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Dermaptera

(Earwigs)

Class Insecta

Order Dermaptera

Number of families 28

Photo: Earwigs are harmless to humans and do not, despite their name, enter the ear. (Photo by ©J. H. Robinson/Photo Researchers, Inc. Reproduced by permission.)

Evolution and systematics

The oldest-known fossils of Dermaptera comprise about 70 specimens from the Jurassic, about 208 million years ago. Earwigs are considered orthopteroid insects, closely related to Orthoptera and Phasmatodea, and they are divided into four suborders. Suborder Archidermaptera, represented by only 10 fossil species from the Jurassic, had segmented adult cerci and four to five segmented tarsi. Forficulina, with about 1,800 species in 180 genera, is the largest suborder. Adult cerci are unsegmented and forceps-like; larval cerci also are unsegmented, except in two primitive groups. Arixeniina comprise five species in two genera, and Hemimerina consist of 10 species in one genus; they are wingless and have filamentous cerci. According to some phylogenetic studies, Archidermaptera constitutes the sister group of the remaining suborders. No fossil Hemimerina and Arixeniina earwigs are known. Some authors consider Hemimerina to be a separate order.

Physical characteristics

Dermaptera are brown or black, sometimes with a light brown or yellow pattern; a few are metallic green. The head is prognathous with chewing mouthparts. The antennae are long, thin, and filiform; ocelli are lacking, and the compound eyes are well developed, except in the blind Hemimerina and almost blind Arixeniina. The thorax bears two pairs of wings, of which the first, called “tegmina,” is small and leathery, giving origin to the ordinal name (derma, meaning “skin,” and ptera, meaning “wings”). Tegmina are short, covering the top of only the first segments of the abdomen and leaving the posterior part of the abdomen exposed. Hemimerina, Arixeniina, and some Forficulina are secondarily wingless; in the remaining Forfi-

A female earwig (Forficula auricularia). (Photo by John Markham. Bruce Coleman, Inc. Reproduced by permission.)

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A female earwig brooding her young. (Photo by R. N. Mariscal. Bruce Coleman, Inc. Reproduced by permission.)

culina, the second pair of wings is membranous, large, almost semicircular, and complexly folded under the tegmina at rest. The abdomen is highly movable, with pair of unsegmented, usually pincer-like cerci at the posterior end (filamentous in Hemimerina and Arixeniina). Cerci usually are dimorphic: straight in females and curved or asymmetrical in males. Forficulina earwigs are elongate and slender, reaching 0.16–3.2 in (4–78 mm) in length (including the cerci). Hemimerina are about 0.4 in (10 mm) long, excluding cerci, and they have short, stout legs and a streamlined, smooth body for rapid movement through the fur of their hosts. Arixeniina have long and slender legs. Larvae of earwigs resemble adults except for the absence of wings; larvae of wingless species often are difficult to distinguish from adults. Larval cerci are simple and almost straight, and they resemble those of the female.

Distribution

Dermaptera are cosmopolitan (except polar regions), with the greatest diversity in the tropics and subtropics.

ical Africa and Arixeniina live on bats in the MalayanPhilippine region.

Behavior

Earwigs prefer to hide in dark crevices during the day and become active at night. Cerci are used to open the wings, for grooming, and for defense. Some earwigs have defensive glands on the second or third abdominal segment that release a foul-smelling liquid, and they can squirt this fluid up to 4 in (100 mm).

Feeding ecology and diet

Most earwigs are omnivorous, but there are some species that are predominantly herbivorous, predacious (on chinch bugs, mole crickets, mites, scales, aphids, and caterpillars), or scavengers. Hemimerina feed on scurf and fungi growing on the skin of giant rats. Arixeniina feed on the skin-gland secretions of bats and occasionally on dead insects.

Habitat

Forficulina earwigs frequent humid crevices of all kinds; they can be found under bark, between leaves, and under stones. Hemimerina live on the bodies of giant rats in trop-

Reproductive biology

Hemimerina and Arixeniina are viviparous, and Forficulina are generally oviparous. In temperate climates Forficulina

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adults overwinter in soil, and in spring females, sometimes assisted by males, build a brood chamber or nest in the ground, within rotting vegetation, or under a rock. After mating and laying eggs, females chase males out of the nest. Females tend their eggs, turning them around and licking them to prevent the growth of fungi until they hatch. Females then forage for food, which they feed to their young larvae. Larvae stay in the nest until the second or third instar, completing up to four or five instars in all. If larvae do not leave the burrow after one or two molts, mothers may eat them.

Conservation status

Of the more than 1,800 species of earwigs known, only one, the St. Helena earwig (Labidura herculeana) is on the IUCN Red List; it is categorized as Endangered.

Order: Dermaptera

Significance to humans

The name “earwig” derives from the mistaken belief that this insect enters the ear and bores into the brains of sleeping people. Thus their common name in different languages often refers to the ear (Danish, Dutch, English, French, German, Russian, and Swedish) or to the forceps (Italian, Finnish, Portuguese, and Spanish). Most earwigs have little or no economic importance. They may do some damage in gardens by feeding on ornamental plants, but they also may be beneficial by eating other insects. A few species, if abundant, may damage blossoms of ornamental plants by chewing the stamens or petals.

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1. Arixenia esau; 2. St. Helena earwig (Labidura herculeana); 3. European earwig (Forficula auricularia). (Illustration by Marguette Dongvillo)

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