The native earwig is a very useful beneficial insect, predating on a wide range of other insects and removing important pests such as codling moth and slugs and snails (they eat the eggs). The European earwig is also a useful predator, but it can sometimes build large populations and become a problems by eating plants or invading homes, This phenomena is usually restricted to small areas where there has been large-scale environmental disturbance, such as vegetation clearance or house building in new suburbs. In this article, Tim Marshall provides some useful background information on earwigs and examines some ideas for organic control methods.
Earwigs are members of the order Dermaptera. They are easily distinguished from other insects by the pincer - like forceps at the end of their long abdomen. These forceps, technically called ‘cerci’, are lifted over the body when earwigs are threatened, and can look quite menacing.
European earwig Forficula auricularia is a scavenging insect found in most parts of the world. It is often reported as a pest, although it can also perform some beneficial role in the garden or orchard.
There are native earwigs, such as Labidura truncata or Labidura ripara (common brown earwig). The adults are larger than the introduced species, and the common brown earwig has a distinctive orange triangle behind the head.
Earwigs can be effective predators on a range of soft bodied insect pests, such as mealybugs, coddling moth (larvae) and anything else small enough to be held down by the forceps (including caterpillars much larger than the earwig). Smaller prey are captured with the mouth parts. I have noticed that they particularly like to find egg caches from moths, snails or other small animals and insects.
The forceps are also used by males fighting each other for a mate, and by females defending eggs or young from other predators (including other earwigs).
The native species are particularly fierce predator of caterpillars and other soft-bodied insects and are also much less likely to become a pest.
Apart from size and the orange markings, the native can be separated from the European species by a straighter and less ‘rounded’ shaped forceps.
The six nymph stages (immature earwigs) are similar in appearance to the adult. There is no pupal stage. The adults have wings, which they rarely use.
Earwigs aestivate in communal groups. Aestivate means to shelter from hot weather over the summer, whereas hibernation means to shelter from cold weather over winter (actually earwigs will do both depending on the climate range). They can often be found in colonies under timber, stones or mulch.
Eggs are laid in the top 5 centimetres of the soil. The adults feed mainly at night, and they are most active in spring and autumn.
Earwigs are omnivores with a very wide food range, including other insects, carrion, detritus (rotting vegetable matter) and living plants. They become a pest when high population numbers develop in an area and they attack growing plants, especially tender growing tips, flowers and fruit. They can destroy seedlings overnight and may also invade homes. They will develop large populations after major disturbance reduces biodiversity - removing both competing species and predators which might otherwise control the earwigs. New housing estates sometimes suffer from earwig plagues for three to five years after development.
Though they are a pesky nuisance inside the house, they are harmless to humans, They are a fierce predator of insects, but have not the strength to hold on very tight to human flesh with their forceps. At worst they offer a mild nip. They are best kept well away from small children though, as their love a sheltering spots will lead them to crawl into ears or other personal cavities - hence the name earwig! In fact this is a very rare event but it is still good to take precautions with infants or toddlers.
Remember that earwigs do a great deal of good. Even inside the house they will control cockroaches, spiders and other pests. Because they are visible and because their forceps look fierce, earwigs are often blamed for damage caused by other pests. A magnifying glass and a few minutes spent watching will soon reveal whether they are chewing leaves and stems, or simply scavenging eggs, mites or other prey from the damaged plants. They will definitely feed on fruit opened up by birds and other pests.
Earwigs need shelter during the day and in very hot or cold periods. Good garden hygiene will reduce sheltering sites. Clean up old timber or iron sheets, where they love to congregate.
Traps are an old treatment which exploits their love of shelter and the social tendances of earwigs. The traditional method is an upturned clay pot, either on the ground or on top of a short tomato stake. The stake works well as they love to climb. If left on the ground, prop the pot up on one side with a stone so the earwigs can crawl under. In fact any container will work. An additional trick is to loosely fill the pot with shredded paper or rags, to provide good hiding spots. A variation on this method is to leave hessian sacks or damp rolled-up newspapers on the ground for several days. Lift the sack or paper and shake into the fowl yard, or into a bucket of water with a thin kerosene layer or some liquid soap, if you don’t have chooks.
Hollow bamboo and short lengths of garden hose or plastic conduit also make a good trap.
Beer or other fermenting baits can be used to lure earwigs, in a similar manner to slug traps (see Acres Vol 2 no. 4).
Poultry will eat earwigs, if you have the type of garden which can stand a little light scratching from birds. A good trick is to feed the poultry a lot of greens before turning them out into the garden. They will then be looking for a bit of protein and may leave your plants alone for a while.
Poison baits can be used for very troublesome infestations, and it is better to attract the earwigs to the poison by mixing it with a carrier such as bran than to spray the whole yard or the plants themselves. Derris and pyrethrum are effective.
Insecticidal soaps, such as the potassium soaps readily bought from good garden centres are also effective.
If earwigs are climbing plants to feed on flowers and fruit, use greasy barriers (paraffin or any other greasy substance) on the stems to prevent them from climbing.
Biological controls include birds, lizards, nematodes parasitic flies.