Occasionally millipedes, sowbugs, pillbugs and centipedes may be found in moist areas of the home, in rotting wood or under piles of moist debris in basements, near patio doors and in garages. None of them are true insects, but they belong to the class Crustacea, a closely related group of arthropods. Centipedes, sowbugs, pillbugs and millipedes are all primarily nocturnal, avoiding light. They are fairly common out-of-doors and may be seen near foundation walls, under logs, in piles of leaves and in gardens. Occasionally large numbers of millipedes leave the soil and crawl onto and into (if there are openings through which they can enter) houses where they may be an extreme nuisance to home dwellers. In a few instances invasions have been noted after periods of extremely wet weather and persist for a few weeks or until cold weather occurs.

Millipedes:

Millipedes ("thousand leggers") have elongated, segmented worm-like bodies with short antennae and two pairs of short legs per body segment. There are many species of millipedes, but the ones that commonly invade homes are usually 12-40 mm (1/2 to 1-1/2 inch) long, brown or black, and curl up when disturbed. They crawl slowly across the ground and, when disturbed, roll themselves into a coil. A few species which occur in wooded areas, however, may exceed 10 cm (4 inches) in length. Millipedes deposit eggs in clusters in the soil throughout the summer. Young hatch from the eggs and undergo a series of molts, during which the number of segments is increased. It often takes more than one year to reach sexual maturity. Occasionally millipedes will attack the stems and roots of young plants, or they may feed on tubers or vegetables stored in cellars or basements. Such damage, however, most frequently occurs in the presence of previous damage, as millipedes customarily feed on decaying vegetation.

Millipede. Photo from the Department of Entomology, University of Minnesota Extension Service

Sowbugs & Pillbugs:

Sowbugs and pillbugs are oval, dark-gray, hard shelled arthropods with seven pairs of legs. They reach about 12 mm (1/2 inch) in length. They are also found in moist places, under debris or in damp soil where decaying vegetation provides food and, like millipedes, they can cause some damage to young plants. When disturbed, pillbugs can roll themselves into a ball, but sowbugs cannot. The females of sowbugs and pillbugs carry the young in a pouch on the underside of her body until the young leave the pouch. They may have two or more broods per year. Sowbugs often live to be two years old.

Sowbug (left) and Pillbug (right). Photos from the University of Florida Cooperative Extension

Centipedes:

Centipedes ("hundred-leggers") are elongated, short-legged, flattened arthropods with 15 or more pairs of legs. Centipedes are gray to light brown and about 25-50 mm (1-2 inches) in length. There is one long pair of legs per body segment and the antennae are prominent. When disturbed, centipedes often run for cover, moving much more rapidly than millipedes. Centipedes can deliver a somewhat painful, venomous bite and should be handled with appropriate care. These arthropods are not likely to infest houses unless conditions are quite moist and prey is abundant. Centipedes are predaceous, feeding on insects, spiders and other small animals. They do not cause damage to plants.

Centipede Photoby Jeff Hahn, University of Minnesota Extension Service

Management--Preventing Invasion:

The heaviest migrations usually come from nearby wooded areas. Removing piles of rocks, boards, leaves, compost, and general refuse from around buildings will help reduce millipede, sowbug, and pillbug numbers. To keep these pests out of the home, foundation walls should be repaired, and any cracks around doors, basement windows or similar openings should be sealed with caulking compound. Correcting the conditions that might lead to excess moisture indoors is the most effective long-term solution. A good first step towards controlling the household centipede is to eliminate the presence of insects or spiders on which they may be feeding.

Outdoor Spraying:

Some species of millipedes, sowbugs, and pillbugs are difficult to kill with any insecticide. Select only formulations of these insecticides labeled for millipede, sowbug and pillbug control and follow label directions closely. Apply the spray to any infested area outdoors and as a barrier treatment on foundation walls and soil adjacent to the buildings. Use enough to thoroughly wet the surface being treated and any visible millipedes, sowbugs or pillbugs. Repeat applications may be needed if these creatures continue to move in from surrounding areas.

Indoor Control Measures:

Any millipedes, sowbugs or pillbugs that are found indoors can be eliminated by hand collection, vacuuming or otherwise sweeping them up. Centipedes may be killed by squashing with a gloved hand (remember, they can bite) or any makeshift "swatter."

Adapted from the Cornell Cooperative Extension and the Purdue University Cooperative Extension Service, 1999