Pillbugs

By Joe Merkelbach (October 2006)

Pillbugs – or sowbugs, roly-polys, woodlice or potato bugs in some parts of the country – are commonly seen critters whenever plants and pots that have been outside for warm weather are picked up to be moved back indoors. The bugs like the cool, humid, dark conditions beneath pots and other objects, and so congregate there during daytime hours.

Although they look like insects, pillbugs are actually land-dwelling crustaceans. They breathe with modified gills located on their rear sets of legs and must have moist conditions to maintain themselves. They have the unusual ability to restore lost body moisture by absorbing water from humid surroundings, and so seek out proper microhabitats.

Along with insects, spiders, millipedes, centipedes and others, pillbugs are members of the phylum arthropoda, meaning joint-legged. As a group, they are called isopods, meaning same-legged, because they do not have forelegs modified into claws as other crustaceans.

Pillbugs are the isopods that can roll up into spherical shapes when disturbed, while sowbugs contort into a “C” shape, or generally prefer to scurry away. Many species of aquatic isopods look similar to pillbugs, although they can be much larger.

The pillbug species we see domestically are all immigrants from Europe thought to have arrived in North America with shipped-in wood materials. These species are used to living in close proximity to human dwellings and artifacts. There are also native American species, which are residents of the leaf litter in forests away from human habitation. These bugs are most properly termed woodlice.

All the references I reviewed said that isopods feed on dead organic matter, such as leaf litter, and do not generally attack live plant tissue. Pillbugs can climb into pots through drainage holes and eat dead root ends, but it is doubtful that they damage our plants. They even contribute in a small way to the creation of new soil.

Simply lifting the bottom surfaces of pots above ground on racks or mesh to expose the bottoms to air circulation and drying is enough to cause pillbugs to seek other, more hospitable conditions. This is a good method for clearing plants of pillbugs before taking them inside.

Considering their interesting habits and benign nature in relation to summering plants, the use of insecticides on pillbugs does not seem warranted.