The pillbug on the other hand has a rounder back, from side to side, and a deeper body, from back to legs. When disturbed, it frequently rolls into a tight ball, with its legs tucked inside, much like its larger but dissimilar counterpart the armadillo.

Sowbugs have gills which need constant moisture, so they tend to live in moister northwest climates. They are primarily nocturnal, and eat decaying leaf litter and vegetable matter. They may also feed on the tips of young plants, so can be considered pests, but they also help the environment by breaking up decaying plant matter and help speed up the recycling of the nutrients they contain.