Earwig

Earwigs make up the insect order Dermaptera, found throughout the Americas, Eurasia, Australia and New Zealand. With 1,800 species in 12 families, they are one of the smaller insect orders. Earwigs have characteristic cerci, a pair of forceps pincers on their abdomen, and membranous wings folded underneath short forewings, hence the scientific order name, "skin wings." Some groups are tiny parasites on mammals and lack the typical pincers. Earwigs rarely use their flying ability.

Earwigs are nocturnal; they often hide in small, moist crevices during the day, and are active at night, feeding on a wide variety of insects and plants. Damage to foliage, flowers, and various crops is commonly blamed on earwigs, especially the common earwig Forficula auricularia.

Earwigs have five molts in the year before they become adults. Many earwig species display maternal care, which is uncommon among insects. Female earwigs may care for their eggs, and even after they have hatched as nymphs will continue to watch over offspring until their second molt. As the nymphs molt, sexual dimorphism such as differences in pincer shapes begins to show.

Some earwig specimen fossils are in the extinct suborder Archidermaptera dating to the Late Triassic. Many orders of insect have been theorized to be closely related to earwigs, though Grylloblattaria is the most likely.

Etymology

The scientific name for the order, Dermaptera, is Greek in origin, stemming from the words dermatos, meaning skin, and pteron, wing. It was coined by Charles De Geer in 1773. The common term, earwig, is derived from the Old English , which means "ear", and , which means "insect". The name may be related to the old wives' tale that earwigs burrowed into the brains of humans through the ear and laid their eggs there. Earwigs are predisposed to hiding in warm humid crevices and may indeed occasionally crawl into the human ear canal (much like any other small organism).

is in turn related to wiggle, and ultimately to other words implying movement, including way and vehicle, all from PIE wegh-. English uses "to earwig" as a slang verb, to earwig meaning either "to attempt to influence by persistent confidential argument or talk". or "to eavesdrop".

Distribution

Earwigs are abundant and can be found throughout the Americas and Eurasia. The common earwig was introduced into North America in 1907 from Europe, but tend to be more common in the southern and southwestern states. found as far north as Canada, where it hides in the leaf axils of emerging plants in southern Ontario wetlands. However, other families can be found in North America, including Forficulidae (Doru and Forficula being found there), Labiidae, Anisolabididae, and Labiduridae.

Few earwigs survive winter outdoors in cold climates. They can be found in tight crevices in woodland, fields and gardens. Out of about 1,800 species, about 25 occur in North America, 45 in Europe (including 7 in Britain), and 60 in Australia. though some can grow longer, such as the Saint Helena earwig which reaches long. Earwigs are characterized by the cerci, or the pair of forceps-like pincers on their abdomen; male earwigs have curved pincers, while females have straight ones. These pincers are used to capture prey, defend themselves and fold their wings under the short tegmina.

The forewings are short oblong leathery plates used to cover the hindwings like the elytra of a beetle, rather than to fly. Most species have short and leather-like forewings with very thin hindwings, though species in the suborders Arixeniina and Hemimerina have no wings and are blind with filiform segmented cerci. The hindwing is a very thin membrane that expands like a fan, radiating from one point folded under the forewing. Even though most earwigs have wings and are capable of flight, they are rarely seen in flight. These wings are unique in venation and in the pattern of folding that requires the use of the cerci. The epizoic species, sometimes considered as ectoparasites, are wingless.

Internal

The neuroendocrine system is typical of insects. There is a brain, a subesophageal ganglion, three thoratic ganglia, and six abdominal ganglia; a ganglion being a mass of neurons. Strong neuron connects connect the neurohemal corpora cardiaca to the brain and frontal ganglion, where the closely related median corpus allatum produces Jeuvenile hormone III in close proximity to the neurohemal dorsal arota. The digestive system of earwigs is like all other insects: consisting of a fore-, mid-, and hindgut, albeit, earwigs lack gastric caecae which specialize in many species of insects for digestion. Long, slender (extratory) malpighian tubules can be found between the junction of the mid- and hind gut.

The reproductive system of females consist of paired ovaries, lateral oviducts, spermatheca, and a genital chamber. The lateral ducts are where the eggs leave the body, while the spermatheca is where sperm is stored. Unlike other insects, the gonopore, or genital opening is behind the seventh abdominal segment. The ovaries are primitive in that they are polytrophic; or the nurse cells and oocytes alternate along the length of the ovariole. In some species these long ovarioles branch off the lateral duct, while in others, short ovarioles appear around the duct. Each egg is approximately tall and wide.

The eggs hatch in seven days. The mother may assist the nymphs in hatching. When the nymphs hatch, they eat the egg casing and continue to live with the mother. The nymphs look similar to their parents, only smaller, and will nest under their mother and she will continue to protect them until their second molt in about July. The nymphs feed on food regurgitated by the mother, and on their own molts. If the mother dies before the nymphs are ready to leave, the nymphs may eat her.

After five to six instars, the nymphs will molt into adults. The male's forceps will become curved, while the females' remain straight. They will also develop their natural color, which can be anything from a light brown (as in the Tawny earwig) to a dark black (as in the Ringlegged earwig). In species of winged earwigs, the wings will start to develop at this time. The forewings of an earwig are sclerotized to serve as protection for the membranous hindwings.

Behavior

Most earwigs are nocturnal and inhabit small crevices, living in small amounts of debris, in various forms such as bark and fallen logs. Species have been found to be blind and living in caves, or cavernicolous; reported to be found on the island of Hawaii and in South Africa. Food typically consist of a wide array of living and dead plant and animal matter.

Ecology

Earwigs are mostly scavengers, but some are omnivorous or predatory.

feeding on flowers.]] The common earwig is one of the few insects that actively hunt for food and are omnivorous, eating arthropods, plants, and ripe fruit. To a large extent, this species is also a scavenger, feeding on decaying plant and animal matter if given the chance. Insects seen to have been caught include largely plant lice, but also large insects such as bluebottle flies.

Species of the suborders Arixeniina and Hemimerina are generally considered epizoic, or living on the outside of other animals, mainly mammals. In the Arixeniina, family Arixeniidae, species of the genus Arixenia are normally found deep in the skin folds and gular pouch of Malaysian hairless bulldog bats (Cheiromeles torquatus), apparently feeding on bats' body or glandular secretions. On the other hand, species in the genus Xenarina (still of the suborder Arixeniina) are believed to feed on the guano and possibly the guanophilous arthropods in the bat's nest, where it has been found. Hemimerina includes Araeomerus found in the nest of Long-tailed pouch rats (Beamys), and Hemimerus which are found on Giant Cricetomys rats.

Earwigs are generally nocturnal, and typically hide in small, dark, and often moist areas in the daytime. They can usually be seen on household walls and ceilings. Interaction with earwigs at this time results in a defensive free-fall to the ground followed by a scramble to a nearby cleft or crevice.

Predators and parasites

Earwigs are regularly preyed upon by birds, but like many other insect species are prey for insectivorous mammals, amphibians, lizards, centipedes and spiders. European naturalists have observed bats preying upon earwigs. Another tachinid fly and parasite of earwigs, Ocytata pallipes, has shown promise as a biological control agent as well. The common predatory wasp, the yellow jacket (Vespula maculifrons), preys upon earwigs when abundant. A small species of roundworm, Mermis nigrescens, is known to occasionally parasitize earwigs that have consumed roundworm eggs with plant matter. At least 26 species of parasitic fungus from the order Laboulbeniales have been found on earwigs. The eggs and nymphs are also cannibalized by other earwigs. A species of tyroglyphoid mite, Histiostoma polypori (Histiostomatidae, Astigmata), are observed on common earwigs, sometimes in great densities; however, this mite feeds on earwig cadavers and not its live earwig transportation. Hippolyte Lucas observed scarlet acarine mites on European earwigs.

Evolution

from the suborder Arixeniina]] from the suborder Hemimerina]] The fossil record of the Dermaptera starts in the Late Triassic to Early Jurassic period about in England and Australia, and comprises about 70 specimens in the extinct suborder Archidermaptera. Some of the traits believed by neontologists to belong to modern earwigs are not found in the earliest fossils, but adults had five-segmented tarsi (the final segment of the leg), well developed ovipositors, veined tegmina (forewings) and long segmented cerci; in fact the pincers would not have been curled or used as they are now. The theorized stem group of the Dermaptera are the Protelytroptera. These insects, which resemble modern Blattodea, or Cockroaches owing to shell-like forewings and the large, unequal anal fan, are known from the Permian of North America, Europe and Australia. There are no fossils from the Triassic when the morphological changes from Protelytroptera to Dermaptera took place. Species in Hemimerina were at one time in their own order, Diploglassata, Dermodermaptera, or Hemimerina. Like most other epizoic species, there is no fossil record, but they are probably no older than late Tertiary. that are attached to the frontal cuticle to the bases of the antennae. These features have not been found in other insects. An independent organ exists for each antenna, consisting of an ampulla, attached to the frontal cuticle medial to the antenna base and forming a thin-walled sac with a valved ostium on its ventral side. They pump blood by elastic connective tissue, rather than muscle.

Taxonomy

Distinguishing characteristics

The characteristics which distinguish the order Dermaptera from other insect orders are:

General body shape: Elongate; dorso-ventrally flattened.

Head: Prognathous. Antennae are segmented. Biting-type mouthparts. Ocelli absent. Compound eyes in most species, reduced or absent in some taxa.

Appendages: Two pairs of wings normally present. The forewings are modified into short smooth, veinless tegmina. Hindwings are membranous and semicircular with veins radiating outwards.

Abdomen: Cerci are unsegmented and resemble forceps. The ovipositor in females is reduced or absent.

The overwhelming majority of earwig species are in Forficulina, grouped into nine families of 180 genera,

Suborder Archidermaptera † :Protodiplatyidae

Suborder Arixeniina :Arixeniidae

Suborder Forficulina :Anisolabididae :Apachyidae :Chelisochidae :Diplatyidae :Forficulidae :Karschiellidae :Labiduridae :Labiidae :Pygidicranidae

Suborder Hemimerina :Hemimeridae

Relationship with people

Earwigs are fairly abundant and found in many areas of the world. There is no evidence that they transmit diseases to humans or other animals. Their pincers are commonly believed to be dangerous, but in reality even the curved pincers of males cause little harm to humans. It is a common urban legend that earwigs crawl into the human ear and lay eggs in the brain. Finding earwigs in the human ear is rare, as most species do not fly and prefer dark and damp areas (such as basements) rather than typical bedrooms.

References

External links

Dermaptera - Earwigs from CSIRO

Fact Sheet about Earwigs including information on habits and habitat

Bugs in the Ear urban legend from Snopes

Earwig Page from What's That Bug

Earwig Research Center by Fabian Haas, Heilbronn

BBC Science and Nature Wildfacts from BBC: Science & Nature

ringlegged earwig on the UF / IFAS Featured Creatures web site

Langston RL & JA Powell (1975) The earwigs of California (Order Dermaptera). Bulletin of the California Insect Survey. 20

Category:Orders of insects