The little blue-gray creatures that live under rocks and logs and roll into a ball when disturbed go by many names, including roly-poly bugs, pillbugs, woodlice, tiggy-hogs, parson-pigs and by their scientific name, Armadillidium vulgare. Roly-poly bugs are important for their part in decomposition, but they are not bugs. According to the University of Michigan website, people even like to keep them as pets.
Even though the name implies that these creatures are bugs, they are not insects. Roly-poly bugs are crustaceans. They are in the isopod family (same pod or foot) and have seven pairs of legs that are all similar in size and shape. According to the University of Arizona, roly-poly bugs also have simple eyes; three main body parts -- head, thorax and abdomen; uropods; a pair of prominent antennae; gills; and lunglike adaptations. As terrestrial creatures related to marine animals, they need moisture to survive but cannot live submerged in water.
Female roly-poly bugs may have one to three broods of young per year. When the eggs are formed, the female places them into a brood pouch. In this pouch she may carry up to 50 eggs. In approximately two months, the young roly-polies will emerge. They will look like small roly-poly bugs, and if it is a species that can roll, it will be able to do so at birth. The Michigan Entomological Society notes that these isopods will molt up to a dozen times in their lifetime, and the average lifespan of a roly-poly is between two and five years.
In Roly-polyology 101 by the National Park Service, it is noted that roly-polies have many unique adaptations. Roly-poly bugs cannot bite or sting and have an exoskeleton with plates. They like dark, moist areas and if left out in the sun they will perish. Many of the species are able to roll up into a ball for protection, but they can also use odor as a defense. They eat scat and decaying matter, including flesh. They are cold-blooded and react strongly to humidity levels, light and temperature changes. Animal specialist Julie Curl observed social behaviors such as fighting over food and communicating by tapping with their antennae. They absorb water with food, through mouth parts or by capillary action through their uropods.
Roly-poly bugs are decomposers. They digest material from dead plants and animals and waste products and return essential nutrients back into the soil. Because roly-polies are sensitive to changes in the environment, they are also used as biological indicators for the health of ecosystems. Additionally, roly-poly bugs are a food source for other animals.
Often these harmless creatures are considered pests. Because they seek out dark, cool places and are decomposers, they may be found in decaying organic matter and in gardens. Generally, they don’t eat the plants but have been known to cause some damage to tender plants and roots. University of California entomology professor Lester Ehler discovered that roly-poly bugs eat the eggs of stink bugs. Since stink bugs can do considerable damage to crops, roly-poly bugs may be beneficial as a natural insect control method.
- University of Michigan: Welcome to the Weird and Wonderful World of Woodlice
- University of Arizona: Isopod, Pillbug, Sow Bug Information
- Michigan State Entomological Society: Rearing and Experimenting With Isopods
- University of California, Davis: Humble Roly-Poly Bug Thwarts Stinks Bugs in Farms, Gardens
- University of Nebraska: Isopod Habitat Preference
- National Park Service: Roly-Polyology 101