The pillbug, Armadillidium vulgare (Latreille), is an isopod, a type of non-insect arthropod also known as a terrestrial crustacean. It is sometimes called a roly-poly due to its ability to roll into ball when threatened or bothered. This defense behavior makes it look round like a pill, which is why it is sometimes known as a pillbug. The common name woodlice is a term used for both pillbugs and sowbugs in Europe. The name woodlice gives reference to where they can be found, such as under logs. These nocturnal creatures are mainly beneficial in the garden or landscape, but can become pests if they wander indoors.
Figure 1. Pillbug, Armadillidium vulgare (Latreille), adult and immatures. Photograph by Lyle Buss, University of Florida.
The pillbug is often mistakenly referred to as a sowbug, which is the common name used for other species of woodlice in the genera Oniscus and Porcellio. Both sowbugs and pillbugs are isopods, but they differ in that a pillbug can roll into a ball and a sowbug cannot. Sowbugs are more flattened and have a uropod (last segment of the abdomen) with exopods (lateral tail-like appendages that extend out beyond the pleotelson-the last segment), which makes rolling difficult.
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Authors: Julie A. Franklin, Morgan A. Byron, and Jennifer Gillett-Kaufma