Woodlouse

Woodlice Temporal range: Early Cretaceous–present, 113–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Clockwise from top right: Ligia oceanica, Hemilepistus reaumuri, Platyarthrus hoffmannseggii and Schizidium tiberianum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Order:	Isopoda
Suborder:	Oniscidea Latreille 1802[1]
Sections
Diplocheta Tylida Microcheta Synocheta Crinocheta

Woodlice are terrestrial isopods in the suborder Oniscidea. Their name is derived from being often found in old wood,^[2] and from louse, a parasitic insect,^[3] although woodlice are neither parasitic nor insects.

Woodlice evolved from marine isopods which are presumed to have colonised land in the Carboniferous, though the oldest known fossils are from the Cretaceous period.^[4] This makes them quite unique among the crustaceans, being one of the few lineages to have transitioned into a fully terrestrial environment.

Woodlice have many common names and although often referred to as terrestrial isopods, some species live semiterrestrially or have recolonised aquatic environments like those of the genus Ligia. Woodlice in the families Armadillidae, Armadillidiidae, Eubelidae, Tylidae and some other genera can roll up into a roughly spherical shape (conglobate) as a defensive mechanism or to conserve moisture; others have partial rolling ability, but most cannot conglobate at all.

Woodlice have a basic morphology of a segmented, dorso-ventrally flattened body with seven pairs of jointed legs, and specialised appendages for respiration. Like other peracarids, female woodlice carry fertilised eggs in their marsupium, through which they provide developing embryos with water, oxygen and nutrients. The immature young hatch as mancae and receive further maternal care in some species. Juveniles then go through a series of moults before reaching maturity. Mancae are born with 6 segments and gain an additional one after their first molt.

While the broader phylogeny of the Oniscideans has not been settled, eleven infraorders/sections are agreed on with 3,937 species validated in scientific literature in 2004^[5] and 3,710 species in 2014 out of an estimated total of 5,000–7,000 species extant worldwide.^[6] Key adaptations to terrestrial life have led to a highly diverse set of animals; from the marine littoral zone and subterranean lakes to arid deserts and desert slopes 4,725 m (15,500 ft) above sea-level, woodlice have established themselves in most terrestrial biomes and represent the full range of transitional forms and behaviours for living on land.

Woodlice are widely studied in the contexts of evolutionary biology, behavioural ecology and nutrient cycling. They are popular as terrarium pets because of their varied colour and texture forms, conglobating ability and ease of care.

Recent research has shown that the grouping as traditionally defined may not be monophyletic, with some taxa like Ligia and possibly Tylidae more closely related to other marine isopod groups, though the majority of woodlice probably do constitute a clade.^[7][8]