Slaters Pillbugs and Woodlice: Isopoda

Physical characteristics: The bodies of common pill woodlouses are egg-shaped, with adults measuring up to 0.7 inches (18 millimeters). They are dark gray, brown to red and usually have distinct rows of spots. The antennae are visible from above, but the legs are not.

Geographic range: Originally from southern Europe and North Africa, this species is now found throughout the world in temperate climates.

Habitat: Common pill woodlouses are found in many different kinds of habitats, including forests, grasslands, and even coastal and desert sand dunes. They are very common in cultivated fields, gardens, and greenhouses. Most individuals are found under rocks, logs, and other objects where there is plenty of moisture.

Diet: They eat young plant shoots, as well as dead and decaying plant matter.

Common pill woodlouses roll up into a ball to protect their delicate undersides. (© Nigel Cattlin/Holt Studios Int'l/Photo Researchers, Inc. Reproduced by permission.)

Behavior and reproduction: Common pill woodlouses roll up into a ball to protect themselves. They move slowly on the ground in search of food and mates, traveling up to 43 feet (13 meters) a day under ideal summer conditions. During the winter they move only about half as far. During this time they may burrow as much as 10 inches (250 millimeters) beneath the surface of the soil.

Their reproductive cycles are triggered by rising temperatures and longer daylight hours. Mating usually occurs from late spring to early summer, sometimes even later in the year, just before the female goes through her molt. Females can store sperm in a special sac for up to one year. They produce one brood per year in the northern parts of their range, while those to the south produce two or three. Each brood has up to 100 eggs, but only half survive to become juveniles.

Common pill woodlouses and people: Large numbers of common pill woodlouses are sometimes considered pests in gardens and greenhouses because they will nibble on young plants.

Conservation status: Common pill woodlouses are not considered endangered or threatened. ∎