Where do pillbugs come from? I haven’t seen any live ones now that the weather has gotten colder but there sure are a lot of dead ones rolled up in the corner of my basement!

Z. O., Dedham, MA

You call them pillbugs, some call them roly-polys, and they’re often confused with the closely related sowbugs (see Sowbug or Pillbug? It’s Just a Chucky Pig!). Pillbugs aren’t insects, they’re crustaceans and actually more closely related to shrimp! When threatened, both pillbugs and sowbugs roll up into a protective ball.

Pillbugs Are Common in Damp Mulch

As to where they come from, I’m sure you know that they’re getting into your house from outside where they’re found in damp places such as under mulch, leaves, or compost, or beneath stones or bark. That’s why they are also known as woodlice, although they are not related to lice at all. Like millipedes and a lot of other foundation pests, they feed on decaying plant material. In large numbers, they can damage roots and stems of young garden plants.

Like other “occasional invaders,” pillbugs and sowbugs move inside when it gets too dry, or even too wet, in their outside environment (see Pillbugs Can Move Inside). They’re able to get into your home through gaps around patio doors or ground floor doors, garage doors, or window wells. They can also get in through other foundation openings such as unscreened vents or gaps around cables or lines that enter the house. And sometimes they are simply carried inside hidden in potted plants or firewood.

Maybe because they are crustaceans and are related to crayfish, pillbugs need a moist environment. Although they enter homes seeking moisture, they usually find just the opposite. Indoor environments are almost always drier than outdoors and pillbugs and sowbugs die fairly quickly from lack of moisture inside. This is also the reason why they are found almost exclusively on damper lower levels in basements and crawlspaces, and in garages.

Tighten Doors to Help Keep Pillbugs Out

To reduce the number of pillbugs in your home, seal openings where they enter by adding door thresholds and sweeps (see Pestproofing Doors to Keep Pests Out). Reduce the number of pillbugs around the outside foundation of your home by using less mulch and removing piles of leaves and grass. Colonial offers a semi-annual exterior treatment as part of our Preventative Maintenance Program that eliminates foundation pests before they can move indoors. Give us a call for more information.