Woodlouse

Article

November 30, 2021

Woodlice or porcellions are crustaceans forming the suborder Oniscidea in the order Isopods, with more than 4000 known species, including 218 in France. The most common species is the common woodlouse (Armadillidium vulgare).

Features

Woodlice are the only crustaceans entirely terrestrial, and live mainly under old stumps or under dead leaves, in order to protect themselves from the sun. They have a rigid, segmented exoskeleton, which is pale yellowish-brown (rather in young people) to blackish to slate gray. Their shell is sometimes almost transparent. It is composed of limestone, calcium phosphate and chitin.

Morphology

The body of woodlice is made up of different metamers associated in three different parts: the head, thorax and abdomen. The head, or cephalon, carries the sensory organs (compound eyes, two pairs of antennae, one of which is very small and difficult to observe) and the mouth parts. The thorax, or perion, is made up of 7 segments. The ventral part of each segment carries a pair of walking legs. The woodlouse thus has 14 legs. This easily observable criterion makes it possible to differentiate it from insects. The abdomen, or pleon, made up of 5 segments, carries the respiratory and reproductive organs. Woodlice breathe through gills contained in small pockets filled with water. These pockets are limited by thin membranes allowing the exchange of respiratory gases with the atmosphere.

Food

Wood lice are detritiphages that feed on decaying plant material. They thus contribute to the recycling of the necromass and allow a faster return of the nutrients in the soil. They can also attack living plants, roots, fruits, etc., but they do not represent a threat to crops. In breeding, you can give them all types of fruits and vegetables. They also love fish glitter. They also need a source of calcium to develop their shell, so cuttlefish bones are widely used in the rearing of woodlice.

Life cycle and reproduction

Woodlice live between 2 and 4 years, moulting monthly. They reach sexual maturity at the age of 3 months to 1 year, depending on the species. A female woodlouse keeps the fertilized eggs below her body in an incubator pocket called a marsupium. After a month of incubation, the mother then seems to "give birth" to her offspring (see video opposite).

Behavior

Some species of woodlice can curl into a ball when they feel threatened, leaving only their armored backs exposed (volvation). They are distinguished from glomeris (centipedes) by the greater number of tergal plaques when they are in a ball. Woodlice can form large aggregates that allow them to resist desiccation longer. This aggregation behavior observed in woodlice is a first step in the evolution of sociality (demonstrated in Porcellio scaber). Some desert species, for example Hemilepistus reaumuri, live in families or in pairs and raise their young in a burrow.

Habitat

Woodlice are lucid and usually nocturnal. This prompts them to seek out dark, damp places which they colonize in groups. They are found, for example, under leaves or bark, in dead wood, in rock crevices or in caves and in the trumpets of death. A study of soil macroinvertebrates in Mediterranean forest and southern Russia, from 144 intact soil samples (76 cm2 each), showed an average isopod abundance of 166,

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