Dermaptera - earwigs, forkytails

The earwig body

Earwigs are easily recognised by their posterior cerci which are modified as pincers which are more curved in mature males than females (see Forficula auricularia on the right and below, which shows a whole male and the pincers of a female, and the male in the photograph below).

Males do sometime use the pincers against each other when fighting over food or females, but mostly they are used in defence, predation, courtship and grooming. The pincers cannot harm humans.

Their front wings are small and hard and cover their rear wings which are very elaborately folded beneath. In some species, e. g. Forficula auricularia the tips of the rear wings are visible peeping out from below the fore wings making it look like the insect is wearing a waistcoat. The rear wings are large and semi-circular when fully open. They have the texture of skin, which explains their name, derm = skin, aptera = wings in Greek. Most of the winged species fly only rarely, and other species are wingless.

The antennae are long and simple. They have 2 compound eyes, but no ocelli.

The nymphs resemble the adults, but with slender pincers which thicken and increasingly take on the adult shape with each moult.

Moulting. There are usually 3 or 4 moults and the nymphs reach adulthood in late summer. It takes around 6 - 7 hours for the exoskeleton to become hard and darken.

White earwigs are sometimes seen. These are just recently moulted individuals whose exoskeleton has not hardened and taken on the normal colourations.

Earwig behaviour

Earwigs are active mainly at night, and are omnivorous scavengers. There was an old belief that earwigs entered the human ear and bit through the eardrum. They do occasionally enter the human ear, especially from straw mattresses as they seek out narrow, dark crevices to rest in during the day, but they do not harm us in any way.

Earwigs cannot rest comfortably unless both upper and lower surfaces of their bodies are touching something - this means they are thigmotactic. Gardeners take advantage of this behaviour by trapping them in straw-filled upside-down flowerpots. Though once found there is no need to destroy them, just put them somewhere away from you beloved blooms - the compost heap is a good place and they will help in breaking down the vegetable matter into humus for you.

The females are very attentive parents. Looking after their eggs for months - at least until the nymphs first moult, licking them and keeping them clean and free from fungal infections and parasites, and defending them against predators.

Forficula auricularia

Forficula auricularia, left, is the most common earwig in Europe, and is found in nearly all the temperate regions of the world. The male is shown in the drawing and photograph above with the more slender pincers of the female on the right. It is found in most habitats. The rear wings always protrude slightly below the fore wings. The adult body length is 10 - 14 mm plus another 4 - 9 mm for the pincers. The body is brown with a slightly darker head and lighter legs. It has wings, but rarely flies.

Mating and reproduction of Forficula auricularia

It has been found that females prefer to mate with males with larger pincers. At the end of summer the female mates and digs a nest, often beneath a stone, and usually with two chambers. Stones are preferred as the stone stores heat, so by moving her eggs around in the chambers she can regulate the temperature of her eggs.

The male may help with the digging of the nest, and stay with her until she is ready to lay the eggs, but she usually ejects him before laying, sometimes using force. She seals up the entrance to the nest, and then she lays 20-50 eggs.

The eggs are oval and white 1.0 by 1.25 mm. She looks after them all through the winter without leaving them to feed. When she detects the eggs are about to hatch she spreads them out on the floor of the nest in a single layer, previously they would have been clumped in a pile.

When the young do eventually hatch in the early spring she continues to feed them for a while. And the young nymphs huddle up under her body. She catches any strays in her mouthparts and places them beneath her. When first hatched the nymphs stay in the the nest and the mother brings food to them. Only now does she leave them to go out foraging for food for herself and perhaps as many as 50 young.

On returning to the burrow she regurgitates food for the nymphs who nuzzle her mouth to show their hunger. After their first moult the nymphs leave the nest, but the mother continues to feed them for a while. However once the young nymphs have left their mother to fend for themselves she no longer recognizes them if they ever meet again.

British earwigs (4 native and 3 introduced species)