invicta, by Rhoades and Davis (1967). These ants ceased feeding on a bait when they became aware that it contained a poison, and they moved the colony to another location.

A recent innovation in baits consists of the encapsulation of microdroplets of vegetable oil containing 2% mirex within thin gelatin or plastic coats. These microencapsulated oil baits have been found to be very attractive to the imported fire ant, and give excellent control. The bait can withstand weathering, making it superior to baits used in the past in which mirex has been contained in corncob grits. Lacking a bulky carrier, this type of bait is particularly suitable for application by aircraft (Markin and Hill, 1971).

The first full-scale attempts to totally eliminate the red and the black imported fire ants (S. invicta and S. richteri, respectively) from large areas by aircraft application of mirex bait, using 3 applications at 1.25 to 2.5 lb/acre, indicated that total elimination of the ants from large, isolated areas might be technically possible. The bait consisted of 85% corncob grits, 14.7% soybean oil, and 0.3% mirex (Banks et al., 1973).

J.N. Roney (correspondence) states that, in the control of agricultural ants in Arizona, if insecticide dusts or liquids are applied in the opening of the hill, the ants will make an opening in some other part of the hill. A narrow band of dust around the hill and about 24 in. (60 cm) from the opening is effective. However, dust may cake over after 5 days or so, or if it gets wet and subsequently dries, and the ants can then crawl over the deposit. For this reason, granular formulations of the same insecticide are more effective. A very large anthill may require 2 applications at r intervals of'6 to 8 weeks for control. Liquid formulations must be used in large quantities, and even then results are usually poor. R. R. Snelling (personal communication) has injected calcium cyanide into the soil around the mounds of fire ants and harvester ants with great success.

Figure Captions

Figure 207. External anatomy of a spider. A, dorsal view; B, frontal view of face and chelicerae; C, ventral view, most legs omitted. (From Gertsch, 1949.)

Figure 208. Western black widow spider, Latrodectus hesperus. A, female in normal position, hanging in web; B, mating position, with female represented in outline and male blackened; C, venom glands as seen from above in relation to entire cephalothorax; D, left venom gland, with its duct and left chelicera. (from Kaston, 1970.)

Figure 209. Jaws of most common spiders, suborder Labidognatha (left) and jaws of mygalomorphs, suborder Orthognatha (right). (From Levi et al., 1968.)

Figure 210. Black widow spider, Latrodectus mactans with egg sac.

Figure 211. Western black widow spider, Latrodectus hesperus. A, sixth-instar female, dorsal aspect of a dark specimen; B, the same specimen, ventral aspect; C, sixth-instar female, dorsal aspect of a light specimen; D, fifth-instar female, dorsal aspect; E, fourth (next to last) instar of male, dorsal aspect; F, the same, ventral aspect. (From Kaston, 1970.)

Figure 212. A theridiid spider, Steatoda grossa, a natural enemy of cockroaches as well as of the black widow spider.

Figure 213. Brown recluse spider, Loxosceles reclusa (female). (U. S. Army photo, from Glick, 1969.)

Figure 214. Healing sequence of a lesion on the upper joint of an index finger caused by the bite of a brown recluse spider. The sequence covered a period of 62 days. A, 2 days after bite; B, 4 days; C, 9 days; D, 27 days; E, 38 days; F, 62 days. (Courtesy Mrs. Lena Glick, R.N.)

Figure 215. A brown or violin spider, Loxosceles arizonica, of the southwestern United States. (From Russell et al., 1969, courtesy F. E. Russell, M.D.)

Figure 216. A tarantula, Aphonopelma californica.

Figure 217. A jumping spider, Phidippus formosus. (From Russell, 1970.)

Figure 218. The sculptured scorpion, Centruroides sculpturatus, a very venomous Arizona species.

Figure 219. Venom glands and their ducts on centipede claws. (From Cloudsley-Thompson, 1968.)

Figure 220. House centipede, Scutigera coleoptrata. (From Back, 1939.)

Figure 221. Fire ants. A, Solenopsis xyloni; B, Solenopsis geminata; C, Solenopsis invicta. (From Smith, 1965.)

Figure 222. Some ants with painful stings or bites. Top, southern fire ant, Solenopsis xyloni; center, California harvester ant, Pogonomyrmex californicus, bottom, a field ant, Formica pilicornis.

Figure 223. Results of stings by imported fire ants. Top, pustules 2 to 3 mm in diameter that appear within 24 hours; bottom, pink areas and scar tissue that appear after the purulent material in the absorbed or sloughed off. (Courtesy USDA, Entomology Research Service.)

Figure 224. Harvester ants. Top Pogonomyrmex californicus; bottom, Pogonomyrmex rugosus. (Courtesy R. R. Snelling.)

Figure 225. Field ants. A, Formica occidua; B, Formica haemorrhoidalis; C, Formica pilicornis; D, Formica fusca. (Courtesy R. R. Snelling.)


1996; 2002© Entomology UC Riverside


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