Fossil range: 208–0 Ma Late Triassic to Recent
|Common earwig, Forficula auricularia|
De Geer, 1773
Earwigs, sometimes called pincerbugs, make up the insect order Dermaptera. The order is relatively small among other insect orders, with only 1,800 recorded species in 12 families, found throughout the Americas, Eurasia and Australia. Typical earwigs have characteristic cerci, a pair of forceps-like pincers on their abdomen, and membranous wings folded underneath short forewings, hence the literal translation of the scientific name for order "skin wings". Some groups within the earwig order are tiny parasites on mammals and lack the typical pincers. Earwigs can fly, but rarely do.
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 are commonly blamed on earwigs, especially the common earwig. However, the harmfulness of earwigs to foliage 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. An uncommon behavior in other insects, many earwig species display 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 Archidermaptera dating back to the Late Triassic. Many orders of insect have been theorized to be closely related to earwigs by many authors, though Grylloblattaria is the most likely. The order of earwigs, Dermaptera, is still under dispute over its phylogenetic relations to other groups.. Those specimens are now included in the extinct suborder
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 ēare, which means "ear", and wicga, 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, harmlessly, into the human ear canal.
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 (ear-piercer, literally pierce-ear); Danish ørentviste; Slovak ucholak (ucho = ear, lak = scare); Romanian urechelniță; Bulgarian уxолазка (уxо = ear, лазка = crawler(f.)); and Hungarian fülbemászó ("crawler-into-the-ear"). 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.
Most earwigs are flattened (to fit inside tight crevices, such as under bark) with an elongated body generally ranging from 7 to 50 mm, though some can grow longer, such as the Saint Helena earwig which reaches 80 mm 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 antennae are thread-like with at least 10 segments or more.:738–739
The forewing is a short oblong leathery plate used to cover the forewing 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.
Earwigs are mostly scavengers, but some are omnivorous or predatory.:739–740 The abdomen of the earwig is flexible and muscular. It is capable of manoeuvring 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.
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. 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.
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 patrolling 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. During the summer they can be found around damp areas such as near sinks and in bathrooms. Earwigs tend to gather in shady cracks or openings or anywhere that they can remain concealed during daylight. Some people erroneously believe that earwigs crawl into people's ears at night and make burrows. Earwigs are harmless to people. Picnic tables, compost and waste bins, patios, lawn furniture, window frames, or anything with minute spaces (even artichoke blossoms) can potentially harbor them. The only insect predators that prey on the earwig are parasitic species of Tachinidae, or tachinid flies, whose larvae are endoparasites of the earwig. The eggs and nymphs are also cannibalized by other earwigs.
Earwig are hemimetabolous, or undergo incomplete metamorphosis, meaning they develop in a series of 4 to 6 molts. The developmental stages between molts are called instars. Earwigs live for about a year from hatching. They start mating in fall, and can be found together in the fall and winter. The male and female will live in a chamber in debris, crevices, or soil 2.5 mm deep. After mating, the sperm may remain in the female for months before the eggs are fertilized. From midwinter to to early spring, the male will leave, or be driven out by the female. Afterward the female will begin to lay 20 to 80 pearly white eggs in 2 days. Some earwigs, those parasitic in the suborders Arixeniina and Hemimerina, are viviparous (give birth to live young); they would be fed by a sort of placenta.:739–740 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.
Earwigs are among the few non-social insects species that show maternal care. The mother will pay close attention to the needs of her eggs, such as warmth and protection, though studies 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 they would eventually be rejected as they do not have the proper scent. The mother will also vigorously defend the eggs from predators, not eating unless an egg goes bad.:740 Another distinct maternal care unique to earwigs is that she will continuously clean the eggs to protect them from fungi. Studies found that the urge to clean the eggs persists for days after they are removed; when the eggs were replaced after hatching, the mother continued the urge to clean them up to 3 months.
The eggs hatch within 7 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.:740
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 hindwings of an earwig are made of elytra—the same material that beetles' shells are made of.
Earwigs are fairly abundant and can be found virtually everywhere, especially throughout the Americas and Eurasia. The common earwig was introduced into North America in 1907 from Europe and now occur throughout North America, but tend to be more common in the southern and southwestern states.:739 The only native species of earwig found in the north is the Spine-tailed earwig (Doru aculeatum):144, found as far north as Canada, where it hides in the leaf axils of emerging plants in southern Ontario wetlands. Though two to three other families can be found in North America, including Forficulidae (Doru and Forficula being found there), Labiidae, Carinophoridae, and Labiduridae.
Few earwigs survive winter outdoors in cold climates. They can be found in tight crevices in woodland, fields and gardens.:739 Out of about 1,800 species, about 25 occur in North America, 45 in Europe (including 7 in Britain), and 60 in Australia.
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. The most likely, and most closely resembling, related order of insects is Grylloblattaria, theorized by Giles in 1963. However, other arguments have been made by other authors linking them to Phasmida, Embioptera, Plecoptera, and Dictyoptera.
Archidermaptera is believed to be sister to the remaining earwig groups. This suborder has tarsi with five segments (unlike the three found in the other suborders) as well as unsegmented cerci like Hemimerina and Arixenina; however, no fossil Hemimerina and Arixenina are known. 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.
Some evidence of early evolutionary history is the structure of the antennal heart, a separate circulatory organ consisting of two ampullae, or vesicles, 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.
The characteristics which distinguish the order Dermaptera from other insect orders are:
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 are free-living, have functional wings and are not parasites. The cerci are unsegmented and modified into large, forceps-like structures.
The first epizoic species of earwig was discovered by a London taxidermist on the body of a Malaysian hairless bulldog bat in 1909, then described by Karl Jordan. By the 1950s, the two suborders Arixeniina and Hemimerina had been added to Dermaptera.
Arixeniina represents two genera, Arixenia and Xeniaria, with a total of five species in them. As with Hemimerina, they are blind and wingless, with filiform segmented cerci. Hemimerina are viviparous ectoparasites, preferring the fur of African rodents in either Cricetomys or Beamys genera. Hemimerina also has two genera, Hemimerus and Araeomerus, with a total of 11 species.
Dermaptera (= Euplecoptera, Euplexoptera, or Forficulida) 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 phylogeny of the Dermaptera is still debated. The extant Dermaptera appear to be monophyletic and there is support for the monophyly of the families Forficulidae, Chelisochidae, Labiduridae and Anisolabididae, however suggests that Forficulina is paraphyletic through the exclusion of Hemimerina which should instead be nested within the Forficulina.
Suborder Archidermaptera †
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 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 (e.g., basements) rather than typical bedrooms.
There is a debate whether earwigs are either harmful or beneficial to crops, as they eat both the insects eating the foliage (e.g, aphids) and the foliage itself, though it would take a large population to do considerable damage. The common earwig eats a wide variety of plants, and also a wide variety of foliage including the leaves and petals. They have been known to cause economic losses in fruit and vegetable crops. Some examples are the flowers, hops, and corn crops in Germany, and in the south of France it has been observed feeding on peaches and apricots. The earwigs would attack mature plants and make cup-shaped bite marks 3 mm to 11 mm in diameter.
Subordines: Arixenina - Hemimerina - Forficulina - †Archidermaptera - †Protelytroptera - Incertae Sedis
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