Oniscus asellus, the common shiny woodlouse - Porcellio spinicornis - Philoscia muscorum the Common striped woodlouse - Armadillidium vulgare the Pill bug
Oniscus asellus (above left) is often found under logs and in compost heaps. It is shiny grey with lighter grey patches, and its eyes consist of a number of black ocelli. It can reach 15 mm long and 7.5 mm wide, and is probably the most common British woodlouse, and is found anywhere there are damp conditions, it is also common in north and western Europe, and is present in eastern Europe and north America. It remains motionless when disturbed, but can run quite fast.
Above is Porcellio spinicornis, a particularly attractive woodlouse. Fully grown it reaches about 12 mm long. It has a black head, black eyes, a dark central stripe with a row of yellow blotches down either side. It can run quite fast, but usually stays still for a while when first disturbed. It is found in walls and buildings especially those with lime-rich mortar. It is very common in north east Scotland and in drystone walls in the Cotswolds, also northern France, northern Italy, Russia, Canada, and the USA.
Above is Philoscia muscorum, the Common striped woodlouse, which is common and fairly widespread. It is 11 mm long when fully grown, and a shiny mottled brown with a darker strip running down the middle of its back. Yellow, red and greenish individuals have been reported, though. The eyes consist of numerous black ocelli. It can run fast, and is found in hedgerows, grassland and tussocky grass in woodland and gardens, particularly on raspberry plants.
Armadillidium vulgare, the pill bug (above), can tolerate dry places, also its ability to roll up helps it conserve moisture. It can be found in grassy places, especially chalky and limestone areas, and is often confused with the pill millipede, but can be distinguished by its numerous small rear segments. When fully grown it can be up to 1.8 cm long. It is variable in colour, though most are light grey, but pink, black and yellow individuals have been seen. It is common in S E England and Ireland, throughout Europe, parts of Asia, North America, Australasia, South Africa and some Pacific and Atlantic islands. The pill bug was once used by doctors - that's where it gets its common name - patients had to swallow one whole!
As is the case in European woodlice, the eggs are laid and brooded in a pouch formed by the plates arising from the 2nd - 5th thoracic appendages. On hatching the young have just 6 pairs of legs, and are pale-coloured. They acquire the 7th pair of legs after their first moult, and by this time have left the brood pouch. Moulting occurs throughout their life, and usually takes place in crevices in the soil. They moult one half of the body at a time (see the Porcellio scaber photograph), with the rear half being moulted first. It can be as long as 2 weeks before the front half is moulted.