Sowbugs

Definition

Terrestrial isopod crustaceans in the suborder Oniscidea, characterized by a dorsoventrally flattened, oval body and seven pairs of walking legs. Unlike their close relatives the pillbugs (Armadillidiidae), sowbugs cannot roll into a complete ball; they possess two prominent tail-like uropods projecting from the posterior and tend to have a more flattened body profile. They are obligate decomposers in moist soil and leaf-litter habitats, functioning as key detritivores in nutrient cycling.

Etymology

From Middle English 'sough' or 'sow' (swine, pig) + 'bug', referring to the pig-like habit of rooting through soil and decaying matter.

Example

In a temperate forest floor survey, sowbugs such as Oniscus asellus aggregate under decaying logs where they fragment leaf litter and facilitate microbial decomposition, whereas the sympatric pillbug Armadillidium vulgare rolls defensively when disturbed.

Synonyms

• Woodlice
• terrestrial isopods

Related Terms

• Pillbugs
• isopods
• detritivores
• uropods
• Oniscidea
• soil mesofauna

Usage Notes

In North American vernacular, 'sowbug' and 'pillbug' are often used interchangeably, but specialists distinguish them by defensive behavior and uropod presence. Sowbugs are more flattened and have visible tail-like appendages; pillbugs are more convex and lack projecting uropods. Both groups are crustaceans (Malacostraca), not insects, despite their terrestrial habits. The term is sometimes spelled 'sow bug' in two words.