How much do you know about earwigs? Here we take a look at them in detail.
Earwigs are certainly one of those occasional pests that most people will ignore, but some will get very anxious about them, probably due to their scary appearance and their ‘pincers’ at the end of their body. On occasions, earwig populations can reach infestation levels. So how much do you know about earwigs and how to control them?
Firstly the name – the Australian museum reports various options regarding its origin. Certainly, there is little evidence that earwigs have a tendency to crawl into people’s ears when they are asleep! A more likely alternative is that ‘earwig’ is derived from the Anglo Saxon (old English) words, ‘eard’ meaning soil and ‘wicga’ meaning insect; words which give us some clues as to its biology.
Most earwig species are omnivores eating a range of animal and plant materials. They commonly live in the leaf litter where they eat decaying plant material. However, some species are obligatory herbivores and some are predatory. There are 85 species of native Australian earwigs that have been described so far, including the largest species, the Australian giant earwig (Titanolabis colossea) which grows up to 50 mm long. The different species range in size and colour, from yellow through to brown and black. There are also some additional introduced species. One of these species, the European earwig, Forficula auricularia, is a significant pest of plants in gardens and can be a common pest in suburban areas.
Earwigs belong to the Dermaptera family, which describes their leathery forewings. The fact that the adults of most earwigs have wings and can fly is perhaps a surprise to many, as they are generally seen crawling on the ground. Although the leathery wing covers seem small, when their wings unfold, they expand to ten times the size! The mechanics of this origami and the strength of the wing is the subject of engineering studies.
The forceps-like pincers at the end of their body are actually hardened cerci, with the shape and size varying between species. These pincers have a variety of uses, depending on species – for holding prey, for defence and even for helping to pack up their large wings! They don’t inject any venom and are essentially harmless to humans, although they can excrete a noxious chemical when threatened.
Earwigs exhibit incomplete metamorphosis, which means the nymphs look similar to the adults, although they lack wings. They go through four or five moults before becoming adults. The interesting aspect of their life cycle is that the female actually cares for the eggs and young nymphs, which is unusual in a non-social insect. The female digs a shallow burrow under leaf litter to lay her eggs (pictured above) which are kept clean by regular licking. Upon hatching, the female will feed the nymphs up to the second or third instar.
Females of the European earwig build their burrows and lay 20-80 eggs at the end of autumn. Eggs hatch in 4-6 weeks and each stage takes 4-6 weeks to develop, so early instars may not leave the nest until late winter. Once these have hatched, occasionally the female will lay a smaller second batch in spring. European earwig numbers will be at their maximum in spring. In contrast to many other earwig species, European earwigs can aggregate a bit like cockroaches, and under ideal conditions – plenty of food and moisture – significant populations can develop, year on year.
Earwigs, especially the European earwig, are regarded as a pest of crops and agricultural areas as they will cause damage to seedlings and soft fruit. The damage they cause is similar to caterpillars – irregular holes in the middle of leaves or chewed areas around the edges, but without the webbing that caterpillars may create. Earwigs can become a problem in the home vegetable garden.
Earwigs are nocturnal and are attracted to light, which means they are commonly encountered after dark, having entered the building to move towards the light. This is more likely to occur during periods of drought when they may leave dry leaf litter looking for a more moist environment.
Eliminating an earwig problem is primarily about environmental management. The first step is to ensure there are no heavily watered garden beds or vegetable gardens immediately next to the house – eliminating such areas will obviously have a range of pest prevention benefits (not the least in making the home less attractive to termites!). With any earwig populations then likely to be further away from the house, the number of earwigs accidentally entering the home will reduce significantly. Well fitted insect screens and excluders should prevent most invaders.
The specific use of chemicals to control earwigs around homes is very limited, as the general pest concentrates do not have specific label claims against earwigs, although there are some crop and garden products which have specific claims. (A search on Pubcris for potential products is a good starting point.) However, for most situations around buildings the application of a general pest treatment to the perimeter of the home targeting the common pests (ants, spiders, cockroaches) will also provide protection against earwigs. However, if a more specific treatment is required to protect a home vegetable or fruit crop, a specific crop product should be sourced and instructions followed.
For homeowners who do grow vegetables or fruit at home, they can consider setting up traps to monitor earwig numbers. A simple pitfall trap – consisting of a can sunk into the ground, containing fish oil – can be very effective. If several traps are set, they can even be effective at keeping numbers in check in small areas.