Earwigs are insects that fall under the order Dermaptera. Containing about 2,000 individual species spread over 12 families, earwigs are one of the smaller groupings of insects. They are known for their large cerci—forceps-like pincers protruding from their abdomens.
Despite their intimidating appearance, earwigs are generally non-aggressive and neither sting nor bite. Most of the time, earwigs are content to hide in dark enclosed spaces and keep to themselves. They are capable of delivering a sharp pinch with their cerci when threatened, but even in the largest species, the pinch is non-venomous and rarely strong enough to break the skin.
There are many myths surrounding earwigs that exaggerate their aggression and misrepresent their behavior. Contrary to urban legends, earwigs do not crawl into peoples’ ears, burrow into their brains, and lay eggs. On the extremely rare occasion that an earwig might actually stumble into a human ear, they normally just leave and do not stay for long. The prevalence of this myth is evident in that the various names given to earwigs. In French, earwigs are called “perce-oreilles” (“ear-piercers”) and in German, “Ohrwurm” (“earworm”). Earwigs were first formally classified in 1815 by William Kirby and the oldest known earwig fossils date back to the Jurrasic era 208 million years ago.
Most earwigs have flattened and elongated bodies which measure anywhere from 7-50 mm in length, depending on the species. The largest known species of earwig is the now-thought-extinct Saint Helena earwig which regularly reached lengths of up to 78mm (~3 inches). The shape of the body somewhat resembles that of a winged ant. Earwigs are sexually dimorphic, with males generally having a longer body and more curved cerci. Generally, their bodies are a darker neutral color, such as brown or black. On occasion though, earwigs can be brightly colored in reds and oranges.
Like all insects, earwigs have tri-segmented bodies, consisting of a head, thorax, and abdomen, and 6 legs. Each leg is divided into three smaller segments called the femur, tibia, and tarsal segments. Most species have short leathery forewings that fold and rest on top of the body to cover thin veiny hindwings, similar to the hardened elytra of beetles. Most earwigs are capable of flight but rarely do so. Species of earwig can be differentiated from each other in virtue of the unique folding pattern of the hindwings and how they rest next on the abdomen. Most species have a pair of 10-segmented antennae on the head which is used for sensory purposes. Earwig nymphs are similar in morphology to adults, just smaller and a white-greyish color. Nymphs have shorter antennae and more segments in their body. As they grow, individual segments of the nymph’s body will fuse together into the larger segments present on adults.
The most obvious characteristic of earwigs is their forceps-like pincers protruding from the rear of the abdomen. Earwig cerci are made out of chitin and each pincer-end has two segments. The abdomen is very flexible, allowing the earwig to twist its body to grasp objects with its pincers. Earwigs use their pincers for self-defense. Though fearsome looking, their cerci will rarely cause any serious damage to humans. Some species use their cerci to hold prey still while feeding and it is thought that the cerci play a role in copulation in other species. The cerci can be small, measuring only a few millimeters, but in some species, the cerci can account for half of the body length.
Earwigs are primarily nocturnal, primarily active during the evening and night. They are found on most continents, particularly in the Americas and Eurasia. Despite their present-day commonality in the Americas, it is believed that most earwig species were only first introduced to the Americas from Europe in 1907. In fact, there are only a handful of species of earwig native to North America, such as the spine-tailed earwig (Doru aculeatum) and species under the family Forficulidae. Earwigs mostly live in warm temperate climates and have trouble living in cold, arid regions.
Their slender flat bodies are ideal for inhabiting small openings and crevices. Earwigs prefer tight enclosed spaces because they are, like many cockroaches, thigmotactic—responsive mainly to touch and pressure. Earwigs are omnivorous, and a few are predators. Common earwigs scuttle along the ground, eating plants, fruits, and decaying vegetation. They also feed on small ground-dwelling arthropods, such as aphids, flies, ants, termites, and worms. Earwigs are known to feed on agricultural crops like strawberries, beans, corn, celery, and cauliflower. Their appetite for common food items has made it so earwigs are considered agricultural pests some places in the world. The natural predators of earwigs include birds, mammals, amphibians, lizards, spider, and centipedes. Earwigs are also vulnerable to a number of parasitic organisms, like roundworm and fungi. Earwig eggs are particularly vulnerable to parasitization.
A handful of earwigs are epizoic, meaning that they live on the exterior of another living animal. Species in the Arixeniina and Hemimerena families are known to live on the outside skin of rodents like bats, rats, and mice. Others species of earwig find their dwelling near mammal nests, where they can feed on animal material and other arthropods that live near mammal nests. Epizoic species of earwig are generally not considered parasitic as they tend to benefit their host organism, or at least not harm them.
Like most insects, earwigs go through a series of developmental stages throughout their lives. From egg to adult, earwigs go through 4 to 6 developmental phases called instars. The progression through these stages is gradual and the insect morphology is similar throughout these phases. Unlike insects such as caterpillars or fleas, earwigs do not have a distinct pupa stage where they undergo a dramatic metamorphosis into adults. Earwig larvae are morphologically similar to adults, but lack wings and functioning reproductive organs. In general, the lifespan of an earwig from egg to adult is approximately 1 year.
The mating season normally begins in the autumn and continues into the early winter. During mating, males will compete with other males for female attention by battling with their cerci. Males will also use their cerci in a form of courtshipOnce mating pairs have been selected, both male and female will burrow into underground chambers and copulate. After copulation, the sperm remains in the female for sometime before the eggs are actually fertilized. Once fertilized, the females lays her eggs in a brood of 20-80 eggs. Some earwigs actually give live birth to their young, which are fed by a placenta-like mass.
Earwigs are one of a few species of non-social insect that take an active role in raising their young. Earwig mothers will normally stay with their eggs, giving them warmth and protection until they hatch. She will also routinely clean the egg during this period. Eggs take about 7 days to hatch. Once hatched, the mother earwig will protect her nymphs and feed them regurgitated food. When the mother earwig is not present, nymphs will nourish themselves by consuming each other’s feces, a behavior known as allo-coprophagy. Simply being around others causes the nymphs to produce more feces, an evolutionary strategy for survival. Nymphs have also been observed to sneak into the nest of other earwig broods and attach themselves to the anus of an adult. Both mothers and nymphs have been observed to engage in cannibalism of their dead; larval nymphs will even eat the mother is she dies before they mature into adults. After their 5th molting, the nymphs become adults and leave the nest to seek food and opportunities to reproduce.
Humans And Earwigs
Humans have known about earwigs for a long time. The first recorded mention of earwigs in history dates back to the first century AD, by Pliny the Elder in his book Naturalis Historia. Pliny wrote that earwigs commonly would invade a human’s ear canal to lay eggs and burrow deep into the skull. Descriptions of earwigs in scientific literature that referenced their putative fondness for brain-burrowing persisted up to the 19th century, and many people today still believe that earwigs have a habit of crawling into ears. The reality is much more mundane though. Earwigs can sometimes find their way into a human ear, but so can other insects like flies or ants. Despite their name, earwigs are not particularly prone to any ear-crawling behavior.
Earwigs are considered as agricultural pests by any farmers, but in some cases can actually be beneficial for crops. Though they eat common crops, they also eat insect and arthropods that feed on those crops too. This realization has led to a debate among farmers over whether earwigs should be considered universally detrimental, or if they could be desired in some cases.
Many people fear earwigs due to their large and painful-looking cerci. Earwigs, however, are not aggressive and won’t attack unless threatened. Even if they do lash out, their cerci are non-venomous and the pinch rarely breaks the skin. Wound treatment is the same that is recommended for any minor scratch.