Slugs and snails hide during the day in damp places, such as under boards, rock piles, low-lying shrubs, damp refuse and litter, and dense vegetation of all kinds. Beds of ivy are particularly conducive to heavy infestations of these gastropods. They may be seen during daylight mostly in the early morning and particularly after a rain, or if the lawn and adjacent vegetation have been sprinkled the preceding day. At that time, the pests are generally on their way back to their daytime hiding places, avoiding dry or dusty areas or sharp objects if they can. Snails may sometimes be seen at midday, usually firmly attached to walls, fences, tree trunks, or their food plants. When dry conditions prevail, they seal the opening of the shell with a mucous secretion that becomes a parchment-like sheet called the operculum; this finally becomes hard and leathery. They can then exist in a dormant condition for as long as 4 years. With the return of favorable conditions, the operculum is rasped away by the snail's mandible. Snails can survive lower humidities and lower temperatures than slugs (White and Davis, 1942).
Snails and slugs are garden pests, particularly of tender, young seedling plants and of berries and other fruits. They may cause only surface scars, or may make deep holes in the fruit, besides covering it with the mucus they deposit when crawling.
The longnecked slug, Deroceras laeve (Müller), is an almost cosmopolitan species that invades gardens with D. reticulatum, particularly in the San Francisco Bay region. It is about 32 mm long, and is usually various shades of amber, without spots or markings, but is sometimes blackish, with the head and tentacles smoky. In live individuals, the mantle appears to have a circular orangebrown area. A characteristic feature is its long neck which, when extended, is almost as long as the mantle.
The gray field slug, Deroceras gracile (Rafinesque) or Agriolimax campestris (Binney), considered to be a form of D. laeve by Pilsbry (1948), occurs in all parts of the United States. It is a small species, seldom more than 25 mm long, and is buff to almost black. The slime is clear, not milky as in D. reticulatum. According to A. G. Smith (correspondence), there have been many introductions of the European D. laeve into the United States, particularly into central California, and it is these that are called "longnecked slugs." Smith has found the indigenous form of D. laeve, as recognized by Pilsbry, in many places all through the Sierra Nevada and also in his garden in Berkeley. He has never found the "longnecked" race in his garden, although it is prevalent in Golden Gate Park in San Francisco and in nurseries and cultivated areas in Alameda and Contra Costa counties.
The banded slug, Lehmannia poirieri (Mabille) Limax marginatus (Müller)] (figure 351, C and D), another European species, may attain a length of from 50 to 75 mm, and has a general light brown color, with parallel, longitudinal, gray, dark-brown, or black bands on the mantle. There are 3 such bands in immature slugs, but the middle band tends to disappear with approaching maturity. These slugs are basically fungus-feeders, but they are also among the principal citrus pests, and will feed on garden plants and underground tubers.
The spotted garden slug, Limax maximus L., is the largest of the European "gray" slugs introduced into western America, exceeded in size only by the indigenous Agriolimax species (Hanna, 1966). It prefers human habitations and, although like other limacids it is a fungus-feeder by preference, it often causes injury to garden plants. It is yellowish gray or brown, with large, irregular black spots, and is usually about 100 mm long, but may reach a length of 200 mm. The mature specimens have a dark-spotted mantle, but in immature slugs these spots may be united into bands.
The tawny garden slug, Limax flavus L., is widely distributed in the eastern and southern parts of the United States, and was recorded in California as early as 1903. It is a large species, 75 to 115 mm long, and is exceeded in size only by L. maximus among the introduced European species (Hanna, 1966). It is yellowish green, with yellow spots, and exudes a yellowish slime when disturbed. Its mantle consists of a series of concentric grooves, giving it a reticulate appearance, and the ocular tentacles are bluish. This slug is gregarious, and may be found under garbage cans, in basements, wells, drains, and under doorsteps. It may be found in nurseries, and also does some damage to garden plants.
The greenhouse slug, Milax gagates (Draparnaud) (figure 351, E and F), was introduced into North America as early as 1872. It is very destructive to nursery, garden, and field crops in California, and its burrowing habits make it a pest of root crops. It may attain a length of 40 to 70 mm, is dark gray or black, has an oval or diamond-shaped groove on the center of the mantle, and has a prominent, sharp, dorsal keel extending back the entire distance behind the mantle. The keel is especially conspicuous when the body is contracted (Lange, 1944).
The largest and most widely distributed of the giant slugs is the giant yellow slug, giant redwood slug, or banana slug, Ariolimax columbianus (Gould). It occurs in parts of Alaska, west of the Cascade Mountains in British Columbia, Washington, and Oregon, in California south to the Salinas Valley on the coast, and at least as far south as Tuolumne County on the western slopes of the Sierra Nevada. The adult of this very large slug weighs from 35 to 72 grams, and its foot varies from 18.5 to 26 cm in length when fully extended. The ground color is described as "deep, olivaceous green, tan-green, ochraceous, ochraceous-yellow, slate-green, or intermediate shades," with the mantle of the same color. According to Lange (1944), this species occasionally invades gardens to feed on vegetables and other plants. There is also a form that is spotted or blotched with black. The ground color of A. columbianus, including the mantle, is very variable, but never attains the light-yellow color of the other species of the genus, which are less variable. The color of individual slugs will change with age and alterations in food, moisture, and light. There is also a smaller and more slender subspecies, A. c. stramineus Hemphill, distributed south and west of the Salinas Valley, from the Monterey peninsula to at least Ventura County and in Santa Cruz and Santa Rosa islands. It weighs 20 to 27 grams, and its foot is 13 to 16 cm long. Its ground color is vitreous lemon-yellow or light straw-color (Mead, 1943; Pilsbry, 1948).
Ariolimax californicus Cooper occurs in San Mateo County and northwestern Santa Clara County in coastal central California. It is a smaller species than A. columbianus, the adults weighing 25 to 42 grams and having a foot length of 17.5 to 20 cm. The ground color, including the mantle., is vitreous butter-yellow, rarely ochraceous yellow. This slug occasionally invades vegetable fields and gardens, but usually does not do extensive damage (Lange, 1944). Ariolimax c. brachyphallus Mead occurs on the San Francisco peninsula. It is the smallest slug of the genus, weighing 17 to 23 grams, and has a foot length of 12.5 to 15 cm. Its ground color is ochraceous or ochraceous brown, and its mantle is usually ochraceous yellow and rarely the same color as the remainder of the body.
Ariolimax dolichophallus Mead is limited to coastal central California, from northern Santa Cruz and western Santa Clara counties to the Salinas Valley. It is a slender species, with adults weighing 20 to 39 grams an a foot length of 15 to 18 cm. Its ground color, including the mantle, is opaque butter-yellow. It obtains its name because of its extremely attenuate apical phallus (copulatory organ) being very long occasionally it may be longer than the slug itself (Mead, 1943; Pilsbry, 1948).
Description. The shell of this snail (figure 352) is grayish yellow and brown. The brown is usually in 5 interrupted bands, the second and third ones being ordinarily confluent, giving the appearance of a single band. All the bands may be united in some individuals. When fully developed, the shells have 5 or 4.5 whorls, and are 2.5 cm or more in diameter. The shell's form is that of a dextral or right-hand spiral, the sinistral or left-hand aspect being very rare. The body is light to dark gray, and is about 6 cm long when fully extended. (Basinger, 1931).
Life Cycle. Oviposition usually occurs within 3 to 6 days after fertilization. The snail selects a spot where the soil is damp, and prepares a nest for the eggs in the ground at a depth of 2.5 to 4 cm (figure 353). The eggs are white, somewhat translucent, spherical, and about 3 mm in diameter. The egg mass contains an average of 86 eggs. After ovipositing, the snail closes the opening of the nest with a little mound of earth and excrement to conceal its location. The young snails have shells of somewhat more than 1 whorl when they hatch. They usually remain in the nest for 2 to 4 days, then work their way to the surface. Two years are required to reach maturity.
For many years, a bait containing 5% metaldehyde (C2H4O)n or 3.25% metaldehyde and 5% of an arsenate has been used for the control of slugs and snails. The bait containing only metaldehyde is particularly effective against slugs and during the warmer periods of the year. The arsenate increases its effectiveness under adverse conditions or against snails, providing greater toxicity, while the metaldehyde continues to act as an attractant. The bait should be applied every 7 to 10 days until control is accomplished. Also available is a 20% spray concentrate which is diluted with water to produce a 0.25% spray.
The carbamate insecticide Zectran® (table 1, chapter 2) is also an effective molluscicide, and is available as 2% granular bait or a 2E (2 lb per gal or about 1 kg per 4 L) emulsifiable concentrate. The bait kills the pests in 3 to 5 days and lasts for about 2 weeks. It should be reapplied in about 3 weeks. The emulsifiable concentrate is diluted to make a spray of 0. 1% toxicant. It is said to be more effective than metaldehyde spray, even though it kills more slowly.
The most recently developed molluscicide is the carbamate insecticide Mesurol®, 3,5-dimethyl4-(methylthio)phenol methylcarbamate, also sometimes expressed as 4-(methylthio)3,5-xylyl methylcarbamate. (See table 1, chapter 2.) Mesurol, in both wettable powder and pellet formulations, was found to be superior to metaldehyde against the gray garden slug, particularly under damp or cold conditions (Wouters, 1970). It is available as a 20% granular bait, and is said to be the most rapid-acting of the molluscicides, giving good control in 1 or 2 days. Only a single treatment is usually required (NPCA, 1973).
Live specimens of T. sylvaticus are brownish black, and approximately 8 mm long when mature, but turn red when they die (plate VIII, 7), and this is the condition in which they are usually seen by the homeowner, for they do not live long after entering a house. They may be found in coastal southern California in and on the ground in damp places, particularly under ivy, where they sometimes occur in enormous numbers, jumping about like fleas.
Although terrestrial amphipods require damp locations, excess moisture forces them to seek drier locations, and they may then become accidental intruders into the home. The lack of a waterproof wax layer which forces them to seek damp locations is also a hazard to them if their environment becomes too wet, for they are not only susceptible to desiccation but also to a lethal rate of water uptake by osmosis. The author observed after an unseasonable early rainfall of 0.3 in. (8 mm) in September, 1963, that T. sylvaticus migrated away from an ivy patch, and large numbers found their way into a near-by house. These were dead the following day, apparently, as observed by Mallis (1942, 1969), finding their new environment too dry. Again, following early rain in October, 1966, a local resident brought in large numbers of the amphipods, found in his home, for identification. During the following winter they became so troublesome that he sprayed his ivy with a 0.5% diazinon emulsion and found it to be an effective control measure.
They eat insects, both living and dead, particularly aphids, but also eat vegetable matter, and can be injurious to tender plants. Insects are seized by the leglike pedipalps, passed to the chelicerae, macerated, and the liquids are consumed, along with some coarse particles. Phalangium and Liobunum are familiar genera.
Biology. The adult clover mite (figure 355) averages about 0.75 mm in length, and may be rusty brown, olive green, or dark red. The best distinguishing feature is the pair of front legs that are longer than the body and about twice the length of the other legs. The young stages are bright red. Ordinarily, the smooth, spherical, red eggs are laid on trees and other vegetation throughout the summer and fall. Those laid in late fall hatch the following spring, and may sometimes be seen in such numbers on the limbs of trees, particularly at crotches, as to give the appearance of brick dust. They are also sometimes seen on the foundations or outer walls of buildings.
Clover mites reproduce parthenogenetically, that is, without fertilization. Males have not been found in the United States, and only rarely in a few other parts of the world. A female will lay about 70 eggs. This species has a larval stage, 2 nymphal stages (protonymph and deutonymph), and an adult stage. About 1 month is ordinarily required to complete a generation outdoors, the optimum temperature for development being 69 °F (21 °C). Above 75 °F (24 °C), the eggs become dormant, and they are also inactive below 40 °F (4 °C). In Illinois and Pennsylvania, the form of clover mite that infests dwellings becomes dormant during May and remains so until September (Snetsinger, 1967). According to Spear (1954), in the eastern states the mites may be found in infested houses from November until May or June. They can invade a house in enormous numbers; 250,000 were estimated to be present at one time on the floor of a bedroom.
The period when the mites are most likely to enter dwellings varies with the climate - in April or May in Pennsylvania, but earlier farther south and later farther north. In California, pest control operators receive most of their calls for mite control in the spring months, with a secondary peak of activity in the fall. Infestations are usually most severe on recently occupied and landscaped property. After populations of natural enemies have had opportunities to become established, the mites become less of a problem. There are at least 62 species of predators that attack the clover mite. [Eight are spiders, 15 are mites, 5 each are thrips, anthocorid bugs, and mirid bugs, 15 are coccinellid beetles, and the rest are in other families and orders of arthropods (Snetsinger, 1960).] Also, the grass near the foundation is likely to be replaced by ornamental plantings, and the vigor of the remainder of the lawn decreases, both tending to reduce the mite population (Snetsinger, 1967).
Acaricides such as chlorobenzilate and ovex can be safely used around windows and doorsills Or similar points of entry. Treatments within the house give only temporary relief if no control measures are practiced outside (English and Snetsinger, 1957; Snetsinger, 1967). Inside residences, mites can be removed with a vacuum cleaner so as not to crush them and to avoid making the red smears that result if a cloth or brush is used.
Earwigs (order Dermaptera) feed on live or decaying vegetation as well as live or dead insects. When a female was offered living insect prey, she immediately grasped it in her forceps, and while still holding it, she turned her body in a half circle and ate the insect (Klostermeyer, 1942). Earwigs at times cause damage to cultivated plants, but can also become household pests by invading a home in large numbers and being severe nuisances.
Earwigs are medium-sized insects, ranging in the United States from 5 to 25 mm in over-all length. They are elongate and flattened, have a tough, shiny exoskeleton of various shades of brown, or are sometimes black. The mouthparts are of the biting type. The metamorphosis is gradual, usually with 4 or 5 nymphal instars. When wings are present, the first pair form very short, usually truncate, veinless, hard wing covers, making them resemble superficially the staphylinid or rove beetles. The second pair of wings are fanshaped, with a peculiar radial venation. When not in use, they are folded in a complicated fashion into a compact mass that is almost completely covered by the abbreviated wing covers. The body terminates in a pair of strong, movable forceps or pincers, those of the males being larger and more caliperlike. They are used for defense, capturing prey, probing the area inside a narrow crevice, and to a lesser extent for folding and unfolding the wings (Morgan, 1923; Essig, 1942). Morgan (1924), in an investigation of Labidura bidens Olivier, could find no evidence that the forceps were used in mating, as had sometimes been reported.
Earwigs are nocturnal in their habits, hiding during the day in moist, shady places under stones or logs, in cracks in the soil, or in almost any secluded place. Their ways are similar to those of cockroaches, including their gregarious nature, their habit of cleaning their appendages with their mouthparts (Bharadwaj, 1966), and the fact that they are repelled by dust (Crumb et al., 1941). Neither eggs nor nymphs are able to withstand prolonged desiccation.
The eggs were never known to hatch in the absence of the female, probably because it is necessary for them to be kept in a moist situation, and yet protected from mold. The care of the eggs includes "licking," turning as done by a hen, and frequent shifting of their position, now in a layer on the side of the cell and now, perhaps, in a heap at the bottom. In spite of her solicitude for them, the female will eat her eggs readily if conditions become too unfavorable or even if she is disturbed too much.For the first few days after the eggs hatch, the female keeps the nest closed. It is opened later, but she guards against intruders, using her forceps as weapons. She brings in food for the young, which remain inside or close to the nest until after their first molt (Fulton, 1924a, b; Crumb et al., 1941).
The female of the striped earwig, Labidura riparia, also remains with her eggs in a specially constructed chamber, grooming the eggs at intervals until they hatch 8 to 10 days later. She does not eat during the incubation period. The newly hatched nymphs remain in the chamber with the female for another 2 to 4 days. She will eat the nymphs if the nest is disturbed (Caussanel, 1970).
Description. Adult females, including forceps, are about 16 mm long. Some adult males are about the same size, but others are considerably larger. As with the Dermaptera in general, the males have larger and more caliperlike forceps (figure 356). With regard to the size of the forceps, the males are dimorphic, the forceps being about 3.5 mm long on some and 7 mm long on others (figure 358, F and H). Those with longer forceps usually have much larger bodies. The general color is dark reddish brown, with the head decidedly reddish and the wing covers, legs, and antennae paler. On each side of the dorsal aspect of the third and fourth abdominal segments (second and third visible segments) are the openings of glands that discharge small drops of liquid if the insect is picked up. This liquid is probably responsible for the peculiar odor of earwigs (Fulton, 1924a).
Habits and Life Cycle. Pairs of European earwigs dig into the soil in the fall, and usually hibernate in cells 3 or 4 cm beneath the surface. In observations made in mid-January, Fulton (1924a) found eggs in some cells and, when no eggs were present, the body of the female was full of them. The eggs are about 1 mm long, pale yellow or cream-colored, opaque, and broadly elliptical. As they develop they become larger, whiter, and more translucent. The males leave the cells in January, and can be seen in numbers until the last of April or May, when some reenter the soil with the females a second time. The females begin to leave the soil in April, most of them appearing on the surface by the middle of May, having spent about 7 months in the soil without food. Some of the females again enter the soil to deposit a second clutch of eggs. Thus, there may be 1 or 2 generations a year.
Under the climatic conditions at Puyallup, Washington, adults entered the soil for hibernation from the latter part of September to the last of October, the period of maximum entrance apparently depending on the advent of cool weather. Many males, an occasional female, and rarely a nymph remained above the surface throughout the winter. The average incubation period for winter egg masses was 72.8 days, and for the second or spring clutch it was about 20 days. There appeared to be about equal numbers of new males and females. In the field, the period required for the development of the 4 nymphal instars was about 68 days, while in the laboratory between 60 and 70 °F (16 and 21 °C), it was about 31 days (Crumb et al., 1941).
Few people have seen earwigs in flight, but Crumb's group observed as many as 20 flights in one day, mostly in bright, warm sunshine. An elevated object seemed to be necessary for takeoff, and the insects were able to rise and fly at least 30 ft (9 m).
Economic Importance. European earwigs are omnivorous, but prefer plants such as mosses, lichens, and algae as food. Some animal food seems to be required, and this includes insects, spiders, mites, and protozoa, alive or dead (Crumb et al., 1941). They occasionally do some damage to flowers, fruits, vegetables, ornamental shrubs, and trees, and have been known to feed on honey in beehives. Damage is small when compared with the numbers of earwigs that are sometimes present. In one investigation, digestive-tract analyses showed the diet to consist largely of lichens and pollen (Dimick and Mote, 1934).
The insects are most abundant in the gardens or homes of urban areas, and around buildings in rural communities. They tend to avoid cultivated or dry land, and sometimes invade houses in enormous numbers. Fulton (1924a) quoted thus from a correspondent:
Literally thousands and thousands of those bugs inhabited my premises last summer. They made it almost impossible to live in my home; they inhabited the sleeping porch till we had to leave it. They work mostly at night, but in the daytime might be found in kitchen drawers, and often burrow an inch into a loaf of bread. They crawl over ceilings at night and drop on the bed, or inhabit themselves in a person's clothing during the night, and while their bite has never proved serious, it is entirely uncomfortable.With regard to infestations in Oregon, Fulton stated that it was almost impossible to keep European earwigs out by the use of screens, and that they had become so annoying in some districts that property values had depreciated considerably. There were successive importations from Europe of a tachinid parasite, Digonichaeta setipennis Fall, from 1924 to 1929 in Oregon and California, and as high as 38.4% parasitism was recorded (Ritcher, 1966). The European earwig is believed to be less abundant than before the parasites were introduced, but nevertheless it is often a severe nuisance as a house and garden pest. This is indicated by a survey of the opinions of California structural pest control operators as to the relative importance of the 6 most important pests (termites excluded) that they have been called upon to control. These pests, in descending order of importance, were reported to be: in northern California, German cockroaches, ants, earwigs, mice, fleas, and silverfish; in central California, German cockroaches, earwigs, mice, silverfish, brownbanded cockroaches, and black widow spiders; and in southern California, German cockroaches, ants, fleas, oriental cockroaches, earwigs, and silverfish (PCOC, 1973). Earwigs were not listed as to species, but the European earwig was the principal pest species in most areas.
Description. This fully winged species is usually larger than the European earwig, ranging from 20 to 25 mm in length - usually slightly less than 25 mm. The color varies from pale brown, with distinct black markings, to chestnut or reddish brown, with the dark markings somewhat merged into the general color. The abdomen is usually banded, and the forceps vary from yellowish to reddish brown and are darker near the tips. The antennae and legs are yellowish. The last segment of the male's abdomen usually bears 2 short spines that are larger and more strongly developed on large specimens. The male's forceps are usually elongate and conspicuously toothed (figure 358, A), but some are shorter and weakly toothed (figure 358, B). The female's forceps (figure 358, C) are close together where they are, attached to the abdomen, and bear short, basal teeth along their inner margins, but these are sometimes hardly noticeable (A. B. Gurney, correspondence).
Life Cycle. Striped earwigs live in subterranean burrows beneath rubbish, mulches, and turf thatches. One female was observed to seal the entrance to a burrow she had made, after depositing 51 eggs within the burrow, tending them, washing them, and moving them about. (The eggs become covered with fungi or desiccated if a female is removed after ovipositing.) The eggs hatched in 7 days, and the first-instar nymphs fed on the egg cases. The nymphs remained in the burrow, and were groomed and manipulated.until their first molt, which occurred in another 7 days. The female then released them from the burrow and lost her maternal interests, devouring any nymphs she could capture. Depending on the amount of food (maggots) and water provided, the nymphs matured in from 49 to 60 days (average 56) at temperatures varying only a few degrees from 78 °F (26 °C) (Clements and Kerr, 1969). Labidura riparia was observed to lay 3 or 4 clutches of eggs per year in Europe (Caussanel, 1970).
Habits. Apparently, all North American species of earwigs are predatory, but. they are also scavengers. Striped earwigs seem to eat any food they encounter, such as garbage, cat and dog foods, or insect carcasses. They are not known to damage plants as the European earwigs do. Most of the earwigs (96.5%) found around structures in Florida in 1967 were Labidura riparia, the remainder being principally the ringlegged earwig, Euborellia annulipes, and a few spinetailed earwigs, Doru aculeatum (Scudder). However, during part of the summer of 1968, D. aculeatum was one of the most common earwigs, when large numbers developed and flew to lights (Clements and Kerr, 1969). Labidura riparia was trapped in flight (toward lights) only on nights after rainfall had occurred the previous day or night. The initial flight coincided with the maturation of the first generation of earwigs (Gross and Spink, 1971).
Economic Importance. In the Gulf states and California, striped earwigs became important household pests during the 1960's. They appeared to be attracted to lights and/or to other insects that were also attracted to lights. Their disagreeable odor, intensified if they are crushed, resulted in this species being particularly detested. Infestations in a residence could usually be detected, because of the characteristic odor, before the insects were seen. Another noteworthy peculiarity of these insects was their inherent resistance to chlorinated hydrocarbons. As a result, the application of 10% granular heptachlor to urban yard and field test plots, which eliminated important predators (imported fire ant and thief ant), greatly increased the striped earwig population (Gross and Spink, 1969).
Description. The ringlegged earwig is 12 to 15 mm long, wingless, and dark brown to black, with a yellowish-brown undersurface. The legs are yellowish, with femora, and tibiae bearing fuscous rings. The black, 16-segmented antennae have the third, and usually the fourth, segment from the apex white. The female has 8 abdominal tergites, and the male has 10. Typical forceps of male and female are shown in figure 358, D and E, respectively. The nymphs resemble the adults. In the successive nymphal instars, the number of antennal segments is 8 in the first, 11 in the second, 13 in the third, 14 in the fourth, and 16 in the fifth (Bharadwaj, 1966).
Life Cycle. Females can produce as many as 6 clutches of eggs from a single mating (Klostermeyer, 1942), but usually produce 1 to 4 (Bharadwaj, 1966). The eggs average 0.845 mm long, and are at first creamy white and ovate, but later become gray or brownish and kidneyshaped. The average number of eggs laid per female has been recorded as 47 (Klostermeyer, 1942), and as 52.7 (Bharadwaj, 1966). Klostermeyer found the preoviposition period to be an average of 10.8 days; egg stage, 14.3 days; and nymphal stage (5 instars), 80.7 days. Some females lived as long as 7 months after reaching maturity. Females outnumbered males by a ratio of about 4 to 1.
Economic Importance. The ringlegged earwig has been recorded as a pest of Irish and sweet potatoes in storage, in flour mills, breweries, meatpacking plants, and slaughterhouses, damaging the roots of vegetables grown in greenhouses, and as a pest in gardens and nurseries. It was reported as one of the principal pests in corn-processing plants (Gould, 1948). It acts as a carrier of certain endoparasites of fowls in Hawaii. It has become a nuisance by invading houses, particularly in the Gulf states. On the other hand, it is of some value as a predator on certain insect pests, including leafhoppers, beetles, moths, and various stored grain pests (Klostermeyer, 1942; Bharadwaj, 1966).
Description. These earwigs are black, with a reddish tinge. Their legs are yellow or amber, usually with faint, smoky markings on the femora and tibiae. Mature specimens average 14 mm in length. Some adults are wingless, or have short wings and are easily confused with Euburellia annulipes, which is always wingless (in California) and is similar in general appearance. However, normally in both sexes of E. cincticollis, antennal segments 15 and 16 are white, the remainder being dark brown, whereas in E. annulipes, usually segments 12 and 13 are white. An occasional specimen of either species will have antennae with all segments dark. Specimens of E. cincticollis have only faint, smoky areas on the femora and tibiae, whereas the legs of E. annulipes are prominently black-spotted (Ting, 1951). A distribution map shows E. cincticollis to be limited to interior localities of California, whereas E. annulipes occurs both inland and along the coast (Knabke and Grigarick, 1971).
Euborellia cincticollis, as well as E. annulipes, can be distinguished from the European earwig, Forficula auricularia, in that the latter lacks the white antennal segments, and the forceps also differ greatly in size and shape, being larger and more "forcepslike" in the male (Ting, 1951). Also, in F. auricularia the second tarsal segment is lobed, whereas in the genus Euborellia it is cylindrical (Knabke and Grigarick, 1971).
Life Cycle. The African earwig normally remains almost entirely hidden in the soil at depths of about 2 to 30 cm, or under vegetative growth. Eggs are laid from late April to July and August. Field-collected females produced and brooded several clutches of eggs in the laboratory at 2 to 4 week intervals, averaging a total of 83.7 eggs per female. The average periods from egg to adult were 128 days at 22 to 27 °C, 78 days at 27 to 29 °, and 82 days at 32 to 331. Five nymphal instars were most common at 22 to 27 ° and 6 to 7 instars were most common at 32 to 33 °. One or 2 generations per year were estimated to be produced in the field. Both nymphs and adults were noted to overwinter. Field-collected adults survived as long as 240 days in the laboratory, and were believed to be able to live a year or more in the field. In one investigation, flights of E. cincticollis occurred between July 14 and September 26, but major flights did not occur until August 12. Flights took place mainly from sunset to about 10 p.m. (Knabke and Grigarick, 1971).
Although the European and ringlegged earwigs are susceptible to organochlorine insecticides, the striped earwig is not. It can be controlled with organophosphorus or carbamate insecticides, such as malathion, diazinon, and carbaryl. Propoxur was found to be a particularly toxic insecticide for Labidura riparia. The LC50 for propoxur was 0.04% compared with 0.13% for diazinon. However, treatments applied inside the house, as for cockroaches, did not control striped earwigs. They could be controlled by applying insecticide to the soil in areas 1 to 2 yd (1 to 2 m) wide around the perimeters of structures. Propoxur bait performed well in tests, but would probably have to be applied once a month (Clements and Kerr, 1969).
Crickets and katydids both have long, filiform antennae. The tegmina of crickets lie flat on the back, but are bent down abruptly on the sides, and the tarsi are 3-segmented. The tegmina of katydids are held rooflike over the back, and the tarsi are 4-segmented.
Of the 2 groups, the occasional household pests are the crickets. Two species may be involved the field cricket, "Gryllus assimilis" (quotation marks are explained in the following text), and the house cricket, Acheta domesticus. In the western states, the field cricket is the principal pest. When their natural food supply of grasses dries up, crickets may migrate, and homes and other buildings may be invaded by thousands of these insects.
Multitudes can be attracted to lights and will sometimes cover streets and walks several inches deep (see under "Economic Importance"). They usually enter a building during the first cold days in the fall, through cracks and apertures such as around poorly fitted doors or loose basement windows. Some are carried in with firewood. Excessive rainfall may cause household or other building invasion.
Description. In the United States, field crickets range in length from 13 to 28 mm, and from solid black to pale straw color. They have long, slender antennae, much longer than the body. The females have 3 conspicuous appendages extending from the tip of the abdomen, the middle one being the ovipositor (figure 359). The males may be distinguished by their having only 2 caudal appendages. Alexander (1957) recognized that, among field crickets, forms that were morphologically similar in different localities could be found in 3 types of habitats: "(1) large, light-colored forms in sandy areas (beaches, sand dunes, and deserts); (2) small, black forms in deciduous forests; and (3) forms intermediate between these two extremes in grassy and weedy areas, such as prairies, fields, pastures, roadsides, and lawns."
Life Cycle. Severin (1926) gave an account of the life cycle of "Gryllus assimilis" based on 12 years of investigation of the insect in South Dakota. He believed that there were 2 biological races in that state, one of which, probably less than 5% of the cricket population, overwinters as nymphs of usually the fifth and sixth instars, under leaves, trash, and other debris. They become adults during the latter part of May, reproduce during June, and die in July. The other race overwinters in the ground in the egg stage. They reach maturity during late July and early August. Many live out their life span, reproduce, and die by mid-September, but some live until they are destroyed by a heavy freeze. There is very little overlapping of living adults of the 2 races.
In the race that hibernates in the egg stage females begin to oviposit within 2 weeks after becoming adults, and continue until they die. They prefer to oviposit in soil that is firm, but soft enough to permit the ovipositor to enter readily. They prefer damp soil, such as that along ditches or at the bases of cracks in baked soil, or they will uncover damp soil by digging pits with the first 2 pairs of legs (Metcalf et al., 1962). The eggs are deposited 7 to 25 mm beneath the surface. They are laid singly, but 50 or more may be laid in an area about 5 cm square. A female normally lays 150 to 400 eggs. When first laid, they are light honey-yellow, and 2.8 to 3.2 mm long. After passing through the winter, they are cream-colored and slightly larger (Severin, 1926). According to Severin, field crickets passed through 8 or 9 instars. There was little difference in the period required by males and females for nymphal development, and it ranged from 82 to 93 days. In the Gulf states and the California deserts, "Gryllus assimilis" overwinters in nymphal instars, and is active throughout the year. There may be as many as 3 generations per year.
Economic Importance. The field cricket can destroy field crops such as alfalfa, alfalfa seed, cereals, and vegetable crops such as tomatoes, cucumbers, peas, beans, and strawberries. Great outbreaks of field crickets occasionally occur in several states simultaneously in the Midwest and South (Howell and Hensley, 1953; Hutchins and Langston, 1953). They sometimes invade towns and cities in great swarms. At such times, the sides of buildings may be covered with the insects, and it is necessary to sweep them from store fronts and sidewalks. They can become so abundant on streets and sidewalks under street lights that the slipperiness resulting from crushed crickets causes driving and walking to be hazardous. During such invasions of populated areas, the crickets, will also invade houses and other buildings. They have been reported to damage articles made of nylon, wool, plastic fabrics, and leather (Howell and Hensley, 1953), and "to eat holes in paper and rubber and in cotton, linen, woolen, or fur garments, either outdoors or indoors, especially when soiled with perspiration or foods" (Metcalf et al., 1962). The odor of dead crickets may be unbearable if they are not removed. During these invasions, cats may reject food and eat only crickets. The cats become emaciated and are subject to fits (R. N. Hawthorne, correspondence). Fortunately, field crickets cannot adapt themselves like house crickets to conditions within houses, and will die off by early winter (NPCA, 1968).
Folsom and Woke (1939) believed that during summers of extended drought, field crickets developed in large numbers when soils cracked extensively and provided shelter for the insects against weather and predators. Howell and Hensley (1953) observed that great swarms of crickets that invaded cities and towns were usually correlated with severe drought, followed by rainfall sufficient to produce food adequate for cricket development. However, in the desert valleys of southeastern California, where summer thunderstorms occasionally occur on days of especially high temperature, great swarms of crickets will invade towns on the same day as a thunderstorm takes place. This happens nearly every summer. Five mm of rain can trigger such an outbreak.
Description. The adult averages about 20 mm long, and is light yellowish brown or strawcolored, with 3 dark bands on the head (figure 360). As with the field cricket, it has slender antennae that are longer than the body.
Life Cycle. Under laboratory conditions, the female lays an average of 728 eggs at 28° C (82° F), and there are 7 to 8 nymphal instars. The nymphal stage (over-all) requires, on the average, 55.8 days for males and 52.9 days for females. The preoviposition period averages 10 days, oviposition period 35 days, and postoviposition period 19 days (Ghouri and McFarlane, 1958). In the field, overwintering eggs generally hatch in late spring, and the adults appear in late summer, there being only 1 generation per year.
Economic Importance. During a 15-year period of investigation before 1935, the house cricket was more often encountered outdoors than indoors (Back, 1936). Wherever it had become a serious household pest in 35 cities and towns, the infested houses were located near an active city trash dump. In these dumps, the crickets were not seen during the day unless they were exposed by removing objects under which they were hiding. With the approach of darkness, they began to migrate, crawling or flying, particularly after city lights were turned on. They then appeared in large numbers on tree trunks, telephone or electric light poles, and on the sides of houses, sometimes entering second and third-story windows or skylights on the roof. During such infestations, one could scarcely move an article of furniture or other object in a house without uncovering crickets. Infestations tended to continue until the trash dumps or fills were covered over with earth.
In infestations such as those just described, all types of clothing are damaged. Large areas are eaten out of the fabric, rather than the small holes typical of clothes moth infestation. Heavy damage to wool, cotton, silk, synthetic fabrics, and even carpeting has often been reported (Back, 1936). Clothes stained with perspiration are particularly attractive to crickets.
In a controlled experiment with cotton and synthetic fabrics, house crickets caused severe damage to some synthetic fabrics and some damage to all of them. There was, greater damage to clean fabrics than to the same fabrics when stained with an animal fat collected from kitchen food preparation drippings and strained through an 80-mesh screen. Damage to the unstained acetate, viscose, and triacetate fabrics was extensive. There was slight damage to the polyester, nylon, and acrylic fabrics. Crickets preferred the same 3 fabrics as American cockroaches with which they were compared. There apparently was no damage to cotton fabrics (Finley et al., 1968).
Mallis (1969) quoted D. E. Howell as stating that in 1954, a field cricket infestation in Stillwater, Oklahoma, was controlled with a 0.5% lindane spray. Four hours later, more than 75 cu m of crickets were swept up in the downtown areas of the city. In later tests, malathion, diazinon, and other organophosphorus insecticides were found to be even more effective than lindane.
Removal of ivy and shrubs from buildings is said to aid in cricket control. Openings in buildings, particularly at the thresholds of doorways, should be sealed. Residual sprays applied to baseboards, in closets, under stairways, and around fireplaces are said to be useful, keeping in mind that field crickets are usually restricted to basements and ground-floor levels, whereas house crickets may be found in any part of the house. Any insecticides and concentrations used for cockroaches are effective in cricket control. Insecticide dusts, such as Dri-die 67®, Drione®, 5% chlordane, or sodium fluoride are useful in enclosed spaces, such as attics, crawl spaces, wall voids, or behind baseboards. Kepone® pellets may be applied under drawers, sinks, and in other hiding places, as in cockroach control. Following a residual spray, a space spray or aerosol may be useful to drive many of the crickets out of hiding places and cause them to contact fresh residual deposits. In the southern states and the desert valleys of the Southwest, it is necessary to treat outdoors as well as in buildings. Some infestations of house crickets have been controlled by covering the city dump with earth.
Habits. Although mole crickets spend most of their time in permanent burrows several inches deep in the soil, they may come to the surface when the soil has become wet, and particularly at night when temperatures are above 70 °F (21 °C). They will then make temporary burrows in the upper stratum (2.5 or 5 cm) of the soil, and can cause serious damage to lawns and golf courses by their burrowing. They are among the major pests of turf in Florida and some other southeastern states. They also crawl about on the surface and feed on ripening strawberries and the fruits of other crops if they touch the ground. They occasionally enter basements of buildings (Wisecup and Hayslip, 1943; Short, 1973).
Crampton (1923) observed a species of Ceuthophilus crawling about in the open privies in a mountain camp in Massachusetts and the same species crawling over food on pantry shelves. He was surprised to find no reference to these insects as vectors of pathogenic organisms.
At Los Angeles, we receive many telephone calls concerning this strange-looking creature, despite its relative scarcity. It is one of the few insects that the layman adequately describes. Common questions are, "Is it dangerous?" and "What shall I feed it?" The Jerusalem cricket is harmless, although when cornered it may rise on its hind legs, facing the annoyer, and jump at the attacker if teased sufficiently. Its powerful mandibles can inflict a minor, nonvenomous wound when it is handled carelessly. It may also make a sound like 2 pieces of sandpaper rubbed together by scraping the hind legs against the tough plates on the sides of the abdomen. These insects are becoming more prevalent in California, and are entering houses in increasing numbers, if one may judge by the inquiries received from homeowners. They have even been found in third-floor apartments.
Description. Stenopelmatus fuscus (figure 362) is the largest member of the genus, being 30 to 50 mm long; an occasional specimen may be larger. The head, thorax, and legs are shining, pale amber-yellow to brownish. There is not the slightest vestige of wings. Dorsally, the abdomen is shining amber-brown, with wide, almost black, bands across the anterior margins of the segments, and ventrally it is pale amber. The long hind tibiae have 2 or 3 outer and 4 or 5 inner spines. The male has a more massive head and thorax and a smaller abdomen than the female.
Biology and Habits. Jerusalem crickets are nocturnal and are not often seen, but in winter, spring, and early summer they may be found under rocks in open, grassy pasture land, or may occasionally be seen crawling about in the evening. Baker (1971) described the interesting trail left by one of these insects in soft dirt: "A snakelike, continuous track made by the dragged abdomen, with a series of cleatlike tracks on either side, made by the legs. By following these tracks on a warm evening, one may sometimes find the insect searching for food." In California, they estivate in the fall, and can then be obtained only by digging in manure heaps and damp places. In captivity, they will eat bread, grass roots, vegetables, and fruit, but prefer any kind of meat or small insects. After copulation, the females may kill and eat the males.
The Jerusalem cricket burrows in the soil, but unlike the mole cricket, which burrows with specialized fore tibiae, the Stenopelmatus does its digging mainly with its large and heavily sclerotized head. The closed mandibles are used as a hoe, scraping the earth back and underneath. In southern California, they have been found in moist, light, loamy soil or in deep cracks in adobe soil. The females make nest burrows beneath rocks or boards that extend downward for 6 to 1 0 in. (15 to 25 cm), then turn sharply to one side and end in an enlarged chamber, often lined with a paperlike substance, in which the eggs are laid. The eggs. are whitish, oval, and about 3 mm in diameter (Davis, 1927; Baker, 1971).
Description. The adults of Leptocoris trivittatus average about 12 mm long, are rather flat and narrow, gray-brown to black, and have red margins on the basal halves of the wings. The adults of L. rubrolineatus are a little shorter and narrower than those of L. trivittatus. They average about 10 mm long, and the basal halves of the wings have not only red margins, but also 3 longitudinal red stripes (plate VIII, 8). The nymphs are bright red at first, but become marked with black when about half grown.
Biology. In the spring, the overwintering females lay their minute, red eggs in cracks and crevices of the bark of the host plant. The eggs hatch in about 2 weeks, close to the time when the new leaves are about to appear. There are 5 nymphal instars.
In the warmer regions of the United States, there are 2 generations per year. In California, all stages mass-migrate periodically, covering the ground, shrubs, and fences. What motivates the bugs to migrate is not known.
Chemical control can best be obtained by spraying the nymphs on the host trees before the adults have had a chance to migrate. Power spray equipment is usually required. Many residual insecticides have been successfully used. Malathion is suggested for those interested in an insecticide of minimal mammalian toxicity and with a brief residual life. One spray on the ground, tree trunks, and fences will usually control the pests, despite the brief residual life of malathion (R. N. Hawthorne, correspondence). In the home, the insects can be collected with a tank-type vacuum cleaner and then destroyed. Good control has also been obtained by applying aerosols containing TDE plus synergized pyrethrins. Before the advent of organochlorine insecticides, ordinary pyrethrin fly sprays were recommended for indoor treatment of boxelder bugs (Craighead, 1950). When referring to conditions in the eastern United States, Vasvary (1965) suggested, for indoor infestations 2% chlordane in deodorized kerosene, sprayed or painted into cracks and on surfaces where boxelder bugs were hiding, paying particular attention to attics, especially close to the eaves, and to the cellars near foundation walls.
Nomius pygmaeus (Dejean), the stink beetle, occasionally invades houses in the western states. It has a particularly offensive odor that is retained for weeks on household articles upon which the beetle has crawled (Hinton, 1945). Its presence in towns has been associated with near-by forest fires, the insects apparently having been driven out of the forests by smoke (Spencer, 1942). The control measure just suggested for the tule beetle should also be effective against other carabids that have similar habits.
The Egyptian alfalfa weevil (figure 366-67, C) resembles the more widely distributed alfalfa weevil, H. postica (Gyllenhal), in appearance, life history, and habits. The adult is about 5 mm long, grayish brown to nearly black, with short, grayish hairs. It belongs in a subfamily (Curculi-oninae) in which the beak is long and slender. In H. brunneipennis, the beak projects downward from the front of the head and is about half the length of the thorax. The adults hibernate about the crowns of alfalfa (or clover) plants or under leaves and rubbish, then feed a few days and mate. The females lay as many as 40 oval, yellowish eggs in cavities they make with their beaks in alfalfa stems, and may lay from 400 to 600 eggs each during the spring. The green larvae, with a prominent dorsal stripe, feed on alfalfa and become mature about the time the first crop is cut. They then spin a netlike, nearly spherical, cocoon in the ground and pupate, emerging as adults in about 10 days. The adults also feed on alfalfa plants, and may occur in enormous numbers.
The weevils tend to migrate from alfalfa fields to marginal areas, tree rows, fence rows, buildings, and sheltered locations, and sometimes invade residences. Entomologists of the California Department of Agriculture became aware of over 30 invasions of houses by alfalfa weevils in a single month (November, 1971) from specimens sent to their taxonomists by agricultural commissioners from all areas of the state. Probably many other such invasions were not reported. The beetles cause no spotting problem such as caused by weed bugs, and leave no disagreeable odor as do the weed bugs and tule beetles, but nevertheless they are pests merely because of their unwanted presence in the home.
Destruction of wild strawberries in the vicinity of houses helps to control both these species. Also, thorough spraying of foundations with wettable powders of chlordane or lindane, or applying them as dusts, has proved to be useful in control. The surrounding area within 10 ft (3 m) of the foundation should also be treated. The treatments may need to be repeated in about 3 weeks and possibly again later. If the beetles invade the home, gathering them up with a vacuum cleaner seems to be the best procedure (Cress, 1971).
In the areas containing the crypts, some kinds of mycetophilids feed on the fungi at imperfect seals on the outsides of the concrete shutters while the crypts are damp inside. (See the detailed discussion of fungus gnats in chapter 10.) Certain common species of beetles may sometimes be seen in the hallways.
The insect species that were collected during the foregoing investigations were as follows:
Fig. 352. European brown snail, Helix aspersa.
Fig. 353. Snail eggs in a nest in damp soil. (From Basinger, 1931.)
Fig. 354. An amphipod, Tatitroides sylvaticus, that sometimes invades houses.
Fig. 355. Clover mite, Bryobia praetiosa.
Fig. 356. European earwig, Forficula auricularia. Female (left); short-forceps-type male; long-forceps-type male.
Fig. 357. European earwig, Forficula auricularia, and newly hatched nymphs in subterranean nest. An example of maternal care for the young among insects. (From Fulton, 1924a)
Fig. 358. Forceps of 3 species of earwigs. A, Labidura riparia (male, large type); B, Labidura riparia (male, small type); C, Labidura riparia (female); D, Euborellia annulipes (male); E, Euborellia annulipes (female); F, Forficula auricularia (male, short type); G, Forficula auricularia (female); H, F. auricularia (male, long type).
Fig. 359. Field cricket, "Gryllus assimilis."
Fig. 360. House cricket, Acheta domesticus.
Fig. 361. Two California camel crickets. Top, Ceuthophilus californianus; bottom, Pristoceuthophilus pacificus (adult male).
Fig. 362. Jerusalem cricket, Stenopelmatus fuscus
Fig. 363. Weed bug, Arhyssus crassus.
Fig. 364. Grass bug, Nysius raphanus.
Fig. 365. Darkling ground beetle, Coniontis subpubescens.
Fig. 366-67. Some crop pests that can invade the home. A, black vine weevil, Brachyrhinus sulcatus; B, cribrate .weevil, Brachyrhinus cribricollis, C, Egyptian alfalfa weevil, Hypera brunneipennis.
Fig. 368. Greater wax moth, Galleria mellonella, adult and larva.
Fig. 369. A stratiomyid fly, Hermetia illucens, adult and larva.
Fig. 370. Applying lindane vapor through a vent pipe of a mausoleum with a vapor generator.