Biology and Control of Earwigs

One of the most common pests which occasionally invade structures is the earwig. The word earwig is believed to be derived from the Anglo-Saxon word earwicga, which means "ear creature." This name comes from a mistaken belief that earwigs enter peoples’ ears and bore into their brains.

Of the approximately 15 species of earwigs found in the United States, only four or five are common pests. Most of these pest species are imported, having been introduced at one point or another during the last 100 years. The European earwig, Forficula auricularia, appears to have been introduced at least twice on each coast in the early 1900s. Spread of this earwig, as well as other species, to different regions of the United States has been almost entirely by the hand of man. Earwigs hide in many items which have been shipped throughout the country.

Earwigs are of concern as a nuisance pest only. They do cause damage to plants by feeding on leaves and flowers. This damage, however, is generally light and of no danger to the plant’s health. These pests can sometimes build up in large number around buildings and enter through foundation cracks and through windows and doorways.

Some species are capable of flight and are attracted to exterior lights. This often results in attracting large numbers of earwigs to a single structure, causing significant problems indoors.

This article will examine the earwig species of most importance and discuss methods for management of their populations around structures.

BIOLOGY. Earwigs are easily identifiable by the forceps-like appendages, called cerci, which extend from the end of the abdomen. These cerci can sometimes be quite large and formidable looking.

Earwig behavior is somewhat similar to that of cockroaches: they like to congregate together, and they clean their appendages with their mouthparts.

The female earwig exhibits maternal care for her eggs and young offspring, a behavior rare among insects. The female digs a small chamber in the soil under a rock or leaf litter. She deposits her eggs and then carefully watches over them, keeping them moist by "licking" the eggs frequently. When the eggs hatch, the female seals the chamber for a couple of days to keep the young nymphs confined and protected. She will occasionally leave to find food which is used to feed her young. He nymphs remain in the chamber until after their first molt.

Earwigs are omnivorous, feeding on decaying or live vegetation as well as live and dead insects. The forceps (cerci) are used in self defense and to hold live prey while feeding. Earwigs have never been observed using their forceps in mating as some persons have believed.

• European earwig, Forficla aricularia: The European earwig is by far the most widespread earwig in the United States. It is also found in southern Canada. They survive best in cool, moist climates and are found in arid areas, such as Southern California, only where plenty of moisture is present.

The male European earwig has two forms, one with a large pair of cerci and another form with a smaller pair of cerci. The female’s cerci are small with no teeth along the inner margins. The color is a reddish brown, and the wing covers, legs and antennae are a paler color. Adult European earwigs are capable of flight, but usually travel by walking.

Outdoors, this earwig lives in mulch, dead limbs and stumps, firewood piles, leaf litter and any area which contains sufficient moisture. Under the right condition, hundreds of earwigs may congregate around a single structure. This author collected more than 600 earwigs in Columbus, Ohio, from under wooden steps behind a house. Hundreds of earwigs were also found living nearby in the crack between the soil and the foundation and in a dead section of a tree 2 feet off the ground. This home had a history of earwig problems for several years.

A survey reported in the textbook Urban Entomology reveals that in California, earwigs are ranked as one of the top six pests encountered by PCOs. This past summer, European earwigs became such a problem, the Chicago Tribune devoted a front page story to the problems created by this pest.

• Striped earwig, Labidura riparia: The striped earwig is also known as the riparian earwig or the shore earwig. This earwig is now widely distributed throughout the southern states and parts of Arizona and California.

This is one of the larger earwigs, about 20-25 mm in length. The color varies from pale brown to a darker reddish brown. The abdomen is usually banded, and the cerci are yellowish to a reddish brown and are darker near the tips. The male’s cerci are generally elongated and are conspicuously toothed.

Striped earwigs live in subterranean burrows beneath rubbish, mulch and turf. They are predatory in nature but are also scavengers, feeding on any food they encounter, including pet food and dead insects they have not been observed to damage plants as does the European earwig. This earwig flies and is attracted to outdoor lights.

• Ringlegged earwig, Euborellia annulipes: The ringlegged earwig is widely distributed throughout the United States and, next to the striped earwig, is the most common pest earwig in Florida. This earwig is wingless and dark brown to black in color. The legs are yellowish with rings present on the femora and tibia. The cerci are small and rather nondescript.

The ringlegged earwigs has been reported as a pest in flour mills, breweries and meat packing plants. It has been found damaging the roots of plants in greenhouses and nurseries. It also acts as a carrier of certain endoparasites of fowl in Hawaii.

OUTDOOR CONTROL. In most situations, earwigs are only an occasional invader, occurring only in small numbers around a structure. The presence of earwigs inside the structure is normally the result of a few earwigs seeking food, moisture or shelter in response to changing conditions outdoors. A simple, properly applied treatment of the structure’s exterior will generally solve minor earwig problems. A wettable powder or microencapsulated insecticide should be used. Rocks, logs, and thick layers of mulch should be lifted or raked back to allow the treatment of areas where earwigs are most likely to be living.

Under proper conditions, large populations may develop near a structure and begin entering the structure on a frequent basis. It is these situations which call for a more integrated control effort. The long-term control of large populations of earwigs around a particular structure begins with a careful inspection of the exterior. All areas where earwigs are living on the property must be noted.

Insecticide applications alone will only provide relief for a short period of time. Correction of conditions contributing to the development of large populations of earwigs must be accomplished. This usually involves removing harborages such as firewood, leaf litter, thick layers of mulch and piles of bricks. Landscape timbers, storage sheds and dead tree limbs also serve as reservoirs from which earwigs reinfest the structure. A flushing agent, such as pyrethrum, is a handy aid in finding the areas where earwigs are living.

Thick layers of mulch must be raked back from the foundation. The customer should be instructed to reduce mulch layers to a minimum of 2 inches. All vegetation, except grass, should be cut back at least 12 inches from the foundation. This is particularly true for ground covers such as ivy.

Firewood should be stored as far from the structure as possible and then stored off the ground. Dead limbs and stumps should be removed, as well as piles of leaf litter. Piles of bricks, boards and other debris must be removed. As many exterior cracks as possible should be caulked or sealed. Most of these measures, of course, will need to be done by the customer. The service technician needs to point out these items to the customer and provide any recommendations in writing. If these non-chemical control measures are not enacted, the earwig problem will most likely continue despite repeated insecticide applications.

Once the harborages around the structure have been removed and other contributing conditions corrected, a thorough exterior treatment can be performed. Exterior cracks should be treated with a residual dust insecticide before they are sealed, otherwise earwigs hiding in the cracks may be trapped and forced to find their way into the structure.

The service technician should not simply treat the foundation of the structure and leave. All areas where earwigs were found and identified during the inspection, must be treated. This involves turning over rocks and landscape timbers, where possible, to expose the areas where earwigs are living. This includes the entire property! Mulch in landscape beds will need to be treated, raked back and treated again to achieve thorough penetration. The areas under decks also may need to be treated.

Treatment of the mulch and foundation is best accomplished using a power sprayer unit, although a backpack sprayer or a compressed air sprayer can be used (it will just take longer.)

The key is to reduce the numbers of earwigs on the property to as low a level as possible. This greatly reduces the chances earwigs could enter the structure.

INDOOR CONTROL. Populations of earwigs are generally highest in mid-to late summer. This is usually when problems inside structures generally occur. Once indoors, earwigs prefer to hide in moist, dark areas. They are common in bathrooms, utility rooms and kitchens. Earwigs will hide in drawers, clothing and beds. Needless to say, this can cause homeowners much dismay.

Control of earwigs indoors begins with an inspection. Use of a flushing agent is a big help. Cracks and crevices where earwigs are found should be treated using a residual aerosol or dust insecticide. The floor/wall juncture in unfinished areas such as basements and garages can be spot-treated using a wettable powder or microencapsulated insecticide. Treatment of earwigs indoors is not unlike treating a brown-banded cockroach infestation, only not quite as intensive.

The control of earwigs is not difficult if the service technician performs a thorough inspection and bases his treatments on what he uncovers during the inspection.

Stoy Hedges, a Registered Professional Entomologist, is a frequent contributor to PCT.