Forficula auricularia is a species complex comprising the common earwig. It is also known as the European earwig. It is an omnivorous insect belonging to the family Forficulidae. The name earwig comes from the appearance of the hindwings, which are unique in their resemblance to human ears when unfolded. The species name of the common earwig, auricularia, is a specific reference to this feature. The European earwig survives in a variety of environments. It is also a common household insect in North America. They are often considered a household pest because of their tendency to invade crevices in homes and consume pantry foods, though they may also act as beneficial species depending on the circumstances.
Forficula auricularia is reddish-brown in color with a flattened elongated body and slender beaded antennae. Earwigs possess pairs of pincers or forceps at the tip of the flexible abdomen. Both sexes have these pincers. In males, they are large and curved, whereas in females, they are straight. Nymphs are similar to adults in appearance, though their wings are either absent or small.
Morphology Forficula auricularia have elongated flattened brownish-colored bodies, with a shield-shaped pronotum, two pairs of wings, and a pair of forceps-like cerci. They are about long. The second tarsal segment, which is located on the leg, is lobed, extending distally below the third tarsal segment. The antenna consists of 11–14 segments, and the mouth parts are of the chewing type.
An anatomical diagram of the common earwig can be found to the right. Section A represents the head, B represents the thorax, and C represents the abdomen. The numbers correspond to different body parts. 1 is pointing to the pronotum (a plate-like structure that covers the thorax), and 2 is pointing to the elytra (tough outer wings used to protect the more delicate hind wings). 3 is pointing to the delicate hind wings peeking out, and 4 is pointing to the abdomen. 5 is pointing to the cerci (paired appendages on the abdomen of many insects).
Taxonomy
A detailed analysis of mitochondrial DNA from specimens across Europe has established that Forficula auricularia is a complex of several morphologically indistinguishable species. There are at least four species in the Forficula auricularia complex: Forficula auricularia, Forficula dentata, Forficula mediterranea, and Forficula aeolica.
The name Forficula auricularia applies to those found in Scandinavia and Central Europe, whereas Forficula dentata is the usual species found in the British Isles and Western Europe. There are several other members of the complex distinguished based on mitochondrial haplotypes. In North America, European earwigs were found to comprise two sibling species, which are reproductively isolated.Wirth T., et al. (1998). Molecular and reproductive characterization of sibling species in the European earwig (Forficula auricularia). Evolution 52(1) 260–65. Populations in cold continental climates mostly have one clutch per year, forming Forficula auricularia whereas those in warmer climates have two clutches per year, forming Forficula dentata.
Distribution Originating in Europe, western Asia and possibly North Africa, Forficula auricularia was introduced to North America in the early twentieth century and has since spread throughout much of the continent. It was accidentally introduced into New Zealand by Early European settlers. European earwigs are most commonly found in temperate climates, since they were originally discovered in the Palearctic region, and are most active when the daily temperature has minimal fluctuation.Capinera, J. 2001. Handbook of Vegetable Pests. Academic Press, San Diego, CA.
Habitat Thriving in cool, moist habitats, European earwigs exhibit optimal growth at a mean temperature of . Their daily abundance in a given year has been linked to factors such as temperature, wind velocity, and the prevalence of easterly winds. The development of European earwigs also depends on temperature. The occurrence of European earwigs can be predicted based on weather parameters. Hibernating adults can tolerate cool temperatures, but their survival is reduced in poorly drained soils such as clay. To avoid excessive moisture, they seek the southern side of well-drained slopes. Sometimes they also occupy the hollow stems of flowers where the soil is poorly drained. Their eggs are capable of resisting damage from cold and heat.
Behavior European earwigs spend the daytime in cool, dark, inaccessible places, such as flowers, fruits, and wood crevices. They are primarily active at night, seeking out food ranging from plant matter to small insects. Though they are omnivorous, they are considered as scavengers rather than predators. Often they consume plant matter, though they have also been known to feed on aphids, spiders, insect eggs, and dead plants and insects, among other things. Their favorite plants include the common crucifer Sisymbrium officinale, the white clover Trifolium repens, and the dahlia Dahlia variabilis. They also like to feed on molasses, as well as on nonvascular plants, lichens and algae. They prefer meat or sugar to natural plant material even though plants are a major natural food source. European earwigs prefer aphids to plant material such as leaves and fruit slices of apple, cherry and pear. Adults eat more insects than do nymphs.
Although Forficula auricularia have well-developed wings, they are fairly weak and are rarely, if ever, used. Instead, as their main form of transportation, earwigs are carried from one place to another on clothing or commercial products like lumber, ornamental shrubs and even newspaper bundles.
Reproduction
Courtship
Courtship in European common earwigs is unique in the sense that both males and females take active roles in courtship. Unlike most earwig species, detailed observations of the courtship and mating processes in Forficula auricularia reveal complex sexual behaviors for both the males and females. The European earwig possesses sexually dimorphic cerci (forceps). Adult males are polymorphic in body weight and head width, as well as cercus length and width. The males have large, heavy, curved forceps that are very robust and broadened basally with crenulate teeth. Females have straight and slender forceps that are 3 mm long, and are less robust and straighter. Studies have demonstrated the significance of these cerci for use as displays in early courtship and as a tactile stimulus for the female during copulation, as well as feeding and self-defense purposes.
Early courtship typically consists of male displays in which they wave or bob the cerci. The common earwigs do not have a sex pheromone because they already have an aggregation pheromone which already brings the male and female insects into close proximity with one another.
Courtship will then progress to tactile stimulation by the males and sometimes females, if they are receptive. The males tend to use their cerci to stroke and encircle the female's body. Both sexes participate in waving, bobbing, and stroking movements, but only males use their forceps to encircle the female. It is interesting to note that the cerci seem to be strictly used for courtship/stimulation and defense against any potential threats; the males do not ever use the forceps aggressively as claspers to hold the female in place during copulation.
The cerci stimulation is followed by abdomen arching, bobbing, and twisting before copulation occurs. Research suggests that male cerci are necessary for reproductive success because of their role as either secondary sexual characteristics for courtship or as weapons in altercations; males with their cerci removed were unable to successfully find a mate.
Copulation A male finds prospective mates by olfaction. After a complex courtship performance by both the male and female, the male slips his cerci under the tip of the female's abdomen so that his and her ventral abdominal surfaces are in contact with each other, while both face in opposite directions. If not disturbed, pairs can stay in this mating position for many hours. During copulation, the females often move around and feed. Because they provide brood care, female Forficula auricularia have intensive nutritional requirements which likely motivates their activity during copulation—especially because female European earwigs rarely ever feed during oviposition (laying of the eggs), incubation, and brood care. Matings occurred frequently among clustered individuals particularly in locations that allow both partners to cling to a surface. Under laboratory conditions, the mating season peaked during August and September, and a single mating event enabled females to lay fertilized eggs.
Maternal care European earwig nymphs look very similar to their adult counterparts except that they are a lighter color. The young go through four nymphal stages and do not leave the nest until after the first moult.
European earwigs overwinter about below the surface of the ground. The female earwig lays a clutch of about 50 eggs in an underground nest in the autumn. She enters a dormant state and stays in the nest with the eggs.
Common earwigs exhibit varying levels of maternal care. Female earwigs typically show maternal care through behaviors such as guarding and tending to their eggs and nymphs. The female cares for her young by shifting the eggs about and continuously cleaning them with her mouth and forceps to avoid fungal growth and pathogens through careful extraction of fungal spores from the eggs. She protects the eggs by staying close to the nest, fiercely defending against predators, applying chemical protection against desiccation through egg grooming, and relocating the entire clutch under stressful conditions. Their protection of the eggs involves remaining close to the nest and defending against potential predators.
In the spring, she spreads them out into a single layer and the young emerge from the eggs. After the eggs hatch in the spring, the mother continues to care for the nymphs, providing protection, grooming, food, and sometimes even regulating the temperature in the nest. The mother provides food from the larval stage to the first instar (term for a developmental stage in insects) and will continue to defend the aggregated family group in the burrow and on nocturnal foraging excursions. She guards them until they reach maturity after about one month. It is possible for the female to lay a second brood in one season and by the end of August all of the young reach maturity.
Life cycle
European common earwigs can produce either one or two broods per year. Females and males often hibernate together in pairs in underground nests. Females oviposit, or lay, their eggs at the end of winter/ beginning of spring and then expel the male from the nest. These eggs are pale yellow or cream colored and have an elliptical shape.
The mother incubates and cares for the eggs until they hatch. After hatching, the nymphs go through four nymphal instars before reaching maturity and adulthood.
There are two distinct phases of the common earwig's life: the nesting phase and the free-foraging phase. In the nesting phase, family units consist of the male and female pair and then just the female and her nymphs. They may leave the nest at night for foraging excursions, but the mother and her nymphs return to the nest and stay there during the daytime. In the free-foraging phase, different family units will interact, and the nymphs no longer return to their nests after foraging. Instead, they go on long foraging excursions and shelter in trees and crevices. At this point, females may produce a second brood since they have finished raising and tending to the first brood.
Selfish vs. altruistic behavior