Earwigs are insects which entirely compose the order Dermaptera, which features roughly 2,000 species in 12 families.
Earwigs have slender flattened bodies, bead-like antennae, and are easily recognized by the pair of large pincers at the tip of their abdomens, called cerci. Adult males have ten abdominal tergites; females, eight. Some are wingless, but in most the forewings are represented by short leathery covers called tergmina, under which the hind wings (if present) fold in a unique fan-like fashion, leaving a chitinized triangular part exposed. These forewings are rarely used, but contribute to these bugs’ scientific name “skin wings.” Earwigs are found on all continents except Antarctica.
Those species of earwigs known to exist in Southern California include the Euborefliua annulipes, Anisolabis maritima, Forficula auricularia, Euborellia cincticollis and two rare flying variety, the Labia minor and Labidura riparia.
Earwigs are mostly nocturnal and 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 sometimes commonly blamed on earwigs, though the bugs offer benefits to crops, as they eat both the foliage and the insects eating such foliage, such as aphids.
Males and females differ in forcep size, with males having much larger one with a stronger curve, while females have smaller, straighter forceps with a slight curve at the end. Earwigs use these forceps to assist in predation, defense, sexual selection, courting and mating, and wing folding.
Earwigs live for about a year from hatching. They start mating in the autumn, and can be found together in the autumn and winter. The male and female will live in a chamber in debris, crevices, or soil about an inch deep. Nests are essential for protection from the environment and predators, and are needed for the success of their offspring’s survival. Special nests are dug for molting, feeding, and egg laying. A suitable nest is chosen and dug out by the female under a rock or tree bark. During mating, the male and female will cohabit for three months or more. Sometime after fertilization, the female, as the primary caregiver of her young, will become hostile to the male while in the brooding chamber. From midwinter 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 two days.
Earwigs are among the few non-social or subsocial insect species that show maternal care. The mother will pay close attention to the needs of her eggs, such as warmth and protection. The mother will also faithfully defend the eggs from predators, even forgoing feeding herself during this period. Another distinct maternal care unique to earwigs is that the mother continuously cleans the eggs to protect them from fungi. While the female is laying her eggs, she grabs them and cleans them of any fungi or dirt one by one as they are laid. Upon finishing this chore, they will lay on top of the eggs much like a hen. Studies have 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 to clean them for up to three months. Under normal conditions, the female continues to groom the eggs and stay on guard over them for 10 days until they begin to hatch. At this time the mother goes in search of food for her young, and continues feeding and grooming them until they leave the nest themselves two to five days later. Some females get lost returning to their brood and start caring for another individual clutch as they are not able to distinguish between their own young and another’s. The young will go on to dig their own nest for molting, taking anywhere from 4 to 50 days to reach the next instar.
Earwigs are hemimetabolous, meaning they undergo incomplete metamorphosis, developing through a series of 4 to 6 molts. The developmental stages between molts are called instars.
Earwigs are mostly scavengers, but some are omnivorous or predatory. The abdomen of the earwig is flexible and muscular. It is capable of maneuvering as well as opening and closing the forceps.
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 will typically result 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.
Earwigs are regularly preyed upon by birds, and like many other insect species they are prey for insectivorous mammals, amphibians, lizards, centipedes, assassin bugs, and spiders. European naturalists have observed bats preying upon earwigs. Their primary insect predators are parasitic species of Tachinidae, or tachinid flies, whose larvae are endoparasites. One species of tachinid fly, Triarthria setipennis, has been demonstrated to be successful as a biological control of earwigs for almost a century. 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.
Primary predators on earwigs in Southern California are ants, as they prey on unattended eggs. Overlap of predation does occur between these organisms, though, as the earwigs prey on the ant eggs as well. The effect of ants on earwigs seems to be greater than the reverse relationship, as populations of earwigs increase if the ants decrease.
The earwig’s observed prey include largely plant lice, but also large insects such as bluebottle flies and woolly aphids. Plants that they feed on typically include clover, dahlias, zinnias, butterfly bush, hollyhock, lettuce, cauliflower, strawberry, blackberry, 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.
Once earwigs become adults, the individuals will live for only three to five months, and begin courting immediately. This is done by a feeling of antennae, and mutual grabbing of each other’s abdomens with their forceps until copulation occurs. Among the Labidura riparia species of earwig, two to three generations will occur in the span of a year, with the last generation hibernating underground through winter.
Earwigs are fairly abundant and are found in many areas around the world. Because of elements of their appearance, they are sometimes erroneously associated with cockroaches. 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 or no harm to humans. Earwigs have been rarely known to crawl into the ears of humans, but they do not lay eggs inside the human body or human brain.
From Wikipedia, https://www.terminix.com, https://bugguide.net/node/view/2709