A woodlouse is a crustacean with a rigid, segmented, long exoskeleton and fourteen jointed limbs. Woodlice form the suborderOniscidea within the order Isopoda, with over 3,000 known species.
The woodlouse has a shell-like exoskeleton, which it must progressively shed as it grows. The moult takes place in two stages; the back half is lost first, followed two or three days later by the front. This method of moulting is different from that of most arthropods, which shed their cuticle in a single process. Metabolic rate is temperature-dependent in woodlice. In contrast to mammals and birds, invertebrates are not "self heating": the external environmental temperature relates directly to their rate of respiration.
A female woodlouse will keep fertilised eggs in a marsupium on the underside of her body until they hatch into small, white offspring. The mother then appears to "give birth" to her offspring. Females are also capable of reproducingasexually.[19]
Living in a terrestrial environment, woodlice breathe through trachea-like lungs in their paddle-shaped hind legs (pleopods), called pleopodal lungs. Woodlice need moisture because they rapidly lose water by excretion and through their cuticle, and so are usually found in damp, dark places, such as under rocks and logs, although one species, Hemilepistus reaumuri, inhabits "the driest habitat conquered by any species of crustacean".[21]They are usually nocturnal and are detritivores, feeding mostly on dead plant matter.
Few woodlice have returned to water. Evolutionary ancient species are amphibious, such as the marine-intertidal sea slater (Ligia oceanica), which belongs to family Ligiidae.
Other examples include some Haloniscus species from Australia (family Scyphacidae), and in the northern hemisphere several species ofTrichoniscidae and Thailandoniscus annae (family Styloniscidae). Species for which aquatic life is assumed include Typhlotricholigoides aquaticus(Mexico)