Further Information
The common woodlouse (Oniscus asellus) is one of the commonest and widely spread of the British woodlice. Woodlice are not insects, but are crustaceans; more closely related to crabs and shrimps than they are insects. The body is divided into three main regions, the head, the thorax (known in woodlice as the 'pereion'), and the abdomenn ('peon').
The common woodlouse is typically grey with irregular light patches, but yellow and orange forms may occur near to the sea. At around 16mm in length, the surface of the body is dotted with raised blotches. Adults usually have a glossy body, but in contrast juveniles often have a rough body texture.
Woodlice feed on dead organic matter, which they detect by means of taste and smell. The common woodlouse is gregarious and typically spends the day concealed beneath stones, logs and other objects. When threatened, this species defends itself by clamping down onto the surface; the feet can grip the substrate very tightly, enabling it to cling on tenaciously.
Mating tends to take place at night, and is very rarely observed for this reason. When a male finds a receptive female, he climbs onto her back and drums her with his front legs whilst 'licking' her head with his mouthparts. He moves to one side of the female, bending his body beneath hers, and transfers sperm to one of the female's genital openings. He then moves to the other side and transfers sperm to the remaining genital opening. During the breeding season, reproductive females develop a 'brood pouch', which consists of overlapping leaf-like structures known as 'oostegites', which form a 'false floor' below the body. The fertilised eggs pass into this fluid-filled chamber and the young crawl out of the brood pouch when they are fully developed. They undergo a series of moults before reaching maturity, growing at each stage; the stages between these moults are known as 'stadia', and are generally similar in structure and appearance.
Mature woodlice continue to moult; prior to moulting, the calcium contained in the old cuticle is removed and stored as conspicuous white blotches, these blotches disappear after moulting as the calcium is used to reinforce the new cuticle. The rear part of the body moults a few days before the front half, and occasionally woodlice may be seen with half a pinkish body and half a 'usual' grey body for this reason. The discarded cuticle is frequently eaten by the newly moulted woodlouse.
Woodlice as a pest
The common woodlouse does not bite, does not carry disease and therefore presents no real health risk to humans. However, they frequently enter houses through small gaps in brickwork and under doors etc. and are clearly an unpleasant sight walking across lounge and kitchen floors.
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