Our house keeps getting invaded by those gray roly-poly bugs that curl into a ball. When we were kids, we called them pillbugs, but when I looked them up on the Internet, I found “sowbugs” instead. Whatever they are, how can we get rid of them? A. G., Deerfield, NH

Pillbugs and sowbugs are actually two different pests that look alike. Despite the names, they’re technically not bugs but are crustaceans, more closely related to crayfish than insects. Pillbugs can curl into a protective ball when disturbed but sowbugs can’t. Both of these pests occur in the same areas and have the same habits so it’s not important to be able to tell them apart for control purposes.

Where Do Pillbugs Come From?

Pillbugs belong in a group known as foundation pests which also includes millipedes, earwigs, centipedes, and crickets. Pillbugs are scavengers feeding on decaying plant material. They live in dark, damp, moist areas and are often found around the foundation of a home where heavy mulch, ground cover plants, and leaf cover provide the ideal environment. They are also sometimes called woodlice (no relation to headlice) since they are common in wooded areas with leaf litter and rotting wood.

The pillbug is also known as an occasional invader since it will move into buildings when outside conditions change and are becoming drier, wetter, or colder. Pillbugs often move inside seeking moisture but instead die fairly quickly from drier indoor air. If pillbugs are surviving long-term indoors, that’s an indication that there is a moisture problem in your home that needs to be addressed (see Pillbugs Like the Damp Areas of Your Home).

Seal Openings To Keep Pillbugs Out

Because they don’t survive or reproduce indoors, and don’t damage anything indoors, generally the only control required is pest-proofing measures to keep them out. If you have large numbers moving in or living outside around your foundation, an exterior insecticide treatment around the foundation can reduce their numbers (Colonial Pest can do that for you!).

Pest-proofing or pest exclusion is something that can be done by a professional (we also do that at Colonial Pest!) or you can handle it yourself. Caulk openings around the foundation and screen foundation vents. Adding door thresholds on lower levels and garage door seals are two important pest exclusion measures that will keep lots of pests out, including pillbugs. Cleaning up stacks of building materials or firewood and removing heavy mulch and piles of leaves or grass clippings will remove outside hiding places for pillbugs.

Photo credit: F.E.Wood, Univ. of Md. Entomology