Buildings with sliding glass doors, particularly on slab-on-ground foundations, sometimes allow the entry of certain pests from moist, shady, or secluded places, such as sowbugs, pillbugs, springtails, millipedes, centipedes, earwigs, or oriental cockroaches. Enclosed patios, often with considerable decorative vegetation, have resulted in the introduction of plant pests and soil or humus inhabiting pests into the home. The soil adjacent to the foundation is often shaded, damp, and contains abundant humus and fertilizer. Greater emphasis on the beautification of the yard and garden often involves extensive cultivation of trees, shrubs, flowers, and lawns. Wooden and brick planters are becoming increasingly popular. The insect and other fauna associated with such areas may enter the house directly around doors and windows or via subfloor areas which are protected from the sun and are often cool and damp.
Some pests, such as cockroaches and earwigs, that are favored by both moisture and seclusion, and others, such as silverfish, carpet beetles, cluster flies, face flies, and some species of ants, that are favored primarily by seclusion, have been treated in other chapters of this book under what appear to be more appropriate headings. The insects and other arthropods considered in the present chapter are those that are attracted to any damp area, usually feeding on fungi, and are found in such enclosed places as wall voids only when those spaces become excessively damp for long periods. Among them are fungus beetles, fungus gnats, fungus moths, psocids, springtails, and certain mites. These arthropods all have a protective film of lipid covering their entire cuticles and protecting them from a lethal rate of water loss, even in dry environments. With the exception of the springtails, they are not compelled to live in damp areas, but seek them because they find food there, such as leaf mold or fungal mycelia. (See under "Springtails" in this chapter.) There are other arthropods, such as sowbugs, pillbugs, amphipods, millipedes, and centipedes, that must live in damp areas because they lack the protective lipid film possessed by insects and mites. These are not the pests that deliberately infest damp locations in the home, but must live in the even damper conditions found in many areas surrounding or beneath the house, such as under piles of leaves, grass, peat moss, wood chips, in damp leaf mold, or in cracks in damp earth. They enter homes only as accidental intruders, and cannot.survive there.
In warm, humid regions, such as the Gulf Coast of the United States, air-conditioning is the cause of most condensation problems. Although it might appear, that warm-weather condensation should be prevented by placing a moisture barrier on the warm side (outside) of an insulated wall, research has shown that a moisture barrier installed under wooden siding may lead to serious accumulations of moisture within the siding. Progress in the prevention of condensation in insulated walls in warm, humid regions will depend on further research, but it is already evident that such walls will be relatively free of condensation moisture if they are reasonably permeable to water vapor. Serious condensation of moisture can occur in wooden floors in air-conditioned homes in warm, humid areas if inside temperatures are not maintained below 75 °F (24 °C). Such condensation problems can be prevented by decreasing the humidity of crawl spaces through proper ventilation, soil drainage, soil covers, or mechanical dehumidification (Amburgey, 1972).
A major cause of condensation has been the increase in the daily use of water by occupants of buildings. Each day, a typical family of 4 converts about 25 lb (11 kg) or approximately 3 gal (11 L) of water into water vapor in the air of an average house (Anderson, 1972). High water tables, garden irrigation, etc., can introduce as much as 100 lb (45 kg) of water per day per 1,000 sq ft (93 sq m) into building subareas. If this water is not removed by proper ventilation, it is conducive to infestation by insects and other pests as well as infection by decay fungi (NPCA, 1955).
Rooms are smaller and more airtight than they were a few decades ago, resulting in less air to absorb and disperse the moisture released in household operations. Relative humidity is generally higher than it was in houses built many years ago. The latter generally had large rooms with high ceilings, windows that were not weather-stripped, and their construction details allowed greater air loss and air infiltration. Through central heating, all rooms within a house are likely to be warm, resulting in largescale condensation on and in the cold walls. Water condensing on windowpanes runs down into the sash, sills, framing, and often onto the walls. More houses are being built on concrete slabs, for which there is no subfloor ventilation, and even for conventional construction, ventilation is often inadequate in subfloor areas and attics, which also helps to retain the moisture within the house. With joist-type construction, an effort should be made to ensure adequate ventilation of the crawl space, and a vapor barrier over the soil may be desirable. The moisture problem can also be minimized by keeping windows closed during the day, using a dehumidifier, and raising the inside temperature (Anderson, 1972).
Excessive moisture can result from humid weather, leaky roofs, wet basements, manufacturing and processing operations, evaporative air coolers, and inside venting of plumbing or of machines such as automatic clothes driers (they should be vented to the outside). Clothes driers should be particularly emphasized in this connection because the vent of the machine not only blows hot, humid air into the building, but also contributes a large amount of organic lint that coats the walls and furniture, and upon which mildews can flourish. Insects such as fungus beetles, psocids, and springtails can subsist on the mildew spores (Scott, 1966c).
The construction of concrete or masonry floors, walls, and fireplaces requires large volumes of water. In the construction of a small home with a basement, the concrete floor would have more than 2,000 lb (908 kg) of water when it is poured, the concrete basement walls would have over 4,000 lb (1,816 kg) and, if the house is plastered, over 2,500 lb (1,135 kg) of water would be used for that purpose. The rough frame of a house may be damp when constructed, and rain may add more water before the roof and sidewalls are completed. Because of rapid completion of the building, this water may remain in the house or apartment structure for months after occupancy.
Green lumber is occasionally used in construction, and the building is then quickly enclosed, giving the lumber little chance to dry. This results in "sweating" and high humidities in wall voids, favoring the growth of molds upon which insects can feed. Pests such as fungus beetles and psocids are often problems associated with new construction. When the building is occupied, the artificial heating required for human comfort eventually dries out the lumber, and infestation by mold-feeding insects then seldom reoccurs (NPCA, 1955; Anderson, 1972).
Description. Fungus beetles are very small insects, ranging from 1 to 3 mm in length. They are various shades of brown, varying from light yellowish brown to nearly black. Morphological features of the 2 families are illustrated by the lathridiids Cartodere constricta (Gyllenhal) and Aridius nodifer (Westwood), and the cryptophagid Cryptophagus laticollis Lucas (figure 332). Lathridiids usually have rough surfaces, and the elytra are conspicuously marked by rows of pits and are broader than the exposed parts of the thorax and head. The bodies of cryptophagids are always more or less convex, while those of lathridiids may be convex or flattened, depending on the species. Most of them are unable to fly.
The antennae of lathridiids are 8 to 11-segmented, and have 1 to 3-segmented terminal clubs. The antennae of cryptophagids are always 11-segmented, and usually have loose, 3-segmented clubs, but in a few species these clubs are 2 or 4-segmented. The tarsi of lathridiids are usually 3-segmented, but in the males of some species, the tarsi of the first pair or first 2 pairs of legs may be 2-segmented. The tarsi of cryptophagids are 5 segmented, except for the males of some species, in which they have 4 segments. Thus, the number of tarsal segments is a good criterion for the separ'ation of the 2 families (Hinton, 1945).
The 5 species were collected 3 months after the apartment was plastered.
According to Hickin (1964), 48 species of lathridiids and 80 species of cryptophagids were found in Great Britain. In buildings he checked, the most common lathridiids were Aridius nodifer (Westwood), Thes bergrothi (Reitter), Corticaria serrata (Paykull), and Lathridius minutus (L.). The most common cryptophagids were Cryptophagus acutangulus Gyllenhal, C. cellaris (Scopoli), and C. distinguendus Sturm.
Microgramme filum (Aubé) (= Cartodere) (figure 333) was considered by Hinton (1941) to be the lathridiid most commonly found in buildings in Europe as a whole. It is also distributed throughout North Africa and North and South America.
The adult beetles are 1.2 to 1.6 mm in length, brownish, and have 2-segmented antennal clubs, whereas other species of this genus have 3 segments in the clubs. Hindwings are lacking in all species of Microgramme. Mature larvae of M. filum are 1.7 to 2 mm long, whitish, and have 3 segmented antennae, the second segment twice as long as the first. The pupae are white, and 1 mm long.
Hinton observed that 2 females laid a total of 20 eggs. The shortest life cycle at 75 °F (24 °C) was 36 days. At 65 °F (18 °C), a complete life cycle required about 54 days, and at lower temperatures might take as long as 5 months. The life cycles of 4 lathridiid species investigated in the United States varied from 12.8 to 28 days, and averaged 21.2 days at a mean temperature of 74.6 °F (23.7 °C) (Kerr and McLean, 1956). Microgramme filum was found in such environments as damp, moldy warehouses and cellars; damp areas near water taps; around leaky windows; under moldy wallpaper and moldy papier-mâché dishes; in damp stored wheat, corn, and rye; in boxes containing dried beer yeast; on moldy bread; and in many herbaria. Microgramme arga (Reitter) (= Cartodere) is similar to M. filum, but can be distinguished by having 3 instead of 2 segments in the antennal clubs and by having larger eyes. It is widely distributed, occurring in Europe, North Africa, and North America (Hinton, 1941).
Alphitophagus bifasciatus (Say) the twobanded fungus beetle, is a reddish-brown tenebrionid, with 2 wide black bands across the elytra. It is 3 mm long, elongate-oval, and convex. Outdoors it normally feeds on fungi growing on moist trees, but indoors it infests fermenting or decayed cereals and cereal products. It is cosmopolitan in distribution, and occurs in coastal California and Oregon (Essig, 1926).
Alphitobius diaperinus (Panzer), the lesser mealworm (Tenebrionidae) (figure 182, chapter 7) is also attracted to damp and moldy cereal products and spoiled foods. (See chapter 7, under "Insects Infesting Broken Grain," for a few more data.)
Ahasverus advena (Waltl), the foreign grain beetle, is a cosmopolitan cucujid, with projections at the anterior corners of the prothorax. It feeds on molds on damp grains, bread, biscuits, and other farinaceous materials, as well as dead insects that may be found in or on them.
Mallis (1969) reported the lathridiid Microgramme arga from ground cereals in Oregon, on the walls of a house and in a drugstore in Ohio, on heads of wheat in a field in Texas, and in an old brick house in Pennsylvania that had just been remodeled into apartments. The insects were found in June on walls that had been plastered 3 months before the infestation. They were seen around the windows and near a light fixture in the ceiling. The new plaster was apparently not completely dry at the beginning of the infestation, and high humidity caused by heavy rains kept the walls from drying out, thus encouraging the growth of molds. By late summer, the beetles had disappeared.
In Los Angeles, California, lathridiids, cryptophagids, and psocids were found in one plastered apartment building soon after the first apartments were occupied. A few of the beetles could be found in the building as long as a year after its completion. The adults were generally found at lights or windows. In one of the apartments just discussed under the heading, "Some Common Species," 3 months after occupancy, many lathridiids, cucujids, and a few cryptophagids and mycetophagids were collected. The apartment had been sprayed earlier for "plaster beetles," and hundreds had already been killed.
Fungicides such as Cunilate (copper-18-quinolinolate) and G-4 (dichlorophene) (NPCA, 1957), or 2% formaldehyde in petroleum distillate (Busvine, 1966), can be sprayed onto moldy areas, taking care to avoid contamination of foods. Fumigation of a building is rarely warranted for an existing fungus beetle infestation, since it provides no residual protection against reinfestation. Aerosols are convenient, and may kill the beetles contacted, but not those emerging later from concealed locations. Longer-lasting insecticidal residues can be obtained with sprays containing 2% chlordane, 1% lindane, or 0.5% dieldrin, provided the sprays are applied where the beetles can contact the residues, such as in the vicinity of moldy materials and about lights and windows where they congregate. Wall voids and other places difficult to reach with sprays can be dusted, using 5% chlordane, 1% lindane, or 1% dieldrin, adding 3% G-4 (dichlorophene) if a fungicide is desired in addition. Thorough milling to form a fine dust that will drift well into concealed areas should improve the mixture (NPCA, 1957).
Psocids are soft-bodied insects, the immature forms of which resemble the adults in form and structure. They are gray or light brown, winged or wingless, with a large abdomen, a narrow thorax, a large head, and long, many-segmented antennae. The outdoor species have wings, but are weak fliers. Their wings are held rooflike over the body, and are often marked with a pattern of some sort. The pearly-white eggs are relatively large, being about one-third the size of the adult insect. They are laid singly, and adhere to the surface upon which they are deposited.
Psocids can be serious pests of stored foods under excessively humid conditions. A key was developed to help identify 5 species commonly infesting stored foods in the United States: Trogium pulsatorium, the larger pale booklouse, which has 3 distinct thoracic segments (the other 4 species have only 2); Liposcelis bostrychophilus, the banded psocid, which has 7-faceted eyes and a brown head and body; L. paetus Pearman, the warehouse psocid (figure 335), which has 2 to 4-faceted eyes, a brown head, and yellow body; L. entomophilus (Enderlein), the grain psocid, which has 2 to 5 large pronotal bristles; and L. terricolis (Badonnel), the "booklouse" (figure 335), which has only 1 large pronotal bristle. [Liposcelis bostrychophilus and L. paetus do not have large pronotal bristles (Scott, 1963b).]
Biology. The cereal psocid, Liposcelis divinatorius, reproduces parthenogenetically (males are not known). In one investigation, the life cycle averaged 24.4 days from June to August, with an average of 57 eggs deposited. During cold weather, the adults died, and the eggs hatched in the spring. In winter, only 21 eggs per female were produced on an average, the preoviposition period was 45 days, and the life cycle was 110 days (Ghani and Sweetman, 1951). There may be 6 to 8 generations per year (Candura, 1932). In another investigation, the period from egg to adult required about 1 month at a temperature of 80 °F (27 °C) and relative humidity of 65%. There were 3 molts. After a preoviposition period of 2 to 3 weeks, eggs were laid at the rate of about 1 every 12 hours until perhaps 75% of the total were laid. Then, a long period followed when only an occasional egg was deposited. An adult life of over 3 months was observed (Finlayson. 1932). In England, Trogium pulsatorium was found to have only 1 generation a year and to overwinter in the nymphal stage, whereas Liposcelis divinatorius bred continuously, and was found in all stages, even during the winter months (Pearman, 1928).
Desiccated L. divinatorius recovered even more rapidly. Insects that had become flattened and lethargic from desiccation became turgid and active within 2 or 3 hours when moisture was restored, and began laying eggs (Finlayson, 1932). With food available, females of L. rufus died within 2 to 3 weeks at all RH's below 58%. Other species were even less resistant to desiccation. Females of L. knullei Broadhead and Hobby lost water twice as fast as L. rufus, and died within 1 week at all humidities below their critical level. Liposcelis bostrychophilus survived only 10 days, and egg-laying ceased, below the critical equilibrium humidity (Knülle and Spadafora, 1969).
After having moved from 2 apartment buildings in succession because of psocid infestations, tenants in a beach community in southern California moved to a third building, but first they had their overstuffed furniture, clothing, blankets, linens, and other personal belongings fumigated to avoid the possibility of a third occurrence of what had become a traumatic experience.
Besides being household pests, psocids resemble fungus beetles in occasionally infesting granaries, warehouses, herbaria, insect collections, libraries, stored foods, and the nests of birds and insects (Finlayson, 1932; Linsley, 1942, 1944; Broadhead and Hobby, 1944). The 2 household pests, Liposcelis divinatorius and Trogium pulsatorium, have been reported as predators of eggs of the Angoumois grain moth, Sitotroga cerealella (Finlayson, 1932), and Liposcelis bostrychophilus was observed to feed on the eggs of the Indian meal moth, Plodia interpunctella (Lovitt and Soderstrom, 1968). In one test, L. bostrychophilus consumed 71 and 72% of the eggs when other food was absent or present, respectively.
Mallis (1969) cited the results secured by a pest control operator who thoroughly sprayed, with 2% chlordane in base oil, all the exposed woodwork of a 6-month-old house that had been built with green lumber. He obtained excellent control of psocids. In view of the widely recognized efficacy of dichlorvos, Mallis suggested that a 0.5% solution of this insecticide should also be tried in psocid control.
Springtails are found outdoors in moist situations, usually feeding on algae, fungi, and decaying vegetable matter. They are among the most troublesome swimming pool pests. In southern California, Hypogastrura armata (Nicolet) (figure 336, E) appears to be the one most frequently involved. This is a common species of world-wide distribution. It is dark gray to black dorsally, light gray ventrally, and with a reddish hue on the head, antennae, and legs.
If their environment becomes dry, then in the course of their active crawling in search of moisture, springtails may invade the home, entering through window screens, open doors, vent pipes, or with merchandise or ornamental plants. They may be attracted to light, entering through windows or under doors. After a hot day, they may swarm over the side of a building in tremendous numbers, increasing the chance of indoor infestation. After entering a house, they crawl about, and are often trapped in sinks, washbasins, and bathtubs. They are most commonly found where there are sources of moisture, as in the kitchen and bathroom, where they hide in very small cracks and crevices. They may also occur in damp wall voids. In some homes, potted plants serve as sources, the springtails coming from the damp soil (Scott et al., 1962; Scott, 1966c).
Ideal conditions for springtails result from high humidity in conjunction with excessive organic debris. In addition to whatever nutritive material that may be present in the organic matter, mildew spores can form, contributing further sustenance. Springtail infestations can be suspected whenever mildew odors are detectable. Infestations tend to increase during hot, humid weather, and decrease during cold weather when the heating system dries the air and the building structure. Even during the drier periods, however, springtails may be found in great abundance around the insulations of steam and water pipes (Scott et al., 1962; Scott, 1966c).
A pictorial key has been prepared to help identify the common springtails of the United States (Scott et al., 1962).
The mold mite, Tyrophagus putrescentiae (Schrank), is becoming increasingly common as a household pest, causing allergic reactions.
The larvae are usually slender, 12 segmented, footless, with 8 pairs of spiracles, smooth and whitish, but with brown or black sclerotized heads. They infest fungi, damp soil, litter, decaying vegetation, or decayed wood. Under optimum conditions, the larvae can develop through all 5 instars in 6 to 8 days. Some species form silken cocoons on or in the ground in which to pupate, and the adults emerge in about 3 days. Certain species are pests in mushroom cellars (Essig, 1926; Lauret, 1962; Curran, 1965).
Megaselia rufipes (Meigen) is a cosmopolitan species that is commonly encountered throughout the United States. It is black or dull brown, with yellowish or brown legs.
Megaselia scalaris (Loew) is a tropical and subtropical species and Dohrniphora cornuta (Bigot) is a cosmopolitan species; both are common in California.
Description. The adult moth is dark brown, with uneven, lighter markings across its broad wings. When at rest, the male measures 13 mm and the female 16 mm in length. The female is 19 or 10 mm across at the tips of the folded wings (figure 339). The mature larva is naked, shiny dark brown to black, and is about 20 mm long. It is ringed with interrupted annulations that give it a wrinkled appearance (Pence and Hogue, 1957).
Habits. This moth occurs in the dark, damp locations where dry-rot fungus develops. In one instance in which the insects originated in mycelial growth of fungus under a sink, where leaky tile grouting permitted moisture to penetrate the wood beneath, the larvae were found in much of the house, but particularly in the kitchen and bathroom, and migrated extensively before pupation. In another instance, this species was found infesting a garage adjoining a home. A pile of damp fabrics stored in the garage had developed a growth of fungus, providing food for the larvae. A laboratory experiment demonstrated that these larvae could thrive on a diet consisting only of the mycelium of Poria incrassata. They fed directly on fragments of dry mycelia placed on a damp substrate. The fragments were bound together in dense webbing (Pence and Hogue, 1957).
Description. The meal moth has a wingspread of about 25 mm. The base and apex of the forewing are reddish brown, with the middle portion pale, but bordered on each side by a wavy, white line. A row of black dots occurs along the posterior margin. The dirty-gray larva, with a dark head and prothoracic shield, is about 25 mm long when full grown (Linsley and Michelbacher, 1943).
Habits. In one instance, where the moths infested all the rooms of a house and persisted despite attempted control measures, a mass of webbed and matted straw was found on moist soil in the crawl space under the building. The straw was teeming with adults and immature stages. The moths had found their way into the rooms by entering forced-air heating vents and pipe openings.
The infestation stopped after the straw was removed (Berns, 1958).
In common with Aglossa caprealis, the moth can reach full development on a diet consisting solely of dry-rot fungus (Pence, 1956a).
The commonly used English name, "woodlouse," is more appropriately applied in Europe, where these isopods occur commonly in wooded areas far from human habitations, than it is in North America.
In the United States, sowbugs and pillbugs may be found in and around homes wherever there is a combination of excessive moisture and an abundance of decaying organic matter. The majority of isopods are aquatic forms, and obtain their oxygen through gills, but the sowbugs and pillbugs breathe by means of tubelike invaginations or pseudotracheae, enabling them to live on land. However, the pseudotracheae open to the exterior by a single pore which lacks the spiracular closing device possessed by other arthropods. Some respiration also takes place through the integument of the body (Cloudsley-Thompson, 1968).
These land crustaceans are not so well adapted as insects for controlling water loss, for they not only lack a closing device for the respiratory system but also lack the epicuticular wax layer that protects insects from excessive transpiration, even in dry environments (Edney, 1957; Barnes, 1963; Cloudsley-Thompson, 1968). Therefore, these isopods must remain during the day beneath objects on damp ground, or even bury themselves well beneath the ground, if necessary, to avoid desiccation. They may also huddle together in masses to reduce the evaporation rate, and travel about during the night, taking advantage of the lower temperature and higher humidity. Moist food and water to drink also help to replace the water lost by integumentary evaporation.
Sowbugs and pillbugs normally live outdoors, and sometimes injure tender young plants or their roots. Their scavenging habits are indicated by an observation that pillbugs in large numbers almost completely devoured a dead rat and ate the flesh off a peach pit (Pierce, 1907). They sometimes become accidental intruders into houses, where they do no damage and cannot survive. Slab floors and sliding doors have increased the likelihood of occasional intrusions of these isopods into the home.
Description. Sowbugs (figure 341) are up to 13 mm long, dorsoventrally flattened, oval, and have a broadly convex, hard exoskeleton composed usually of 10 freely articulating tergites that tend to project laterally. The segments of the thorax and abdomen are usually about the same width, and are not clearly demarcated dorsally. The adults are dark gray to slate color above, with a wide, dark, longitudinal median band becoming lighter in color laterally, and they are light gray beneath. They have well-developed, sessile, compound eyes, well-developed antennae, and 7 pairs of legs, a pair for each thoracic segment (Barnes, 1963). Porcellio scaber differs from P. laevis in having transverse rows of small tubercles covering the head and body dorsally (CloudsleyThompson, 1968).
Biology. The eggs hatch in a brood pouch (marsupium). During the last weeks of a gravidity of about 50 days, there may be eggs in the marsupium as well as young sowbugs ready to emerge. In investigations by Hatchett (1947) in Michigan, 24 young per brood were born on an average, but as many as 88 young per brood have actually been recorded (Verhoeff, 1919, 1920). There may be 1, 2, or 3 broods per year, but usually 2 (Hatchett, 1947). Adult sowbugs may live about 2 years.
Biology. The biology and habits of pillbugs are similar to those of sowbugs. Pierce (1907) noted that pillbugs were white and had 6 pairs of legs when they left the marsupium. Within 24 hours they molted, and still had 6 pairs of legs. The next molt occurred between the fourteenth and eighteenth days, and the isopods then had 7 pairs of legs. There was no regularity in the time of molting after the first molt; the time depended on the food supply. Pierce found that females about 7 mm long could reproduce. The largest pillbug he noticed was 15 mm long, and he believed it to be several years old. From 29 to 79 young per brood were recorded in Texas (Pierce, 1907); 5 to 62 (average 28) in Michigan (Hatchett, 1947); and 48 to 156 in France (Vandel, 1939). There could be from 1 to 3 generations per year, depending on the mean temperature of the region.
Residual pesticide treatments may be applied to and near foundation walls, to damp areas surrounding or near the building, and to the crawl spaces underneath it. Most of the common garden insecticides, such as carbaryl, chlordane, diazinon, malathion, and propoxur (Baygon), applied as sprays or dusts, are effective. Treatment of peat moss, wood chips, and redwood bark used as mulches in the garden is particularly important. Subsequent sprinkling will carry the insecticide down into the soil where the crustaceans hide. Known points of entry into the home for sowbugs and pillbugs should be sealed off. These pests can not only be killed with household insecticides, but can also be swept or vacuumed away. Most of them will be dead by the time they are discovered for, as already stated, they cannot survive for more than a day or two away from moist areas.
Description. Millipedes are long, cylindrical, many-jointed, wormlike arthropods. The mature forms vary from 10 or 15 to 100 mm or more in length. Most of them are blackish or shades of brown, but some species are red, orange, or have mottled patterns. They have 2 body regions. The head has a pair of short, 7 segmented antennae, at least 2 pairs of mouthparts, and usually eyes. In the body, the first segment behind the head bears no legs, while the next 4 segments (the next 3 in a few species) each have 1 pair of legs. All other segments except the last (in some species except the last 2 or 3) have 2 pairs of legs. The segments with 2 pairs of legs are diplosegments, derived from the fusion of originally separate segments. "Spiracles" leading into tracheae open above the coxae. However,.the tracheal system has no closing mechanism such as the spiracles of insects (Miley, 1930). The integument is hard, rounded above, and flattened below. Like the integument of isopods and chilopods, it possesses no protective lipid barrier. The absence of surface lipid, along with the inability to close the tracheal openings, makes diplopods particularly susceptible to a lethal rate of water loss in dry environments.
The two pairs of legs on most segments, particularly well shown in figure 342A, distinguish millipedes from centipedes. Most millipedes are rounded above, whereas centipedes are flattened. Millipedes crawl very slowly, whereas centipedes crawl quite rapidly. However, the gait of millipedes exerts a surprising pushing force, enabling the animals to force their way through humus, leaves, and loose soil (Barnes, 1963).
Biology. Millipedes lay from 20 to 300 eggs in nests in the soil. The eggs of most species hatch in several weeks, and the newly hatched young usually have only the first, 3 pairs of legs and not more than 7 segments. Millipedes have a simple metamorphosis, going through a number of molts during each of which additional segments and legs are added. In many species, there are 7 larval instars. Many species of millipedes reach sexual maturity in 2 years, but some require 4 or 5 and will then live several more years. Adults generally overwinter in the soil. In some orders, the millipedes build molting chambers in the soil, similar to the egg nests, for after each molt the animals are helpless against predators. Millipedes usually eat their cast skins to restore lost supplies of calcium, and if they do not do so, further development is abnormal (Cloudsley-Thompson, 1968).
Protective Devices. Millipedes do not possess venom-bearing claws (toxicognaths) as do centipedes, but they do have certain protective devices. The species of one order of millipedes (Oniscomorpha) can roll up into a ball like the pillbugs, protecting their soft underparts.
In the Colobgnatha, Polydesmoidea, and Juliformia there are repugnatorial glands, either 1 per segment on all but the more anterior segments or on more or less alternate segments. They open on the sides of the tergites, and secrete a mixture of hydrocyanic acid, iodine, and quinone, a brown or white liquid with an iodoform odor. It is believed to be toxic to other small animals, and is reported to be caustic to the human skin and to cause vesicular dermatitis. Most species exude the liquid slowly, but some can discharge it as a spray. Some of the tropical species can produce a severe dermatitis and possibly blindness (Halstead and Ryckman, 1949; Barnes, 1963).
Back (1939) described migrations of millipedes in the eastern United States in which they swarmed over basements and first-floor rooms of houses in great numbers. Sometimes they crawled up walls and dropped from ceilings. These migrations occurred most often in the fall. He considered the migrations to be caused by an urge to seek hibernating quarters, although sometimes heavy rains raised the water level in the soil and forced the millipedes to seek shelter elsewhere. Back found that homes in wooded areas with virgin soil, still filled with quantities of decaying vegetation, were particularly susceptible to infestation. As many as 700 millipedes entered a room in a single evening.
Many millipedes, as well as sowbugs and pillbugs, drop into swimming pools, and are usually more common problems in this respect than are insects. Also, sliding doors in houses with concrete slab foundations allow the entry of many millipedes, centipedes, sowbugs, and pillbugs.
Description. Oxidus gracilis is one of the "flatbacked" millipedes (order Polydesmoidea), in which the somites are dorsoventrally flattened. The 20 postcephalic somites bear 30 and 31 pairs of legs in the males and females, respectively. The adult males are about 19 mm long, and the females, about 21 mm. These millipedes vary in color from the creamy white of recently molted specimens to deep chestnut brown or black in the oldest individuals (Causey, 1943).
Orthomorpha coarctata is almost indistinguishable from Oxidus gracilis. Two other species common in California are Julus hesperus Chamberlin and Tylobolus claremontus Chamberlin (figure 342, A and B).
Life Cycle. As with most tropical animals, Oxidus gracilis has no annual breeding season. Oviposition was found to occur during any month of the year if the temperature was maintained above 22° C (71° F). Eggs were deposited in small, rough cavities, 7 to 15 mm below the soil surface, in clutches, that varied from 14 to approximately 300. The larvae of each instar differed in the numbers of somites and legs, in size, and in density of pigmentation. Sexual maturity was reached in the eighth instar. Five millipedes reared from eggs collected in September passed through the 7 larval instars in 148 to 177 days at "heated-room" temperatures (Causey, 1943).
Orthomorpha coarctata laid eggs in the soil in holes that were 20 to 40 mm deep and 5 to 7 mm in diameter. There were 25 to 300 eggs per clutch. The.period from egg to adult ranged from 119 to 187 days in a rearing room. There were apparently 2 generations per year (Bennett and Kerr, 1973).
Habits. In the limited areas where 0rthomorpha occurs, it is a greater problem than Oxidus. It apparently breeds in the thick thatches of St. Augustine grass (Stenotaphrum secundatum) in southern Florida that contain large amounts of decaying organic matter on which it feeds. The greatest migration activity was observed from about 8 to 11 in the forenoon, but very little occurred in the afternoon hours until sunset. Migration activity about one-third of that noted in midmorning continued throughout the night, from 10 p.m. to 7 a.m. The millipedes were commonly observed on patios, outside walls, and foundations of buildings. Their numbers increased during the summer and fall months, and reached pest levels from late September to early December (Bennett and Kerr, 1973).
Oxidus gracilis appeared to breed only in wild and overgrown areas where there was much decaying leaf litter. From these places, it occasionally dispersed to nearby habitations. It fed on decaying organic matter, but could not be induced to feed on tender, living plants (Causey, 1943; Bennett and Kerr, 1973).
Fig. 333. A fungus beetle, Microgramme filum. A, larva; B, pupa; C, adult. (From Hinton, 1941.)
Fig. 334. A house-infesting psocid, Psyllipsocus sp.
Fig. 335. Two psocids commonly found on stored foods under excessively humid conditions. Left, warehouse psocid, Liposcelis paetus; right, booklouse, Liposcelis terricolis. (From Scott, 1963b.)
Fig. 336. Building-infesting springtails. A, Onychiurus armatus Tullberg; B, Isotomodes tenuis Folsom; C, Folsomia sp.; D, Proistoma sp.; E, Hypogastrura armata (Nicolet); F, Lepidocyrtus sp.; G, Entomobrya atrocinta Schött; H, Orchesella sp.; I, Seira platani (Nicolet); J, Podura aquatica L. (From Scott, 1966c.)
Fig. 337. Two springtails commonly found in damp locations in and around buildings. Top, Onychiurus armatus; botton, Entomobyra atrocinta.
Fig. 338. A sciarid fly occasionally found in damp locations in buildings.
Fig. 339. A pyralid fungus moth, Aglossa caprealis. Adult and larva.
Fig. 340. A tineid fungus moth, Nemapogon sp.
Fig. 341. Isopods that may invade the home. Top sowbugs, Porcellio dilatatus; bottom, pillbugs, Armadillidium vulgare.
Fig. 342. A, millipede, Julus hesperus; B, millipede, Tylobolus claremontus; C, centipede, Scolopendra polymorpha.
Fig. 343. The greenhouse millipede, Oxidus gracilis.