Pillbugs and sowbugs
Pillbugs (family Armadillididae) and sowbugs (family Porcellionidae) are not insects or true bugs. They are soil-dwelling crustaceans in the order Isopoda (called isopods). They feed primarily on decaying plant material and occur mostly hidden under organic litter or other debris on the ground and beneath low-growing plant parts. They also chew fruit, succulent plant parts, seedlings, and vegetables that touch damp soil.
Pillbugs and sowbugs are distinguished from insects and other many-legged creatures by the adults having seven pairs of legs. Adult pillbugs and sowbugs have a small head and six small abdominal segments. They have seven relatively large thoracic segments, each having a pair of legs. Adult insects (and often immatures) on the other hand have three pairs of legs, while centipedes and millipedes have many more pairs of legs.
Pillbugs and sowbugs have a hard, shell-like covering that is made up of a series of segmented plates, a significant difference from the body segments of insects. The body of pillbugs and sowbugs are oblong to oval shaped with an arched or half-domed (convex) back. The top of sowbugs is more flattened in comparison with pillbugs. The adult body of both isopod types is about 1/3 to 3/4 inch long with antennae that are about one-quarter the body length.
The young (immatures) are pale yellow to whitish and about 1/12 inch long when they emerge from their mother's brood sac. Older individuals are brown to dark gray but may be blue or purplish if recently molted.
Males and females can be distinguished by examining their underside. Males have copulatory organs on the front underside of the thorax. Females lack these appendages and have a pouch on their underside through which when pregnant can be seen eggs or internally hatched young.
When disturbed, pillbugs commonly curl into a ball resembling a pill, hence their common name. Sowbugs cannot roll into a ball and commonly scurry away when disturbed. Pillbugs have a smooth rounded rear end. In comparison, sowbugs have distinct appendages protruding from their rear.
Eggs are retained in a brood sac on the underside of females. Eggs hatch about 1 month after being produced and the young remain in the brood sac for about 2 weeks before they emerge. The young pillbugs and sowbugs molt (shed their covering and grow a newer, larger covering) about every 1 to 2 weeks over a several month period as they grow into adults. Adults can live for 2 to 5 years.
Sowbugs and pillbugs feed primarily on decaying plant material and are important decomposers of organic matter. However, they occasionally feed on seedlings, new roots, lower leaves, and fruits or vegetables touching the soil. They sometimes come indoors, which can be nuisance.
If pillbugs or sowbugs are a problem, reduce the amount of decaying organic matter on soil and minimize wetness of the soil surface. Reduce the frequency of irrigation to the extent compatible with healthy plant growth. Irrigate early in the day so surfaces are drier by evening. Keep compost and mulch back from plants and building foundations. Using raised beds or planting boxes, plastic mulch instead of organic material, and drip or furrow irrigation instead of sprinklers usually keeps pillbugs and sowbugs from becoming serious problems. Black plastic mulch may be more effective at discouraging them than white or clear plastic.
Ways to stop these invertebrates from coming inside:
- Install weather stripping and door sweeps (bottom barriers).
- Keep irrigation water back from foundations especially near entranceways.
- Modify or reduce habitat around buildings that favors invaders, such as keep plants, mulch and other debris, and other hiding places at least several inches back from foundations and even further back from entranceways.
- Reduce outside lights’ attraction of invertebrates. For example, reduce brightness, switch to motion-activated security lights instead of always-on lights at night, and experiment with yellow or other-colored lighting.
- Seal or screen gaps and openings in buildings.
For more tips on stopping invertebrates from coming indoors see Integrated Pest Management Checklist for Early Care and Education Programs (PDF) from UC San Francisco.
For more information see Colorado Insects of Interest: Pillbug; Common Name: Pillbug, Roly-poly, Woodlouse, Scientific Name: Armadillidium vulgare (Latreille) (Malacostraca: Isopoda: Armadillidiidae); Pill Bug Biology: A Spider's Spinach, but a Biologist's Delight; and Pillbugs and Sowbugs, or Woodlice (Isopoda).
Adapted from the publications above and Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).