Woodlice

Definition

Terrestrial isopod crustaceans in the suborder Oniscidea, characterized by a dorsoventrally flattened, segmented exoskeleton with seven pairs of walking legs and the ability to conglobate (roll into a ball) in many species. Despite their common name suggesting parasitic insects, woodlice are free-living detritivores that occupy moist microhabitats under bark, stones, and leaf litter, functioning as important decomposers in soil ecosystems.

Etymology

From 'wood' + 'louse,' the latter from Middle English lous, referring to the superficial resemblance to parasitic lice; the name predates recognition of their crustacean affinities.

Example

The common rough woodlouse (Porcellio scaber) and the pill woodlouse (Armadillidium vulgare) are frequently encountered in garden compost heaps, where they fragment decaying plant material and accelerate nutrient cycling.

Synonyms

• slater
• sow bug
• pill bug
• wood pig

Related Terms

• isopod
• Oniscidea
• crustacean
• Detritivore
• conglobation
• malacostracan

Usage Notes

Regional common names vary considerably: 'pill bug' and 'roly-poly' typically refer to conglobating species (e.g., Armadillidium), while 'sow bug' often denotes non-conglobating genera like Porcellio. In formal taxonomy, 'woodlice' is not a monophyletic group but a functional ecological grouping of terrestrial Oniscidea. Specialists distinguish woodlice from aquatic isopods (e.g., Asellus) and from other peracarids such as amphipods.