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Minibeast Profiles: Sowbugs and Pillbugs
by Gary A. Dunn, M.S., F.R.E.S., Director of Education
Sowbugs and pillbugs (sometimes called "woodlice" or "rolypolies") belong to the arthropod class Crustacea and are closely related to the shrimps, crabs, lobsters, crayfish, and barnacles. The sowbugs and pillbugs (order Isopoda) are the only members of this group that are terrestrial and do not live in the water.
The sowbug (Porcellio spp.) has seven pairs of legs and measures about 13 mm (1/2 inch) in length. The body is grayish or brownish and composed of segmented, overlapping plates. There are two pairs of antennae (only one pair readily visible), well-developed eyes, and a group of short appendages at the tip of the abdomen.
Sowbugs, Porcellio sp.
The pillbug (Armadillidium sp.) is similar to the sowbug, but is generally larger (15 mm - 2/3 inch), darker (dark slate gray), and has no appendages at the tip of the abdomen. Pillbugs are capable of rolling themselves into a neat, circular ball ("pill") for protection; sowbugs generally prefer to scurry away (at most they can curl into a C-shaped posture).
The biologies of these two isopods are very similar, and they will be discussed together. Sowbugs and pillbugs are generally found in leaf piles and compost heaps, in rotting logs, and under stones. At night they become very active and wander about in search of food. They may also be common near buildings, especially where it is dark and damp, and may be found in basements, crawl spaces, garages, sheds, around wells and cisterns, and under all types of debris. Their diet consists of various plant materials, usually moist, decaying vegetation. They are also known to feed on living plants (garden crops, flowers, and fallen fruit), and even some animal materials (manure, carrion, and other sowbugs).
Sowbugs and pillbugs overwinter as adults. Mating occurs in the spring (April to June), and the female carries the eggs in a special brood "pouch" located on the underside of the body. The eggs mature over a period of 50 to 90 days and then hatch. The immatures are similar to the adults, except that they are smaller in size, lighter in color and sometimes have fewer legs. Generally speaking, it takes a full year for the immatures to reach adulthood. The adults may live for 2 or 3 years if the environment is favorable.
REFERENCES
If you would like to learn more about sowbugs and pillbugs, I recommend the following books:
- Keeping Minibeast. Woodlice and Millipedes. Barrie Watts. Franklin Watts. New York. 1991.
- Pillbugs (Life Cycles). Donna Schaffer. Capstone Press. Mankato MN. 24pp., illust.
- A Pillbug's Life. John Himmelman. Children's Press. New York NY. 1999. 28pp., illust. (color art)
| This educational resource was prepared by the Young Entomologists Society, 6907 West Grand River Ave., Lansing MI 48906-9131, phone/fax 517-886-0630, e-mail YESbugs@aol.com. Support minibeast youth education - join Y.E.S. today! |