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Graphic: What About Pillbugs

Photo: Pill Bug Drawing
Pillbugs live beneath stones, boards, and decaying vegetation.

Graphic: Background Information

What are pillbugs?
Have you ever turned over a rock or an old board in your backyard and discovered underneath a small, hard-shelled creature that resembles a miniature armadillo? When you picked up the bug in your hand, did it roll up into a near-perfect ball? Such armored creatures are called sow bugs, and the kind that roll up into a ball, or pill shape, often are called pillbugs. Technically, sow bugs and pillbugs are known as isopods, which means "the legs are alike." Isopods are not insects, but crustaceans - land-dwelling relatives of crabs and lobsters.

What do pillbugs look like?
Pillbugs are wingless, oval or slightly elongated isopods about 1/2 inch long. They are colored a slate-gray, and their body segments resemble armored plates. Pillbugs, or "roly-polys," have three body parts: head, thorax, and abdomen. They also have seven pairs of legs.

How do pillbugs live?
Pillbugs are slow-moving, crawling creatures, and they are cold-blooded, which means their body temperature is regulated by the surrounding environment. In the Columbia Basin, you can find pillbugs in many places, but particularly in gardens, along house foundations, and sometimes in basements. Although these creatures are common, you rarely see them during the day because they prefer dark, moist places - under rocks, boards, bricks, trash, decaying vegetation, or just beneath the soil surface. Mulches, grass clippings, and leaf litter often provide the decaying organic matter these creatures need to survive. Only at night do they emerge to wander around.

Pillbugs can breed throughout the year. The female carries the eggs in a brood pouch on the underside of her body. Often, there are as many as 200 eggs per brood. The eggs hatch in 3 to 7 weeks, and the young remain in the pouch another 6 to 7 weeks. Once the young leave the pouch, they never return. Some species produce only one brood per year, but others may produce two or more.

Isopods, like insects and their relatives, must shed their hard outer skin or exoskeleton to grow. They do this a dozen or more times during their lives. Pillbugs generally hide when they shed their skin because they are especially vulnerable to enemies at this time. The average life span of most isopods is about 2 years, but some have lived as long as 5 years.

Graphic: Shrub-Steppe Logo

Graphic: Notes..."Science is constructed of facts as a house is of stones. But a collection of facts is no more a science than a heap of stones is a house." Henri Poincare

Keep in mind this fact sheet is intended to be used only as background information to support your effort to encourage inquiry-based science, which parallels the way scientists uncover knowledge and solve problems.

Graphic: Suggested Activities

1. Armed with a flashlight and jar, you can easily find and collect pillbugs in the backyard. You also can trap them using a whole potato as bait.
Here's how: To make the potato trap, bore a 3/4-inch hole through the potato lengthwise, then close up one end of the hole with a small piece of the potato plug. Place the "trap" in the garden or any other place where sow bugs and pillbugs are abundant. Cover the trap with leaves, and leave it alone a few days. The pillbugs will come and feed inside the hole in the potato. To remove them, place the opening over a jar, and strike the potato to dislodge them. The potato trap is especially useful for collecting small or young isopods and rare species, too.

2. Test pillbug responses to moisture.
Here's how: Take a batch of medium to large pillbugs (8-10 specimens) and place them in a petri dish or jar on dry filter paper. Keep the container in dim light, and observe the reaction of the bugs for 2-3 minutes. How do the pillbugs react? Record your observations. Now put the same pillbugs in a container with just a small piece of damp paper. What do you observe? Why do you think pillbugs reacted the way they did? Think about where you find pillbugs - in damp or dry areas? Did you know that pillbugs have gills and they do not retain water well? Within a minute or two you should have seen them clump together when they were placed on the dry paper, indicating a need to reduce water loss from their bodies. Most pillbugs act "normally" when the relative humidity is moderately high (50-70%), the light is dim, and the temperature is close to indoor conditions or slightly lower.

3. Test pillbug responses to temperature.
Here's how: Place four to six pillbugs in a small jar with a cover, and float the jar on water in a pan. Add ice cubes and a thermometer, and stir gently so as not to tip the jar. Observe the reaction of the pillbugs. Now remove the ice cubes, and gently heat the water. After 1 minute, note the temperature on the thermometer and write down the reaction of the pillbugs. Continue to record the temperature and your observations. Once the temperature gets close to 40°C remove the pillbugs or they will go into heat stupor, which may kill them. Did you know that pillbugs slow down their movements and may even stop moving as the temperature approaches 0°C? Pillbugs will speed up their movements as the temperature rises and they become frantic by the time the temperature reaches 40°C.

(Experiments by Louis F. Wilson, Michigan Entomological Society, Department of Entomology, Michigan State, University, East Lansing, Michigan 48823.)

Graphic: Other Resources

  1. The Pillbug Project, Grades 3-7, National Science Teachers Association, 3140 N. Washington Blvd., Arlington, Virginia.
  2. Project Wild, Grades 1-12, P.O. Box 18060, Boulder, Colorado.
  3. Rolypolyology (Backyard Buddies), Michael Elshohn Ross, 1995. Carolrhoda Books, Minneapolis, Minnesota.

Graphic: Web Sites...

  1. Isopod, Pillbug, Sow Bug Information -
  2. Pillbug: An Isopod -
  3. Sowbugs and Pillbugs -
  4. The Pillbug Project -

Graphic: Acknowledgements

Initial development and printing of this fact sheet was funded by an Eisenhower Grant to the Partnership for Arid Lands Stewardship. Written by: Randy Reed; Series Editor: Georganne O'Connor; Design: WinSome Design; Printing: Eagle Printing and Graphic Design; First Printing: December 1997; Web Development: WinSome Design.

Graphic: Shrub-Steppe Ecology Series


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