Utah Pests News Fall 2007

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European Earwigs Can Be a Problematic Garden and Nuisance Pest

 
 

Earwig damage to peach

 
 

Earwig damage to cherry

 

 

Earwigs captured in bacon grease

If you look up the feeding habits of the European earwig (Forficula auricularia) in a reference book, it will state that it primarily feeds on decaying organic matter. Well, this isn’t true for Utah and probably for many arid regions. It is true that the European earwig is omnivorous (feeds on multiple food types), including its predaceous habits, but the injury they cause to seedlings, tender shoots, flowers, and ripe fruits far outweighs their benefits.

A lengthy drought beginning in the late 1990s appears to have increased earwig damage and exacerbated plant stress problems in the Intermountain Region. For example, the severity and distribution of earwig injury in northern and central Utah has increased in the last 5-10 years. The drought has likely reduced the volume of organic matter available for detritivores such as earwigs and driven them to feed more on living plant material. However, even in situations with adequate detritus, earwigs continue to feed on garden plants. They seem to have adapted to the herbivorous life style. An increasing number of landscape managers and home gardeners are searching for solutions to earwig problems.

The European earwig is an exotic introduction to North America. There are several species of native earwigs in the West, and these are not plant pests. Earwigs are easy to recognize by their large pincer-like appendages on their hind ends, called cerci. The cerci are used in self-defense and courtship and will only deliver a mild pinch at most to humans. Their body is elongated, flat, and red-brown in color. They are ¼ -1¼ inches in length. Adults have a short pair of leathery wings covering a folded pair of membranous wings. They are weak fliers and mostly move about by crawling.

Earwigs can emit a foul-smelling, yellow-brown liquid from their scent glands. They are omnivorous and will scavenge on dead insects and decayed organic matter, prey on live insects, and chew on living plant material. Earwigs get their name from an old superstition that they would crawl into the ears of sleeping people and bore into the brain. This belief is not true.

A wide range of plants are hosts for the European earwig including annual flowers (especially marigolds, dahlias, zinnias, and hollyhocks), herbs (especially basil and dill), vegetables (especially lettuce, spinach, Swiss chard, cole crops, beets, sweet corn silks, beans, and carrots), roses, caneberries, apricots, peaches, shrubs, and small trees. When earwig populations are high, injury can be especially severe on tender leaves and shoots, flower petals, and ripe fruits. Earwigs are nocturnal. If ragged chewing injury on plants is observed, but no culprit can be found during the day; check the plants at night with a flashlight for the presence of earwigs.

Because earwigs are also beneficial due to their predaceous and decomposer feeding habits, populations should only be suppressed when they are causing harm. Begin in the spring and early summer by locating "nests" of females brooding their young. These earwig congregations occur in soil under stones, boards, mulch, compost piles, and other debris. Target control efforts on nests and on plants when injury first appears.

Reduce refuges where they can hide during the day such as debris, groundcovers, and larger pieces of mulch. Place traps in the evening and remove earwigs in the morning. Effective traps include shallow cans baited with vegetable or other odorous oils, moist rolled newspaper, cardboard boxes baited with oatmeal or bran and with pencil-sized holes near the bottom, hollow bamboo canes, and sections of garden hose. To prevent earwigs from climbing into trees, shrubs and other plants, apply a band of sticky adhesive such as Tangletrap® around the trunk or stem.

Insecticides can also help suppress earwigs. Select an effective product and apply it in the evening just before earwigs will be most active. Recommended conventional insecticides include permethrin, esfenvalerate, bifenthrin, carbaryl, and malathion. Effective organically-certified insecticides include azadirachtin, pyrethrum, and diatomaceous earth. Use enough water in the application to cover the plants or to carry the chemical into the top layer of soil or mulch where the earwigs are hiding. Immature earwigs are more susceptible to insecticides than adults so make applications early in the season. Adults have a thick, hard exoskeleton that is difficult to penetrate. Not all insecticide products are registered on edible plants. Be sure to fully read the product label before making an application.

To reduce the entry of earwigs into buildings, create a clean, dry border using gravel or stone immediately around the foundation wall; eliminate refuges near the foundation such as groundcovers, climbing vines, weeds, thick mulches and vegetation, and piles of debris, leaves, or wood; seal cracks and crevices around windows, doors and utility cable holes in walls; apply insecticides (see recommended products above) around the foundation and flower beds or turf within several yards of the home.

-Diane Alston, Extension Entomologist