Armadillidium

Armadillidium is a genus of terrestrial isopod crustaceans in the family Armadillidiidae. It comprises several dozen species commonly known as pill bugs, pill woodlice, or roly-polies. Many Armadillidium species can roll into a nearly complete sphere when disturbed, a behavior called con globation; however, not all woodlice can fully roll up, and some Armadillidium species exhibit less complete rolling than others.

In appearance, Armadillidium species are small, dorsoventrally flattened crustaceans with a hard, segmented exoskeleton formed by overlapping plates. Adults typically measure about 8–12 millimeters in length, though sizes vary by species. Their color ranges from slate gray to brown, with species-specific markings in some cases. They have seven pairs of walking legs and specialized pleopods forming a brood pouch in females.

Ecology and life history: Armadillidium woodlice are detritivores, feeding on decaying plant matter, fungi, and algae. They inhabit moist microhabitats such as leaf litter, under logs, stones, and within compost, and require damp conditions to prevent desiccation. They are distributed across Europe, Asia, and parts of North America, with many species native to Eurasia and several introductions elsewhere. Reproduction is sexual; males transfer sperm to females, who brood eggs in a marsupium (brood pouch) formed by the abdominal plates. The juveniles hatch as mancae and molt through several instars to reach adult size.

Taxonomy and significance: The genus includes Armadillidium vulgare (the common pillbug) and other species such as A. nasatum and A. album. Armadillidium is of interest in ecological and ecotoxicological studies and plays a role in leaf litter decomposition and nutrient cycling in temperate ecosystems.