Signs of Summer 7: Earwigs!

photo by Niels Heldenreich Flcikr

photo by Niels Heldenreich Flickr

Everyone should go outside and pick up one of the potted plants on your porch or deck. It is almost certain that under some (or all) of these plant pots will be creatures that are nobody’s favorite insect: European earwigs!

The European earwig (Forficula auricularia) is a native, insect species of Europe, Northern Africa and Western Asia that has been accidentally introduced into a number of temperate and tropical countries around the world. Its first recorded appearance in the United States was in Seattle, Washington in 1907. It was likely brought to this country in a shipment of flowers, fruit, or vegetables. In the hundred years since it arrived in the United States, the European earwig has found its way to almost every region and every state in the country.

There are twenty-two species of earwigs in the United States. Twelve of these species (like the European earwig) are alien exotics, and ten are endemic (“native”). Only four of these twenty-two species, though, are classified as pest (or potential pest) species. Most of the earwig species in the United States actually are quite beneficial acting as shredders and comminuters in the soil decomposer community and as biological control agents (predators) for a variety of insect pests. The European earwig is classified as a pest species, but it is also acknowledged that it can also be an active predator of crop damaging aphids, caterpillars, beetles, and midges. Its role as a pest controlling agent is especially important in organic orchards and farms. In Pennsylvania, the European earwig is the most commonly found “pest” earwig species.

The name “earwig” has a long and extremely non-scientific history. It is derived, according to the Oxford English Dictionary (and who could argue with that?), from the Old English word “earwicga” which translates as “ear wiggler.” There is an ancient myth that these very harmless (to humans, anyway) insects have the ability to crawl up the ear canal of a human and then eat their way into that unfortunate person’s brain. None of this is true, and it is very unclear why anyone would have thought that it was or why this myth would persist over many hundreds or thousands of years! There have been, though, some interesting fictional adaptations of “earwicga” myth in literature and in science fiction television shows and movies.

The European earwig is a little over one half an inch long (females are larger than males). They have a dark, red-brown body, a reddish head, yellowish legs, two long antennae, two membranous flight wings (which it seldom uses) tucked under the hard, protective forewings, and two very distinctive cerci (“pinchers”) on the end of its abdomen. The shape of the cerci differs in males and females with females having straight cerci and males having curved cerci. These cerci are used to grab and secure prey and also, in males, as weapons in mating competitions.

European earwigs are nocturnal and spend the day in dark, moist places (like spaces under rocks, logs, surface vegetation, flower pots, leaf litter etc.). One frequently mentioned method of bio-control of earwigs is to make sure that your property is free of these potential daylight refuges. Earwigs are omnivorous and will consume plant materials (both living and dead), aphids, spiders, insects, insect eggs. They will consume garden plants and a wide variety of fruit and vegetable crops but, very interestingly, seem to do so when potential prey (like aphids) are not present in sufficient numbers. European earwigs also accumulate inside human habitations and can work their way into almost any open space or crevice. They can consume stored food products (flour, bread, cereal, crackers, etc.) and befoul clothes, books, laundry and more with their odiferous secretions.

European earwigs are solitary organisms and have no social behaviors or communication systems. Males and females meet up once a year, though, in order to mate. Males find females via pheromones that the females excrete in their feces. Males attracted to the pheromone then compete with each other for the attention of the female. It is thought that body size and especially cerci size are the critical variable in a male’s reproductive success. Mating takes place in early autumn.

Photo by Tom Oates Wikimedia Commons

Photo by Tom Oates Wikimedia Commons

The female then digs out a brood nest and lays her clutch of thirty to fifty eggs. This nest will also serve as the hibernation nest for the female and also for the male. The female will tend to the eggs stacking them up and then spreading them out making sure that fungi do not grow on them and protecting them from possible predators. The eggs will hatch in the spring and the first nymphs that emerge (the first “instar”) will remain in the nest and continue to be cared for by the female. The female guards and feeds the nymphs (via regurgitated plant materials) throughout the first instar stage (which is about the first month of life). This level of maternal involvement with offspring is very unusual in insects!
There are four nymphal stages in earwigs. In the second instar stage the female opens up the nest and the nymphs begin to go out at night to search for food. These second instars, though, tend to (or at least try to) return to the nest during the day. By the third instar stage, though, the nymphs have completely left the nest and move freely about the soil and litter habitat searching for food by night and seek out their own daylight refuges by day. These nymphs develop into adults in the late summer or early fall and then mating occurs and the cycle begins all over again.

Some female earwigs lay a second clutch of eggs after the second instar nymphs have left the nest. This second batch of eggs hatches and marches through the four nymphal stages very rapidly in the warm temperatures of summer and matures into adult earwigs at the same time as the cohort that hatched from the overwintering clutch of eggs.

Earwigs are preyed upon by many species of birds (including chickadees and nuthatches) and are also eaten by a number of amphibians (especially toads). They are also parasitized by the parasitoid fly Bigonicheta spinopennis and susceptible to numerous bacterial and fungal infections.

So, when you turn up a few earwigs in a flower pot or under a rock or log, try not to be completely grossed out! I think that I have received over the years more phone calls and emails about earwigs (“What are they?” “What do they do?” “Are they from outer space?”) than about any other insect (except maybe for brown, marmorated stink bugs). These insects may be doing a great deal of good out in their soil and litter ecosystems, and they are some of the most devoted and attentive mothers in all of Class Insecta! Let’s give them a little respect, at least.

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