Being crustaceans, pill bugs are ill adapted to life out of water—unlike insects and arachnids—so they spend most of their time under rocks or logs, around compost piles, and in other consistently moist areas. They're members of nature's cleanup crew, subsisting on water-soaked organic matter like carrion, dung, and rotting vegetation when they venture out on cool, wet nights. Sharing sleeping habits and quarters with more damaging pests like slugs, they are often blamed for damage done after rain washes away slime trails.
When conditions are right—that is, cool and wet—populations explode, and pill bugs can become noteworthy pests. They do their worst damage in damp springs as seeds germinate. They can mow down an entire bed of emerging seedlings in a single night, especially beds with lots of compost or leaf litter on the soil. Tender roots and shoots are sometimes munched as well. Pill bugs may crawl into planters, basements, and garages in search of dead things to eat, becoming unwanted houseguests.
To combat established populations, try a strategy that also works against slugs and snails: beer. Pour an inch of beer into the bottom of a small dish with its lip at the soil level; pill bugs will crawl in and drown.
As with many pests, however, the best way to safeguard plants is through preventive tactics, such as eliminating suitable habitat for pill bugs. Apply compost or leaf mulch to planting beds only after seedlings are up and growing. Move woodpiles or other nesting sites away from the garden. Pull mulch 8 to 12 inches away from the foundation and caulk cracks and crevices to prevent entry into homes. Prevention goes a long way in keeping pill bugs from becoming a tough pill to swallow.
Originally published in Organic Gardening Magazine, Oct/Nov 2013