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Animal Fact Sheets

Pillbug range map



Classification and Range

Although their common names contain the word "bug," sowbugs and pillbugs are not really bugs. They're crustaceans, mostly aquatic invertebrates, such as the crab, lobster, crayfish and barnacle. Crustaceans breathe through gills, and have a hard exoskeleton and jointed appendages. Sowbugs and pillbugs are in the order Isopoda. They are technically termed isopods, which means "the legs are alike." Sowbugs and pillbugs are found in most regions of the world, and are widespread throughout North America.


Moist micro-climates, including damp, dark spaces and wooded areas. Prime habitats are under stones or in decaying wood. In cities, they frequent gardens, along house foundations and basements.

Physical Characteristics

Both animals are approximately 0.5 inch (12.5 mm) in length. They have one pair of jointed antennae, a flattened body, fused abdominal segments and seven pairs of legs. They are gray to brown in color and covered with armor-like plates, reminiscent of miniature armadillos. Like all crustaceans, sowbugs and pillbugs are wingless.

Life Span

Average about 2 years, but can live up to 5 years.


In the wild: Predominately vegetarian, but considered omnivorous, feeding on fungi and live or decaying vegetation and animals. During periods of drought, sowbugs and pillbugs are capable of switching to a scavenger-like diet.

At the zoo: Apples, oranges, romaine lettuce and monkey chow.


Sowbugs and pillbugs begin reproductive efforts in March and April. Two to three broods are raised during the summer. Each brood consists of 30-40 young, which are incubated for 34 days in the brood pouch. The brood pouch is located under the female's body, between the second and fifth pair of legs. The pouch is filled with fluid which protects the young while they are developing.

Life Cycle

Sowbugs and pillbugs are active parents. The male guards the family's burrow, while both parents gather food and clean the burrow of debris. It takes approximately one year for young to become adults (nymphs look similar to their parents). Once adults, sowbugs and pillbugs continue to molt approximately every 28 days. However, a breeding female molts less often to permit time to incubate her young. Sowbugs and pillbugs molt in two phases. First they lose the rear half of the exoskeleton, and approximately 12 hours later, they lose the front half. After molting, they eat the discarded exoskeleton shell to recycle the calcium, which will be used to strengthen their new exoskeleton.

Predators include many species of birds and some amphibians. To camouflage themselves from predators, sowbugs and pillbugs are colored to blend into their environment. As an added defense, the exoskeletons of pillbugs have 10 freely articulating segments that enable them to roll up into a ball. On the other hand, sowbugs lack the capability to roll into a ball; instead they flee to evade predators. Some species of sowbugs even secrete a noxious substance that discourages other animals from eating them.

Staying Wet Out of Water

Although they don't live in water, sowbugs and pillbugs are still highly dependent on water for survival. They need to stay moist to survive, so they actively scavenge for food only in the cool of the night. To prevent dehydration during the day, they seek dark, moist areas to hide and rest. Sowbugs and pillbugs often gather in groups, huddling together to reduce evaporation. Some even burrow into the ground to keep their gills wet. Gills are the primary breathing apparatus for all crustaceans, and must remain moist in order to function.

Amazing sowbugs and pillbugs are on view at Woodland Park Zoo's Bug World. You'll go "buggy" while viewing exciting seasonal displays that take you on a journey to different bioclimatic zones around the world. You may come face-to-face with recycling cockroaches, assassin bugs, web-spinning spiders or scuba diving beetles, to name only a few. The only way you'll find out which bugs you'll encounter is by visiting Bug World. Don't miss it!


Conservation Connection

Sowbugs and pillbugs are often considered pests in greenhouses because they nibble at the roots of stems and seedlings. However, sowbugs and pillbugs are valuable arthropods because they provide food for other animals. As scavengers, they also play a critical role in maintaining the health of their environment. They return nutrients to the soil when they eat decaying matter and then defecate. In gardens, they benefit humans by circulating soil without eating garden plants.

How You Can Help!

The effort to save animals and their habitat requires cooperation and support at the international, national, regional and individual levels. You can help in this cause. Join and become active in Woodland Park Zoo and other conservation organizations of your choice. To conserve habitat for sowbugs, pillbugs and other arthropods, reduce your use of pesticides and herbicides, and work to preserve vegetation in your neighborhood and in tropical regions.

Contact Woodland Park Zoo at to find out how you can support conservation efforts at the zoo. Learn other ways you can help conserve wildlife and the habitats they require for survival by visiting our How You Can Help page.

Sources and Suggested Reading

Burnette, Robin. 1992. The PillBug Project: A Guide to Investigation (teacher's packet). National Science Teachers Association. 100 p.

For Kids!

Ricciuti, Edward R. 1994. Crustaceans. Blackbirch Press, Inc., Woodbridge, CT. 64 p.


Sowbug and Pillbug Fascinating Facts

  • Sowbugs and pillbugs lack spiracles (small openings on the sides of their bodies used for respiration), which are possessed by many other arthropods!
  • Like reptiles and amphibians, all arthropods, including sowbugs and pillbugs, are cold-blooded. Their body temperature is regulated by the temperature of their environment!