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Woodlice are terrestrial in the suborder Oniscidea. Their name is derived from being often found in old wood, and from louse, a parasitic insect,
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. This makes them quite unique among the , 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 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, Dorsoventrally flattened body with seven pairs of jointed legs, and specialised for respiration. Like other Peracarida, female woodlice carry fertilised eggs in their marsupium, through which they provide developing with water, oxygen and nutrients. The immature young hatch as and receive further maternal care in some species. Juveniles then go through a series of Moulting before reaching maturity. Mancae are born with six segments and gain an additional one after their first molt.
While the broader phylogeny of the Oniscideans has not been settled, eleven /sections are agreed on with 3,937 species validated in scientific literature in 2004 and 3,710 species in 2014 out of an estimated total of 5,000â7,000 species Extant species worldwide. 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 above sea-level, woodlice have established themselves in most terrestrial 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 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.
Common names include:
A female woodlouse will keep fertilization eggs in a marsupium on the underside of her body, which covers the under surface of the thorax and is formed by overlapping plates attached to the bases of the first five pairs of legs. They hatch into offspring that look like small white woodlice curled up in balls, although initially without the last pair of legs. The mother then appears to "give birth" to her offspring. A few species are also capable of reproducing asexually."How Now, Sow Bug?," Discover, August 1999, 68.
Despite being Crustacean like lobsters or crabs, woodlice are said to have an unpleasant taste similar to "strong urine". This is due to their high concentration of uric acid, which is one of the chemicals in urine. Their flavor has also been compared to shellfish.
These two groups can be distinguished in several ways. Glomeris millipedes have 19 (males) or 17 (females) pairs of legs, while pill bugs only have 7 pairs of legs. Additionally, pill bugs have a thorax consisting of 7 body segments, 5 abdominal segments, and a Telson, while Glomeris millipedes lack a visually defined thorax and have 12 body segments total. While the Uropod of pillbugs are relatively quite small, flipping a pill bug over will reveal the small uropod overlapping the pleotelson. Some woodlouse species, like Armadillidium maculatum, seem to display Batesian mimicry to certain pill millipedes like Glomeris marginata.
A 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 of Trichoniscidae and Thailandoniscus annae (family Styloniscidae). Species for which aquatic life is assumed include Typhlotricholigoides aquaticus (Mexico) and Cantabroniscus primitivus (Spain).
Woodlice are eaten by a wide range of , including spiders of the genus Dysdera, such as the woodlouse spider Dysdera crocata, and of the genus Luteostriata, such as Luteostriata abundans.
Woodlice are sensitive to agricultural , but can tolerate some toxic heavy metals, which they accumulate in the hepatopancreas. Thus they can be used as of heavy metal pollution.
Woodlice can also invade homes in groups searching for moisture, and their presence can indicate dampness problems. They are not generally regarded as a serious household pest as they do not spread disease and do not damage sound wood or structures. They can be easily removed with the help of vacuum cleaners, chemical sprays, insect repellents, and insect killers, or by removing the dampness.
While some isopod species are kept purely as pets, some can also be used as an addition to bioactive terrariums, due to their ability to break down decaying organic materials.
Some isopod morphs are characterized by Polygenic trait traits, such as 'Orange Vigor' ( Armadillidium vulgare) and 'Pink Rubber Ducky' ( Cubaris sp. "Rubber Ducky"), the result of selectively breeding isopods that best match the desired appearance. These genes can vary in their expression greatly, as they are not the result of a specific genetic mutation.
Other morphs are the result of dominant or recessive mutations, as seen with 'T+/Tâ Albinism' and 'Whiteout' (several spp.). As an example, T+ albino isopods are the result of an isopod being born without the ability to produce melanin, removing all black pigmentation. However, they are believed to be tyrosinase-positive (hence the T+), and therefore can still create some darker pigments such as brown and purple. Tâ albino isopods are thought to lack both melanin and tyrosinase, and therefore only express light yellows, oranges, and white.
Confusion can often arise due to the rate at which unidentified or undescribed isopod species are introduced to the hobby. This has contributed significantly to the genus Cubaris being considered a wastebasket taxon, as many of the unidentified or undescribed isopod species are incorrectly labelled as " Cubaris sp." even when they do not fit the formal description of the genus.
Section: Crinocheta
Beyond these, some genera are of uncertain familial assignment such as:
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