Earwigs

The presence of forcep-like cerci is the key character distinguishing earwigs from other groups of insects. The cerci are used by the earwig as both defensive and offensive weapons.

Editor's note: This is the first in a series of excerpts from the soon-to-be-published Eighth Edition of The Handbook of Pest Control. The following information has been revised and updated by Richard Cooper, a contributing editor to the book, and vice-president of technical services for Cooper Pest Control, Lawrenceville, N.J. Throughout the coming year, PCT magazine will publish monthly excerpts of The Handbook of Pest Control.

Earwigs owe their name to the widespread superstition that they purposely crawl into the ears of sleeping persons and bore into the brain. Despite the unusual folklore that surrounds this insect, translations of the Latin names Dermaptera (order) and Forficulina (suborder) more accurately describe the morphology of this insect. Dermaptera refers to the "skin-like" forewings present in winged species, and Forficulina translates to "little scissors," referring to the prominent abdominal cerci.

Approximately 1,100 worldwide species of earwigs have been described, but only 22 species are known to exist in the United States. Fortunately, only a few species are household pests.

IDENTIFICATION. Earwigs are brownish to black in color, narrow bodied, elongate and somewhat flattened insects, ranging from 1/4 inch to 1 inch in length. They have chewing mouthparts, and the tarsus of each leg has three segments. The antennae of the adults have 10 segments. The nymphs have fewer antennal segments, with additional segments being added at each molt. Adults may be winged or winged or wingless. When wings are present they barely extend onto the abdomen and resemble the wings of the rove beetle.

The presence of forcep-like cerci is the key character distinguishing earwigs from other groups of insects. The cerci are used by the earwig as both defensive and offensive weapons, and occasionally are used to capture prey. Additionally, the morphology of the cerci is quite variable and may be used as an aid in distinguishing between species as well as sexes. The cerci of females are much straighter when compared to the strongly curved cerci of the male.

BIOLOGY. Earwigs undergo gradual metamorphosis, and most species overwinter in the adult form. Some species have glands from which they squirt a foul-smelling, yellowish-brown liquid for defensive purposes.

Earwigs are active at night and hide during the day. Being thigmatrophic, earwigs prefer to hide or rest in dark, moist cracks, such as those found under tree bark and beneath stones, boards, and debris.

The diet of earwigs is diverse and consists of a wide variety of plant and animal matter. Earwigs feed on leaves, flowers, fruits, and fungi, as well as aphids and larger insects, such as flies, captured with their pincer-like cerci.

Maternal care is readily exhibited among earwigs. Females dig a burrow or earthen cell into which they deposit approximately 20 to 60 eggs. Once this is complete, the females gather the eggs and organize them into a pile. The female tends to the eggs and guards the "nest" from all intruders, including her mate.

AN IPM APPROACH. A great deal of the management efforts directed at earwig infestations involves nonchemical means followed by the application of insecticides to specific active harborages. If conditions supporting the infestation are not addressed, complete relief from the infestation is not likely to be realized.

Physical Removal of Earwigs. A vacuum device can be used to remove the occasional earwig found indoors. In larger infestations, vacuums are also useful for removing large numbers of earwigs found in harborages outdoors and indoors. If items stored outside are infested with earwigs, these items may be shaken to dislodge the insects, which can then be removed by vacuuming. If populations exceed an individual's tolerance threshold, the measures listed below may be implemented to reduce earwig populations and entry into the structure.

Harborage Removal. The habitat that is created and is desired by suburbanites featuring landscaping, mulches, ornamental rocks, patio stones, picnic furniture, decks, etc., unfortunately is also conducive to earwig populations. The elimination of outdoor harborages used by earwigs is a key to long-term control. Alteration of other conditions contributing to an infestation is also important.

Conditions which should be addressed include:

   1) Remove debris and organic matter within a zone of at least 3 feet of the structure. Eliminate piles of lumber, bricks, leaf litter, and firewood off the ground and as far from the structure as possible.

   2) Establish an 18- to 24-inch vegetation-free zone around the perimeter of the structure using gravel or landscaping stone, underlined with landscape cloth.

   3) Trim back tree limbs that heavily shade the home and contribute to moisture retention on and around the structure.

   4) Repair or relocate broken or poorly placed rain downspouts and irrigation systems that contribute to moist areas that are attractive to nesting female earwigs.

   5) Grade property to insure that water drains away from the structure.

   6) Close mowing and edging of the lawn, especially near the foundation, makes a lawn less attractive to earwigs.

   7) Early morning watering allows the vegetation to dry during the day rather than remain wet throughout the night.

   8) Ventilate crawlspaces to remove moisture. Vents should be located every 25 feet and at least 6 inches above grade. Vents should also be free and clear of vegetation that will obstruct air flow.

Modification of Exterior Lighting. The striped earwig, and sometimes the European earwig (see related story), will be attracted to exterior lights so the use of sodium exterior lights or yellow "bug lights" on the outside of buildings will greatly reduce the numbers of these earwigs attracted to a structure.

Exclusion. Access into the structure can be reduced by caulking cracks and crevices and by the installation of weather-stripping around windows and doors.

Traps. Traps made of bamboo or rolled newspaper take advantage of the earwig's propensity to crawl into cracks and crevices. Traps should be placed out prior to dark and checked the following morning. Earwigs that are trapped can be shaken into a pail of soapy water. Traps can also be used to monitor the distribution of earwigs in an effort to determine where control efforts should be focused.

USE OF INSECTICIDES. The application of insecticides to control earwigs generally should be undertaken only after addressing the conditions contributing to the infestation and a thorough inspection to determine the harborages used by earwigs in and around the structure. At the very least, the removal of outdoor harborages should be completed, including:

Historically, baits used around the exterior of structures have played a large role in the control of earwigs. Today, few effective baits are available that are labeled for such use. As a result, control of earwigs using insecticides is largely accomplished through the use of perimeter treatments. A wide variety of current insecticides list earwigs on the label, both for interior and exterior use. Wettable powder or microencapsulated insecticides are the most appropriate formulations for perimeter treatments, as well as earwig harborages outdoors. Dust formulations should be used to treat inside cracks, holes, and voids in the building's exterior where earwigs may be hiding, and these openings then caulked following treatment. When treating turf or plants around a building, do not make applications exposed to the hot sun to avoid phytotoxicity to those plants. Good exterior/perimeter control of earwigs also has been obtained with granular insecticides containing 2.5% to 5% active ingredient.

Whether using sprays, baits, or granules, special attention should be paid to the areas most frequented by earwigs, so the initial inspection is critical to success in controlling earwigs. In addition to building foundations, this includes areas along fences and walks, around trees and utility poles, and around wood piles and rocks. Wooden fences with their numerous cracks are especially preferred by the European earwig. When controlling the European earwig, crack and crevice treatments are the primary treatment technique to employ. This earwig's preference for cracks outside is similar to that of the German cockroach inside.

For severe infestations resulting in heavy invasions, it may be necessary to treat much wider outdoor areas. This can be achieved using products labeled for whole yard treatment. Such measures may be particularly appropriate in the fall when more earwigs may seek shelter indoors.

In general, indoor treatments are only supplemental to outdoor control measures. Many residual insecticides labeled for outdoor applications include directions for use indoors.

Sidebar: Common Pest Species

The earwigs most commonly encountered by pest management professionals include the European earwig, ring-legged earwig, and striped earwig. A brief review of each follows:

European Earwig. European earwig adults are 5/8 inch long, are dark reddish-brown in color with a reddish head, and have pale, yellowish-brown legs. Adult males have strikingly different-sized forms (polymorphs) which have forceps of varying lengths and complexity of form. Some individuals have forceps approximately 3/16 inch long, while others have forceps 3/8 inch long. The female's cerci are slender and straight and have a slight inward curve toward the tip.

Because large numbers commonly seek shelter inside and around buildings, the European earwig often becomes a household pest. European earwig adults are more commonly seen during the cooler months and hide during the day. The adults mate in late summer and early fall before establishing subterranean nests. Before the female oviposits, she drives out her mate. These males return to the surface and are commonly seen from mid-February into April.

Ring-Legged Earwig. The ring-legged earwig occurs throughout the United States, but it is most common in the South and Southwest. This insect has habits similar to that of the European earwig, feeding on both plants and other insects.

The adults may reach a length of 1 inch. They vary from brown to black in color, with a yellowish-brown undersurface. The femur and tibia of the yellowish legs are ringed with brown stripes. The antennae are 16- to 18- segmented, dark brown in color, and the third, fourth, and sometimes the fifth segment from the abdominal apex are yellow to white. This insect is nocturnal, avoids light, and is an omnivorous feeder.

Striped Earwig. The striped earwig is also commonly called the shore or riparian earwig. The adults are usually larger than the European earwig, measuring about 1 inch long. Their color varies from pale brown to chestnut or reddish-brown, with black markings, and the abdomen is usually banded. The most distinguishing marks are two dark bands running the length of the pronotum behind the head.

The striped earwig can be found in tropical and subtropical areas worldwide. The species was first reported in Texas and is now found from California through Arizona and the Gulf Coast states north to North Carolina. It generally lives in a burrow beneath debris and thatches. This earwig has not been known to damage plants, but commonly seeks shelter in buildings. This species is also attracted to lights at night and has an odor if disturbed.