Forfcula auricularia Linnaeus Dermaptera Forficulidae

Natural History

Distribution. European earwig was first observed in North America at Seattle, Washington in 1907. It spread quickly and was reported from Oregon in 1909, British Columbia in 1919, and California in 1923. It reached Rhode Island in 1911, New York in 1912, and most other provinces and northern states in the 1930s and 1940s. Now it occurs south to North Carolina, Arizona and southern California, but owing to its preference for temperate climates it is unlikely to become abundant in the southeastern states. It is not very tolerant of arid environments, but survives where irrigation is practiced. European earwig is native to Europe, western Asia, and northern Africa, but also has been introduced to Australia and New Zealand.

Other earwigs are abundant in North America, but few are as numerous as European earwig, and none are as damaging. The ringlegged earwig, Euborellia annulipes (Lucas) (discussed separately), and the African earwig, Euborellia cincticollis (Gerstaecker), are probably the only other species of concern to crop producers. Ringlegged earwig is widespread, but African earwig is limited to southwestern states. Neither species is native to North America.

Host Plants. This insect is omnivorous and feeds on a wide variety of plant and animal matter. Although its predatory habits somewhat offset its phytophagous behavior, on occasion European earwig can inflict significant injury to vegetables, fruit, and flowers. Bean, beet, cabbage, celery, chard, cauliflower, cucumber, lettuce, pea, potato, rhubarb, and tomato are among the vegetable crops sometimes injured. Seedlings and plants providing the earwigs with good shelter, such as the heads of cauliflower, the stem bases of chard, and the ears of corn, are particularly likely to be eaten, and also likely to be contaminated with fecal material. Among flowers most often injured are dahlia, carnation, pinks, sweet william, and zinnia. Ripe fruits such as apple, apricot, peach, plum, pear, and strawberry are sometimes reported to be damaged.

European earwig is reported to consume aphids, spiders, caterpillar pupae, leaf beetle eggs, scale insects, spiders, and springtails as well as vegetable matter. Aphid consumption is especially frequent and well-documented (McLeod and Chant, 1952; Madge and Buxton, 1976a,b; Mueller et al., 1988). In addition to the higher plants mentioned above, earwigs consume algae and fungi, and often consume vegetable and animal matter in equal proportions (Buxton and Madge, 1976a).

Natural Enemies. There are several known natural enemies, including some that were imported from Europe in an attempt to limit the destructive habits of this earwig in North America. Some authors have suggested that the most important natural enemy is the European parasitoid Bigonicheta spinipennis (Meigen) (Diptera: Tachinidae), which has been reported to parasitize 10-50% of the earwigs in British Columbia. Others, however, report low incidence of parasitism (Lamb and Wellington, 1975). Another fly, Ocytata pal-lipes (Fallen) (Diptera: Tachinidae), also was successfully established, but it causes little mortality. Under the cool, wet conditions of Oregon, Washington, and British Columbia, the fungi Erynia forficulae and Metar-hizium anisopliae also infect earwigs (Crumb et al., 1941; Ben-Ze'ev, 1986). The nematode Mermis nigrescens appears to be an important mortality factor in Ontario, where 10-63% of earwigs were infected during a two-year period (Wilson, 1971). However, this nematode has not been reported from earwigs elsewhere. Avian predation can be significant (Lamb, 1975).

Life Cycle and Description. One generation is completed annually, and overwintering occurs in the adult stage. In British Columbia, the eggs are deposited in late winter, hatch in May, and nymphs attain the adult stage in August. Overwintering females may also produce an additional brood; these eggs hatch in June and also mature by the end of August (Lamb and Wellington, 1975). In Washington, these events occur about one month earlier (Crumb et al., 1941). Only a single brood of eggs is produced in colder climates such as in Quebec (Tourneur and Gingras, 1992).

  1. The egg is pearly white and oval to elliptical. The egg measures 1.13 mm long and 0.85 mm wide when first deposited, but it absorbs water, swells, and nearly doubles in volume before hatching. The eggs are deposited in a cell in the soil, in a single cluster, usually within 5 cm of the surface. Mean number of eggs per cluster is reported to range from 30 to 60 eggs in the first cluster. The second cluster, if produced, contains only half as many eggs. Duration of the egg stage under winter field conditions in British Columbia averages 72.8 days (range 56-85 days). The second or spring brood of eggs requires only 20 days to hatch. They are attended by the female, who frequently moves the eggs around the cell, and apparently keeps mold from developing on the eggs (Buxton and Madge, 1974). Females guard their eggs from other earwigs and fight with any intruders.
  2. The nymphal stages, four in number, have the same general form as adults except that the wings increase in size with maturity. The cerci are present in all instars, growing in size with each molt. The body color darkens, gradually changing from grayish brown to dark brown, as the nymph matures. The legs are pale throughout. The wing pads are first evident in instar four. Mean head capsule width is 0.91,1.14,1.5, and 1.9 mm in instars 1-4, respectively. Mean body length is 4.2, 6.0, 9.0, and 9-11 mm, respectively. The number of antennal segments is 8, 10, 11, and 12 in instars 1-4. Mean duration (range) of instars under laboratory temperatures of 15-21°C is 12.0 (11-15), 10.2 (8-14), 11.2 (9-15), and 16.2 (14-19) days for instars 1-4. However, development time is considerably longer under field conditions, requiring 18-24, 14-21,15-20, and about 21 days for the corresponding instars. Young nymphs are guarded by the mother earwig, who remains in or near the cell where the eggs are deposited until the nymph's second instar is attained.
  3. The adult normally measures 13-14 mm long, exclusive of the pincher-like cerci (forceps), though some individuals are markedly smaller. The head measures about 2.2 mm wide. Adults, including the legs, are dark brown or reddish brown, though paler ventrally. The antennae have 14 segments. They bear a set of cerci at the tip of the abdomen. The pronounced cerci are the most distinctive feature of earwigs; in the male the cerci are strongly curved, whereas in the female they curve only slightly. They can use the cerci in defense, twisting the abdomen forward over the head or sideways to engage an enemy, often another earwig. Despite the appearance of being wingless, adults bear long hind wings folded beneath the abbreviated forewings. Although rearely observed to fly, when ready to take flight the adults usually climb and take off from an elevated object. The hind wings are opened and closed quickly, so it is difficult to observe the wings.

Earwigs are nocturnal, spending the day hidden under leaf debris, in cracks and crevices, and in other dark locations. Their night-time activity is influenced by weather. Stable temperature encourages activity, and it is favored by higher minimum temperatures but is discouraged by higher maximum temperatures. High relative humidity seems to suppress movement, whereas higher wind velocities and greater cloud cover encouraged earwig activity (Chant and McLeod, 1952). They produce an aggregation pheromone in their feces that is attractive to both sexes and to nymphs, and release quinones as defensive chemicals from abdominal glands (Walker et al., 1993).

Social behavior is weakly developed in European earwig. Males and females mate in late summer or autumn, and then construct a subterranean tunnel (nest) in which they overwinter. The female drives the male from the nest at the time of oviposition. Eggs are manipulated frequently, the female apparently cleaning them to prevent growth of fungi. She will relocate the eggs in an attempt to provide optimal temperature and humidity. Although the female normally keeps the eggs in a pile, as the time for hatching approaches she spreads the eggs in a single layer. After hatching, females continue to guard the nymphs and provide them with food. Food is provided by females carrying objects into the nest, and by regurgitation. Thus, there is parental care, but no cooperative brood care (Lamb, 1976).

The most comprehensive treatment of European earwig biology was provided by Crumb et al. (1941), though the publications by Jones (1917) and Fulton (1924) were informative. Lamb and Wellington (1974) described methods for rearing. Keys to western earwig species were provided by Langston and Powell (1975).

Dermaptera Forficulidae
Adult male European earwig.

Eastern species were considered by Hoffmann (1987). A synopsis of European earwig, including keys to related Canadian insects, was given by Vickery and Kevan (1985).

Damage

The economic status of earwigs is subject to dispute. Undoubtedly, earwigs sometimes damage vegetable and flower crops, both by leaf consumption and fruit injury. Foliage injury is usually done in the form of several small holes. Tender foliage may be completely devoured except for major veins. However, the physical presence of earwigs as crop contaminants is perhaps even more important, because most people find their presence and odor repulsive. The annoyance associated with their presence is exacerbated by the tendency of earwigs to aggregate, often in association with human habitations; most people simply find them annoying. Their propensity to consume other insects, particularly aphids, is an important element in offsetting their reputation as a crop pest. However, augmenting the earwig population by field release, and providing them with additional shelter to enhance survival, have had mixed success in suppressing aphid populations (Carroll and Hoyt, 1984; Carroll et al., 1985).

Management

  1. Population monitoring can be accomplished with baits and traps. Small piles of baits which can be checked during the evening, distributed in dense vegetation, often attract large numbers of earwigs. Wheat bran or oatmeal can serve as a bait. Traps take advantage of the natural tendency of earwigs to hide in crevices and dark spots, and can be used to detect presence of earwings and to estimate abundance.
  2. Residual foliar insecticides and baits containing toxicant can be used to suppress earwigs. Of numerous baits evaluated, Crumb et al. (1941) suggested that wheat bran flakes plus toxicant and a small amount of fish oil was optimal. Fulton (1924) believed fish oil unnecessary but suggested addition of glycerin and molasses. Commercial products are rarely formulated specifically for earwigs because they rarely are a severe problem. Rather, products sold for grasshoppers, cutworms, slugs, and sowbugs are applied for earwig control. Bait is most effective if applied in the evening.

Cultural Practices. On residential property or in small gardens, persistent trapping can be used to reduce earwig abundance, though this approach is not effective if the initial earwig density is high. Boards placed on the soil are attractive to earwigs seeking shelter. Even more earwigs accumulate if there are narrow grooves or channels in the board. Moistened, rolled-up newspaper placed in the garden in the evening and disposed of in the morning makes a convenient earwig trap for home gardens. A particularly effective collecting technique is to fill a flower pot with wood shavings and invert the pot over a short stake that has been driven into the soil. Traps can also be placed in trees because earwigs favor this habitat.

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