Earwigs are scary-looking beetles with a pincer at the end of the abdomen. Ancient Anglo-Saxon legend says that if one crawls into your ear, it will burrow into your brain, lay eggs and cause insanity. Of course, this is complete nonsense: Earwigs almost never climb into people’s ear canals, and if one did, it would not enter the brain. If by some astounding coincidence one got in the ear, the best thing to do would be to shine a light into the canal. This would probably convince the earwig to leave of its own accord. (Earwigs are nocturnal and avoid bright light.)
The common name for earwig in at least six European languages includes the word ear. Many scholars believe earwig comes from earwing, since an earwig’s hindwing when unfurled resembles a human ear. Others think ear- might occur in the name because the pincers resemble instruments used to pierce human ears.
Earwigs do not bite, but they can pinch with their pincers if they feel threatened or are picked up. They do not attack but will pinch to defend themselves. The pinch causes little harm to humans. They also use their pincers during mating and to grab prey and can twist their abdomen over their head or sideways to pinch an enemy, often another earwig. In this way, male earwigs assert their dominance over other males during mating season. . Male pincers are rounded; female pincers are straight.
The reddish-brown European earwig (Forficula auricularia) is the most common in Massachusetts. It is about an inch long. Earwigs need dark, damp conditions to survive, so during the day they hide under logs or leaves, in cracks and crevices, under flowerpots and in woodpiles, under bark and in shrubs. They come out at night to feed and scavenge. They are omnivores who eat plants (including dahlias, zinnias and butterfly bushes, lettuce, strawberries and potatoes. They also feed on silks in ears of corn.) They eat spiders and small insects, especially aphids.
Earwigs fold their hindwings in a more compact way than any other insect. When they fly, they expand their wings more than 10 times the size of the folded wings. This folding ratio is the highest in the animal kingdom! The insects do not use their muscles to fold or unfold their wings. Instead the wings pop open or close by themselves, locking up for flight and unlocking to fold. The wing folds are bended (not straight) and have springlike properties with two stable configurations. This allows the wings to lock when completely open or completely folded. Scientists are studying how earwigs manage this complicated feat (especially since earwigs hardly ever fly). There may be applications for this wing-folding mechanism in pop-up tents, folding electronics, soft robots, remote spacecraft, architecture, aerospace and mechanical engineering.
Earwigs mate in late summer. Then they dig an underground cell (nest) in which a male and female overwinter in a dormant state. In late winter, the female lays white eggs in the nest and drives the male away. Unlike most insects, she takes care of the eggs: She cleans them with her mouth and pincers to remove parasites and fungi spores. She moves them to areas with the most appropriate humidity and temperature. And if that wasn’t enough, she also chases away intruders. She keeps the eggs in a pile until they are ready to hatch. In spring when they are close to hatching, she spreads them out into a single layer.
The hatchlings, called nymphs, are translucent white and look like small wingless adults. Then the female opens the underground nest, and the hatchlings forage on the ground at night, returning to the nest during the day. For about a month (until their first molt), the female also regurgitates food for the nymphs and brings them food. The hatchlings follow her around in a little entourage.
The mother and nymphs line the nest with their feces. (Many insect species remove feces from nests, but earwigs do not.) Scientists have determined that when food is scarce, earwig survival is enhanced because the nymphs eat the feces of sibling earwigs. Even when food is not scarce, earwigs always consume some feces, though – which may transfer helpful gut bacteria among families and have other unknown benefits.
After they molt a second time, the nymphs no longer return to the nest, and find their own daytime hiding places. By August, the nymphs have molted several times and reach their adult stage. (In some species of earwig – but not our common European earwig – if the mother dies, her progeny devour her.)
Most insect species reject foreign offspring, but earwigs do not. If foreign eggs are placed in her nest, she raises them like her own. You might think this means she cannot tell the difference between her eggs and foreign eggs, but this is not the case. Earwig mothers lick eggs to apply chemicals to the surface that keeps the eggs from drying out. These chemicals also signal to the mother that an egg belongs to her. It is not known why earwigs tend foreign eggs like their own, but females that tend eggs lose less weight than those that do not. (It’s possible that the females eat some of the eggs, but this is not known for sure.)
The European earwig is, as the name implies, native to Europe but first noted in Seattle in 1907. It reached Rhode Island by 1911, New York in 1912 and most other northern states in the 1930s. It prefers temperate climates, so it is less common in the Southeast and Southwest.
If you bother these insects, they can emit a foul smelling yellowish liquid that some describe as smelling like rotting meat or feces. Others describe it as having an acrid smell. This scent is probably a defense mechanism meant to deter predators such as birds and reptiles. Earwigs produce another scent that humans cannot detect at all, but it attracts other earwigs. It is this scent that helps earwigs cluster together in sheltered areas where they hide during the day.
So if you should happen upon an earwig, know that although it looks fierce, it is harmless and will likely run away. Unless you pick it up. Or you are an aphid.
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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
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