Family Forficulidae

Forficula auricularia L. Common earwig

Earwigs are polyphagous insects, and often cause damage to chrysanthemum, clematis, dahlia and other herbaceous plants, including potato. Damaged petals become ragged, spoiling the appearance of ornamentals. Attacks on leaves are unimportant but chewed buds may die, resulting in blind shoots; most damage occurs from June to September. Earwigs sometimes attack celery plants, to form brownish, longitudinal grooves in the petioles; such damage is distinguished from similar symptoms of physiological disorders by the presence of masses of black frass (Plate la) and tends to occur most frequently on plants suffering from boron deficiency. Earwigs may also shelter beneath the sheaths of developing maize (and sweet corn) cobs and then damage the kernels, particularly at the tips of the cobs (Plate lb). In orchards, earwigs often feed on ripening fruits already damaged by mechanical or other means; also, in black currant plantations, earwigs (which often rest in the bushes) are frequent contaminants in trays of mechanically harvested fruit. Although of some pest status, both outdoors and in glasshouses, earwigs are also beneficial and will destroy large numbers of aphids and other pests.

BIOLOGY

Adult earwigs, reared during the summer or autumn, overwinter in the soil and mate in the early winter. In December or January, each mated female lays a batch of up to 100 eggs in an earthen cell (brood chamber); the maternal female then guards over the eggs and, later, the first-instar nymphs before eventually emerging. Nymphs developing from 'winter' eggs usually reach the adult stage by the early summer, individuals passing through four nymphal instars. The maternal females often deposit smaller batches of eggs in May or June, and nymphs arising from these eggs usually complete their development by the end of September. In parts of continental Europe, there may be three egg-laying periods annually. Earwigs are nocturnal insects, and usually hide during the daytime amongst curled leaves, under loose bark and in other sheltered situations.

DESCRIPTION

Adult female 12-14 mm long, chestnut-brown; posterior pincers slightly curved (see Fig. 18a). Adult male similar in appearance to female but larger; posterior pincers strongly curved (see Fig. 18b). Egg 1.3 x 0.8mm, oval, pale yellow. Nymph whitish or greyish to brown.

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