Identification & Control of Earwigs
Eliminating this commonly encountered occasional invader from a structure requires a range of nonchemical control measures followed by the application of insecticides to specific active harborage sites.
Editor’s Note: In this excerpt from the 10th Edition of the Mallis Handbook of Pest Control, which will be published later this year, one of the industry’s leading entomologists provides practical insights about how to identify and control a common occasional invader — earwigs.
Many of us have asked the question, “What makes something an occasional invader?” If we define the term, “occasional invader” would literally be something that a client does not want to see that would appear infrequently. Whether or not it is a pest comes down to the definition. If we define “pest” as an annoying or troublesome animal or thing, then an occasional invader pest would be some type of animal — including an insect or arthropod — that appears randomly in their home or business. Any person working in the pest management industry for any length of time will encounter some pest that falls into this group. Such occasional pests can pose a difficult challenge to solve.
It should be noted that although the occasional insect may appear to be a “minor” pest to the pest management professional, it can be a “major” pest to the client. Moreover, what is a common pest in one region of the country may be a rare or introduced pest in another area. In the following article we’ll examine one of the more common occasional invaders encountered by pest management professionals, earwigs.
Fact vs. Fiction
Earwigs owe their name to the widespread superstition that they purposely crawl into the ears of sleeping people and bore into the brain. According to Fulton (1924), the word “earwig” is derived from the Anglo-Saxon “earwicga,” meaning “ear creature.” 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 forcep-like cerci extending from the abdomen.
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 typically much straighter when compared with the strongly curved cerci of the male.
Earwigs are brownish to black in color, narrow-bodied, elongate, and somewhat flattened insects, ranging 1/4 inch to 1 inch (7 to 25 mm) in length. Adults may be winged or wingless, and they have chewing mouthparts. The nymphs add antennal segments at each molt until reaching a total of 10 segments as an adult. The wings, when present, barely extend onto the abdomen, with the tips of the folded membranous hind wings extending from under the forewings. Upon cursory glance, earwigs may resemble rove beetles. Approximately 2,000 worldwide species of earwigs have been described, most occurring in tropical regions (Arnett 2000). Twenty two species are found in the U.S. (Borror et al. 2005).
Over the past several decades, relatively little research has been conducted on life histories of the North American earwig species. 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. According to Eisner (1960), the European earwig, Forficula auricularia Linnaeus, uses its cerci as a first line of defense and the secretions as its secondary defensive tactic.
Earwigs are active at night and hide during the day. Being thigmotropic, earwigs, like cockroaches, 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 on aphids and larger insects such as flies, captured with their pincer-like cerci.
Earwigs are well known for their gregarious behavior, which, similar to cockroaches, is driven by an aggregation pheromone (Sauphanor 1992; Walker et al. 1993). At least, in the European earwig, the aggregation behavior appears to be associated with contact between conspecific individuals and frass, resulting in aggregations of several dozen to several hundred individuals (Walker et al. 1993). According to Sauphanor (1992), the aggregation pheromone is active in controlling the aggregation behavior of all nymphal instars, as well as the adults of both sexes.
Maternal care is also 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 their mates. Throughout the development of the embryo, the female picks up each egg individually in her mouth and “licks” them. The function of this “licking” behavior is still unknown. It has been speculated that licking may prevent the growth of fungus on the surface of the egg. Shepard et al. (1973) stated that eggs not regularly cared for by the female are destroyed by fungal infections unless treated with a fungicide. Upon hatching, the young nymphs remain in the earthen chamber throughout the first instar and are provided with food gathered by the female (Vancassel 1977).
European earwig adults are 5/8 inch (16 mm) long, dark reddish-brown in color with a reddish head, and characterized by pale, yellowish-brown legs. Adult males have strikingly different-sized forms (polymorphs) that have forceps of varying lengths and complexity of form with some individuals measuring up to 3/16 inch (5 mm) long. The female’s cerci are slender and straight and have a slight inward curve toward the tip.
This cosmopolitan insect is believed to have been first observed in the United States in 1907 in Seattle, but it is now found throughout much of the United States and parts of Canada. Because large numbers commonly seek shelter inside and around building exteriors and homes, the European earwig often becomes a household pest. This earwig is an omnivorous feeder, very fond of plants as food.
Because this earwig feeds on a variety of plants, however, the injury it causes to any particular plant is usually not serious. Dimick and Mote (1934), upon examining the insects’ digestive tracts, found the contents to be largely lichen and pollen. When these insects feed on plants, they make small irregular holes in the leaves and may even skeletonize them. If it were not for an absence of slime, their work could be mistaken for that of slugs.
The European earwig is disseminated largely through people’s activities. In this respect, Crumb et al. (1941) noted this earwig “may be carried long distances in bundles of newspaper, the luggage of travelers, cut flowers, packages, and crates of merchandise, lumber and shingles, automobiles and even rarely in letters.” The earwig readily avails itself of any dark, moist crevice, such as those found in balled plants, heaps of manure, boards and similar locations. Morgan (1926) noted that the adults will float in water for 24 hours and then may resume immediate activity upon reaching a dry surface. It is in this way they are distributed on debris floating in streams and rivers. For a few decades following its North American introduction, population explosions of the European earwig were common. In more recent times, populations of this earwig have stabilized in most of its geographical range and only occur in large populations when environmental conditions are favorable.
Fulton (1924) and Crumb et al. (1941) studied the life history of the European earwig in Oregon, while Lamb and Wellington (1974, 1975) and Lamb (1976) reported on the life history of this earwig in British Columbia. These authors reported that the adults are more commonly seen during the cooler months and hide beneath boards, stones and similar ground cover 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. Most females will produce two broods, the first containing 30 to 55 eggs, although only one generation occurs in North America. First brood eggs hatch in slightly more than 70 days during the cool spring temperatures, but eggs laid during warmer months take about 20 days to hatch.
The female European earwig is well known for her maternal care for the young. The mother frequently moves the eggs from one part of the cell to the other, rolling and cleaning them in her mouth. After hatching, the nymphs go through two phases during growth — nesting and free-foraging. After the first molt, the female opens the nest and the more venturesome second instar nymphs seek food at night but return to their nest during the day. The third and fourth nymphal instars leave the nest and begin a free-foraging existence on the soil surface. By mid- to late-June, most of the first brood has left the nests and many females lay a second batch of eggs. By August and September, both broods have reached adulthood and pairing begins.
A great deal of the management efforts directed at earwig infestations involve nonchemical means followed by the application of insecticides to specific active harborages. If the conditions supporting the infestation are not addressed, complete relief from the infestation is not likely to be realized.
• Physical Removal. In larger infestations, vacuums are useful for removing large numbers of earwigs found in harborages outdoors as well as 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.
• Harborage Removal. Unfortunately, the habitat that is created and is desired by suburbanites featuring landscaping, mulches, ornamental rocks, patio stones, picnic furniture, decks, etc., is also conducive to earwig populations. The elimination of outdoor harborages used by earwigs, such as piles of lumber, bricks and other items, is a key to long-term control. Elimination of heavy ground covering vegetation near buildings is recommended. Tree and shrub limbs should be trimmed away from walls and the roof. Gutters need to be kept clear of leaves and other debris.
• Excess Moisture. Moisture management is also highly important. Good drainage and grading and proper direction of irrigation sprinklers minimizes moisture beside the foundation. Early morning watering allows the vegetation to dry during the day rather than remain wet throughout the night. Crawlspaces also may need vapor barriers, fans or sump pumps to sufficiently reduce high humidity and water.
• Modification of Exterior Lighting. The striped earwig and sometimes the European earwig, will be attracted to exterior lights, so the use of sodium exterior lights or yellow “bug light” bulbs 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 of cracks and crevices and the installation of weather stripping around windows and doors. Foundation and attic vents should be equipped with tight-fitting insect screens.
• Traps. Traps made of bamboo or rolled cardboard or 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. Grooved board traps set in shrubbery, hedges, and around trees, as described by Morris (1965), have been used to effectively reduce European earwig populations. Sticky monitoring traps can also be used to detect and monitor the distribution of earwigs inside.
• Treatments. The application of insecticides to control earwigs generally should be undertaken after or in combination with addressing the conditions contributing to the infestation. The best results are achieved when treatments are directed at active harborages discovered during the inspection.
Historically, baits used around the exterior of structures have played a major 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. Residual water-based formulations (e.g., WP, SC, CS) are the most appropriate formulations for perimeter treatments, as well as to 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 sealing these openings following treatment is recommended. Use caution when sealing any openings to the structure. Some openings such as weep holes are needed to maintain the health of the structure itself. Special attention should be paid to the areas most frequented by earwigs. In addition to building foundations, piles of wood and stones, wooden fences, tree holes, the underside of decks, sheds, landscape timbers, and dog houses are likely harborages. The European earwig’s preference for cracks inside and out is similar to that of the German cockroach indoors; therefore, crack and crevice treatments are the primary treatment technique to employ. In many homes mulch beds are a typical source for this insect. When treating mulch beds for earwigs, it is often necessary to remove the mulch and treat the soil directly.
Frank Meek is international technical and training director for Orkin.