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Common Name: Pill Woodlouse

Scientific Name: Armadillidium vulgare


Kingdom: Animalia

Phylum: Arthropoda

Class: Crustacea

Order: Isopoda

Family: Armadilidiidae

Genus: Armadillidium

Species: A. vulgare


Pill woodlouse is the common name for Armadillidium vulgare. Even more common names for pill woodlice include roly-poly, doodlebug, and potato bug. It got its nickname “roly-poly” by how it rolls into a ball-like form when threatened by predators. Pill woodlice can grow up to 18 mm. Their colors vary, but most are slate gray. The antennas are visible from the top, but the legs are not. Although woodlice are terrestrial crustaceans, several forms have returned to the water. Most of these are amphibious, but some have become truly aquatic. The way they roll into a ball-like form is actually an advantage. Evaporation from the lower surface is greatly reduced, which helps them survive short periods of drought. This also makes it more difficult for shrews and other small predators to get at, because the balls are too large for their jaws. The pill woodlouse and the pill millipede are often confused with each other. However, the millipede is much blacker and glossier. When it is active, it has more than seven legs, which is how many legs woodlice have. When they are rolled up, the woodlouse’s segments are smaller at the rear. The millipede’s plates are the same size at the rear.


There are 37 native species in the United Kingdom, ranging in color and size. They are originally from southern Europe and North Africa. They are found in many different kinds of habitats, including forests, grasslands, and even coastal and desert sand dunes. Most are found under rocks, logs, and other objects where there is plenty of moisture. They eat young plant shoots, as well as dead and decaying plants. Rising temperatures and longer daylight hours trigger their reproductive cycles. 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. A female woodlouse will keep fertilized eggs in a patch on the underside of her body until they hatch into small, pink offspring. So, those cute little rolled up bugs that kids play with really have a great deal of scientific impact.


Author: Diana R

Published: 02/2008

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