Earwig

Earwig Temporal range: Late Triassic to Recent
Common earwig, Forficula auricularia
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Hexapoda
Class:	Insecta
Order:	Dermaptera De Geer, 1773
Suborders
Archidermaptera Arixeniina Forficulina Hemimerina

Dermaptera is an order of insects, frequently called earwigs or pincerbugs based on a common misconception that they crawl into humans' ears and eat the brain. The order is relatively small among other insect orders, with only 1,800 recorded species in 12 families, found through out the Americas and Eurasia. Earwigs are characterized by cerci, or the pair of forceps-like pincers on their abdomen, and the membranous wings folded underneath short forewings, hence the literal translation of the order being "skin wings". Earwigs can fly, but are rarely seen doing so.

Earwigs are nocturnal; they often hide in small, moist crevices during the day, and are active at night, feeding on a wide variety of other insects and plants. Damage to various crops are commonly blamed on earwigs, especially the common earwig. But the harmfulness of earwigs to crops is still under debate, as they also eat certain insects that damage them.

Earwigs undergo an average of 5 molts over the course of a year, their average life expectancy, before they become adults. A unique behavior to the species is maternal care. Female earwigs are known to take extreme care of 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.

Earwig fossils have been found dating back 208 million years ago. Those specimens are now included in the extinct suborder Archidermaptera dating back to Late Triassic. The actual organization of earwig suborders is still debated, but in 1985, biologist E.J. Popham developed a chart describing the approximate relationships between the different taxa.

Etymology

The scientific name for the order, Dermaptera, is Greek in origin, stemming from the words dermatos, meaning skin, and pteron, or wing. It was coined by Charles De Geer in 1773. The far more common term, earwig, is derived from the Old English ēare, which means "ear", and wicga, which means "insect." The name comes from the old wives' tale that earwigs burrowed into the brains of humans through the ear and therein laid their eggs.

Wicga is in turn related to wiggle, and ultimately to other words implying movement, including way and vehicle, all from PIE *wegh-. Other languages have words based on the same premises: German Ohrenkneifer, Ohrwurm, or Ohrenhöhler; Dutch oorwormen or oorwurmen; French perce-oreille; Danish ørentviste; Slovak ucholak (ucho = ear, lak = scare); Romanian urechelniță; and Hungarian fülbemászó ("crawler-into-the-ear"). English has derived a verb from this, to earwig, meaning "to fill someone's mind with prejudice by insinuations" or "to attempt to influence by persistent confidential argument or talk". The German word Ohrwurm has the derived meaning of earworm. Hungarian also uses the phrase fülbemászó dallam, meaning "a catchy melody". Some dialects of Swedish have related names for the earwig, but standard Swedish, by contrast, uses the word tvestjärt, which translates as "two-tail", not unlike the Geordie forkytail.

Description

A diagram showing a male (left) and female (right) common earwig

Most earwigs are flattened (fit inside tight crevices) with an elongated body ranging from 5mm to 25mm. Though the Saint Helena earwig reaches 80 mm long. Earwigs are characterized by the cerci, or the pair of forceps-like pincers on their abdomen, though harmless; male earwigs have a curved pair of pincers, while females have straight pincers. The antanae are thread-like with at least 10 segments or more. 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.

Earwigs are mostly scavengers, but some are predatory or even omnivorous. The abdomen of the earwig is flexible and muscular. It is capable of maneuvering as well as opening and closing the forceps. The forceps are used for a variety of purposes. In some species, the forceps have been observed in use for holding prey, and in copulation. The forceps tend to be more curved in males than in females.

Behavior

An earwig from the Western Ghats

Earwigs are fairly abundant and can be found virtually everywhere, specially through out the Americas and Eurasia. The common earwig was introduced into North America in the 1907s from Europe and now occur through out North America, but tend to be more common in the southern and southwestern states. Few earwigs successfully survive winter outdoors in the northern states. They can be found in tight crevices in woodland, fields and gardens.

The common earwig is one of the few insects that actively hunt for food and are omnivorous, or eat other arthropods, plants, and ripe fruit. To a large extant, this species is also a scavenger, feeding on decaying plant and animal matter including garbage if given the chance. Insects that have been seen caught include largely plant lice and even large insects with its pincers, like bluebottle flies. Plants that they feed on typically include clover, dahlias, zinnias, butterfly bush, hollyhock, lettuce, cauliflower, strawberry, sunflowers, celery, peaches, plums, grapes, potatoes, roses, seedling beans and beets, and tender grass shoots and roots; they have also been known to eat corn silk, damaging the corn.

Earwigs are generally nocturnal, and typically spend the daytime hours hiding in small, dark, and often moist areas. They can usually be seen patrolling household walls and ceilings. Interaction with earwigs at this time results in a defensive free fall to the ground below, and the subsequent scramble to a nearby cleft or crevice. Earwigs are also drawn to damp conditions. During the summer, they can be found around sinks and in bathrooms. Earwigs tend to gather in shady cracks or openings or anywhere that they can remain concealed during daylight hours. Picnic tables, compost and waste bins, patios, lawn furniture, window frames, or anything with minute spaces (even artichoke blossoms) can potentially harbor them. Upon gaining entry to the basement and living areas of the home, earwigs can easily find cover in undisturbed magazine and newspaper piles, furniture/wickerwork, base boards, carpeted stairways, pet food dishes, and even inside DVD cases and keyboards. The only insect predator that preys on the earwig are parasitic species in tachinidae, or tachinid flies, whose larvae live like parasites in the earwig's body. The eggs and nymphs can also be cannibalized by other earwigs.

Life cycle and reproduction

The life cycle and developement of an earwig from egg to each instar

Earwig are hemimetabolous or undergo incomplete metamorphosis, meaning they develop in a series of molts, they undergo 4 to 6 instars, or molts. Adults live for about a year, starting from the egg. Females will start mating in the fall around September, the beginning of the mating season, and can be found together in the fall and winter. The male and female will live in a chamber in debris, crevices, or soil 2.5mm deep. After mating, the sperm may retain in the female for months before the eggs are fertilized. In late January or early March, the male will leave or be driven out by the female. After the female will begin to lay 20 to 80 pearly white eggs in 2 days. Some earwigs, those parasitic in the in the suborders Arixeniina and Hemimerina, are viviparous, or give birth to live young; they would be fed by a sort of placenta. When first laid, the eggs are white or cream-colored and oval-shaped, but right before hatching, they become kidney-shaped and brown. Each egg is approximately 1 mm (0.04 in) tall and 0.8 mm (0.03 in) wide.

A strange behavior has been observed among earwig species in maternal care. The mother will pay close attention to the needs of her eggs, though studies by entomologist have shown that the mother does not pay attention to the eggs as she collects them. The mother has been shown to pick up wax balls by accident, but would eventually be rejected as they must not have the proper scent. The mother will also vigorously defend the eggs from predators, not eating unless an egg goes bad, she will also continuously lick and clean the egg to protect it from fungus. The urge to will percist for days when the eggs, as seen in the studies, are removed; when the eggs were replaced after they hatched, the mother would continue with the urge to lick and them up to 3 months.

The mother may also assist the nymphs in hatching. After the nymphs hatch, they will eat their egg casings and continue to live with the mother. They 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 would have feed off their own mother's saliva and regurgitated vegetation, and also on their own molts. Another strange behavior observed is if the mother dies before the nymphs are ready to leave, they would 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). the wings will also start to develop, if the wings are present, the forewings are short and thick like elytra or shell over the wins on beetles, covering the hindwings.

Relationship to people

Arixenia esau from the suborder Arixeniina

Hemimerus hanseni from the suborder Hemimerina

Earwigs are fairly abundant and found in many areas of the world, so they are commonly seen, though are mistaken for cockroaches and there is no evidence that they transmit disease to humans or other animals. The pincers are commonly believed by most people to be dangerous, but are actually harmless.

There is a debate whether earwigs are either harmful or beneficial to crops, as they eat both the insects eating the crops and the crops themselves, though it would take a large population to do considerable damage. The common earwig eats a wide variety of food, and also a wide veriety of crops including the leaves and petals. They have been known to cause economic losses in fruit and vegetable losses. Some examples are the flowers, hops, and corn crops in Germany, and in the south of France it has been known feeding on peaches and apricots. the earwigs would attack mature plants and make cupule-shaped bite marks 3mm to 11mm in diameter.

Evolution

The fossil record of the Dermaptera starts in the Late Triassic to Early Jurassic period about 208 million years ago, in England and Australia, and comprises about 70 specimens in the extinct suborder Archidermaptera. The earliest fossils look very similar to recent species but adults have segmented cerci The theorized stem group of the Dermaptera are the Protelytroptera. These insects, which resemble modern Blattodea, or Cockroaches, 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.

Archidermaptera is believed to be sister to the remaining earwig species. This suborder has tarsi with five segments (unlike the three found in the other suborders) as well as unsegmented cerci like Hemimerina and Arixenina, no fossil Hemimerina and Arixenina are known though.

Classification

E.J. Popham's phylogenetic relationship chart

Dermaptera is relatively small compared to the other orders of Insecta, with only about 1,800 species, 3 suborders and 11 families, not including the one extinct suborder Archidermaptera and its extinct family Protodiplatyidae. The actual phylogeny of the suborders remains a topic of debate, however, as all three extant suborders have distinct morphologies yet molecular evidence suggests Forficulina is paraphyletic through the exclusion of Hemimerina. In 1985, biologist E.J. Popham developed a chart, shown on the right, explaining the approximate phylogenetic relationships between different families and suborders of earwigs. His system was based primarily on the characteristics of the earwig's genitalia.

Suborder Archidermaptera †

Protodiplatyidae

Suborder Arixeniina

Arixeniidae

Suborder Forficulina

Anisolabididae

Apachyidae

Chelisochidae

Diplatyidae

Forficulidae

Karschiellidae

Labiduridae

Labiidae

Pygidicranidae

Suborder Hemimerina

Hemimeridae

Arixeniina represents two genera, Arixenia and Xeniaria, with a total of five species in them. As with Hemimerina, they are the blind and wingless, with filiform segmented cerci earwigs. They are ectoparasites of various Southeast Asian bats, preferring guano from the genus Cheiromeles (i.e., "naked bulldog bats"). The overwhelming majority of earwig species are in Forficulina, grouped into nine families of 180 genera, including Forficula auricularia, the common European Earwig. Species within Forficulina have functional wings and are not parasites. The cerci are unsegmented and modified into large, forcep-like structures. Hemimerina also has two genera, Hemimerus and Araeomerus, with a total of 11 species. They are wingless and blind, with filiform segmented cerci. Hemimerina are viviparous ectoparasites, preferring the fur of African rodents in either Cricetomys or Beamys genera.