Dermaptera

(Earwigs)

Class Insecta

Order Dermaptera

Number of families 28

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 Forficulina,

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.

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 tropical Africa and Arixeniina live on bats in the Malayan-Philippine 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.

Reproductive biology

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

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.

Species accounts

List of Species

No common name

Arixenia esau

family

Arixeniidae

taxonomy

Arixenia esau Jordan, 1909.

other common names

None known.

physical characteristics

Robust, hairy, apterous, and almost blind, with long legs and rodlike cerci.

distribution

Malaysia, Indonesia, and the Philippines.

habitat

On the naked bat Cheiromeles torquatus (Molossidae) and its roosts.

behavior

Obligatory associated with host; in other words, unable to survive away from the naked bat.

feeding ecology and diet

Skin-gland secretions of their hosts and occasionally dead insects.

reproductive biology

Viviparous.

conservation status

The host bat Cheiromeles torquatus is listed as Lower Risk/Near Threatened by the IUCN; maintenance of adequate populations of the host bat are necessary to preserve this earwig.

significance to humans

The world's first earwig reserve was created in Niah Great Cave, Sarawak, to protect this rare species.

European earwig

Forficula auricularia

family

Forficulidae

taxonomy

Forficula auricularia Linnaeus, 1758, Europe.

other common names

English: Common earwig; French: Perce-oreilles; German: Gemeiner Ohrwurm; Spanish: Tijereta europea; Italian: Forficola.

physical characteristics

Reddish-brown. Tegmina and legs are yellow brown. Adults are winged, with a length of 0.47–0.59 in (12–15 mm). Male forceps are broadened and crenulated basally and 0.16–0.31 in (4–8 mm) long. Female forceps is 0.12 in (3 mm). Larvae look like adults but are wingless and smaller.

distribution

Originally known from the Palearctic region (Europe, western Asia, and North Africa), the European earwig has been introduced into East Africa, North America, the East Indies, Australia, New Zealand, Chile, and Argentina.

habitat

It hides among petals or leaves of garden plants or inside fruit, shrubbery, fences, woodpiles, bases of trees, and behind loose boards on buildings.

behavior

Nocturnal, hiding during the day and roaming at night to find food and water.

feeding ecology and diet

Polyphagous, feeding on plants, ripe fruit, lichens, fungi, and other insects.

reproductive biology

Clusters of 50–90 eggs are laid in chambers in moist soil from November to January; a second batch containing fewer eggs is deposited in March or April. Egg development takes from 10 to 90 days, depending on the temperature. The larval stage lasts 40–50 days, including four instars. Females guard the eggs and first instar larvae, excluding males from the nest. Univoltine (having one generation per year); all stages are present except in autumn, when there are only adults.

conservation status

Not listed by the IUCN.

significance to humans

Not considered of great economic importance in Europe, but a serious pest in parts of the United States on flower crops, butterfly bush, hollyhock, lettuce, strawberry, celery, potatoes, sweet corn, roses, seedling beans and beets, and tender grass shoots and roots. They are sometimes beneficial, feeding on pests such as aphids, even on the above-mentioned crops.

St. Helena earwig

Labidura herculeana

family

Labiduridae

taxonomy

Labidura herculeana Fabricius, 1798; St. Helena.

other common names

None known.

physical characteristics

Largest earwig, with a body length of 1.44–21.6 in (36–54 mm) and forceps of 0.6–0.96 in (15–24 mm), reaching up to 31.2 in (78 mm). Females are shorter than males. Black body, reddish legs, short tegmina, and no hind wings.

distribution

Horse Point Plain in the extreme northeast of the mid-Atlantic island of St. Helena.

habitat

Dry and barren, with stony soil, bushes, and tufts of grass.

behavior

Living specimens have been found under stones or near burrows in the soil. They are nocturnal and active during summer rains.

feeding ecology and diet

Nothing is known.

reproductive biology

Mating takes place between December and February, and females with eggs have been seen in March.

conservation status

Rediscovered in 1965 for the first time since the original description. Dead remains seem to indicate a shrinking range, due to unknown causes. No living specimens have been found recently, and the species could be extinct. Study is needed to assess the status of the species. If it is extant, a detailed study on its ecology is necessary to design an appropriate protection and management program.

significance to humans

This species is of scientific interest because it is the largest earwig in the world.

Resources

Books

Carpenter, F. M. "Superclass Hexapoda." In Treatise on Invertebrate Paleontology, Part R Arthropoda 4, edited by R. L. Kaesler. Boulder, CO: Geological Society of America, 1992.

Chopard, L. "Ordre de Dermaptères." In Traite de Zoologie. Vol. 9, edited by P. P. Grassé. Paris: Masson and Cie, 1949.

Rentz, D. C. F., and D. K. M. Kevan. "Dermaptera." In The Insects of Australia (CSIRO), edited by D. F. Waterhouse, P.B. Carne, and I. D. Naumann. Ithaca, NY: Cornell University Press, 1991.

Sakai, S. Dermapterorum Catalogus Praeliminaris. 4 parts. Tokyo: Department of Biology and Chemistry, Daito Bunka University, 1970–1973.

Sakai, S. "A New Proposed Classification of the Dermaptera with Special Reference to the Check List of the Dermaptera of the World." Addition and Errata. Dermapterorum Catalogus 14 (1982): 1–108.

Periodicals

Giles, E. T. "The Comparative External Morphology and Affinities of the Dermaptera." Transactions of the Royal Entomological Society of London 115 (1963): 95–164.

Haas, F. "The Phylogeny of the Forficulina, a Suborder of the Dermaptera." Systematic Entomology 20 (1995): 85–98.

Natalia von Ellenrieder, PhD