Forficula auricularia

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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,

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.

The name Forficula auriculata 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. Populations in cold continental climates mostly have one clutch per year, forming Forficula auriculata 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.

Habitat

Thriving in cool, moist habitats, European earwigs exhibit optimal growth at a mean temperature of . The development of European earwigs also depends on temperature. Hibernating adults can tolerate cool temperatures, but their survival is reduced in poorly drained soils such as clay. 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. They also like to feed on molasses, as well as on nonvascular plants, lichens and algae. 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.

Reproduction

Courtship

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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.

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.

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.

thumb|310x310px|Female and nymphs

One explicit form of altruistic behavior in common earwigs is the fact that females do not reject foreign offspring or eggs and will exhibit the same level of care to foreign eggs as her own eggs. In many species, kin bias prevents parents from investing care and energy into any foreign offspring in order to allow them to more effectively invest in their own offspring thus ensuring that their own genes are passed on. Common earwig mothers, however, will not eliminate foreign eggs and will actually groom, defend, and provide for them to the same extent at which she cares for her own eggs. A likely explanation would be that common earwig mothers simply cannot differentiate between their own eggs and foreign eggs, but this is not the case. Common earwig mothers immediately and regularly apply a bouquet of cuticular hydrocarbons to the surface of their eggs. This bouquet is family specific and allows for differentiation between the mother's own eggs and foreign eggs. This phenomenon indicates that there is limited selection pressures promoting female common earwigs to reject foreign eggs which allows them to display the altruistic behavior of caring for foreign offspring.

Scientists believe that common earwigs produce this aggregation pheromone in their tibial glands, cuticular lipids, or fecal matter. Males, females, and nymphs all exhibit strong responses to the aggregation pheromone. However, there is mounting evidence that the aggregation pheromones are stage-specific meaning depending on the chemical contents of the particular pheromone, it will be more likely to attract either nymphs or adults. Benzoquinones are a component of the aggregation pheromone that attracts adult common earwigs. The same was not true for nymph-stage common earwigs which responded well to experimental aggregation pheromones with and without the benzoquinones.

Agricultural impact

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Forficula auricularia has been known to cause significant damage to crops, flowers, and fruit orchards when at high population levels. Some of the commercially valuable vegetables it feeds upon include cabbage, cauliflower, chard, celery, lettuce, potato, beet, and cucumber among others. Earwigs readily consume corn (maize) silk and can damage the crop. Among fruits, they have been found to damage apple and pear orchards. On apple trees specifically, Forficula auricularia feed on the fruit (primarily on parts where the fruit is already rotting or cracked) and contaminate the fruit with frass (powdery wood debris that is the result of insect foraging/ boring). They damage young plum and peach trees in early spring when other food is scarce by devouring blossoms and leaves at night. They are often found wedged among petals of fresh cut carnations, roses, dahlia and zinnia. The tachinid flies Triarthria setipennis (Fallen) and Ocytata pallipes were introduced in North America to control Forficula auricularia in the 1920s.

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Insecticides have also been successfully implemented, although commercial products are rarely targeted specifically towards earwigs. Multipurpose insecticides for control of earwigs, grasshoppers, sowbugs and other insects are more common.

Humans have, however, found beneficial uses of Forficula auricularia in the pest management of other insects. The European common earwig is an omnivore and is also referred to as a generalist predator or scavenger meaning they have many different forms of prey and will feed on whichever prey species is most available. The European earwig is a natural predator of a number of other agricultural pests, including the pear psyllid and several aphid species, and in this regard has been used to control outbreaks of such organisms. The common earwig is an important predator of many different orchard/ crop pests such as the wooly apple aphid (Eriosoma lanigerum) which is one of the most problematic pests in apple orchards. Research has repeatedly shown that low numbers of common earwigs are associated with wooly apple aphid infestations whereas high numbers of common earwigs lead to decreased aphid populations in orchards so much so that farmers sometimes do not even need to use chemicals or pesticides. Therefore, despite their potential adverse effects on some crops, European common earwigs play a crucial role in managing wooly aphid apple populations in apple orchards.

References

External links

ARKive: Images of Life on Earth - Forficula auricularia fact page as well as photos and video
Encyclopedia of Life - Forficula auricularia images and facts
Royal Horticultural Society- Gardening advice: Earwigs - Gardening advice in relation to Forficula auricularia