Millipedes, often referred to as “thousand-leggers,” are commonplace around structures. They occasionally become pests when they migrate into buildings from their usual habitat outdoors. While millipedes sometimes enter in large numbers, they do not bite, sting, or transmit diseases, nor do they infest food, clothing or wood. They are simply a nuisance by their presence.
Most millipedes are brownish or blackish, wormlike, segmented and slow moving. Each body segment has two pairs of very short legs. Millipedes that commonly invade buildings are about 1/4 – 1 inch long and tend to coil up like a watch spring when disturbed. They do not bite, unlike some centipedes which have one pair of legs per body segment and tend to be faster moving.
In nature millipedes are scavengers and feed mainly on decaying organic matter. They occasionally feed on young plants but the damage inflicted is seldom significant. Millipedes have high moisture requirements and tend to remain hidden under objects during the day.
Around buildings they are common under mulch, leaf litter, compost, boards, stones, flower pots, and other items resting on damp ground. Another frequent hiding place is behind the grass edge adjoining sidewalks and foundations. Adult females lay up to a few hundred eggs in soil, leaf litter, etc., and the immatures pass through a series of molts, gradually increasing in size.
Millipedes often leave their natural habitats at night and crawl about over sidewalks, patios, and foundations. At certain times of the year, especially during autumn, they may migrate into buildings in great numbers. Fall movement into structures appears to be accidental, occurring in the course of searching for humid overwintering sites. Migration into buildings also is common during spring and summer, in conjunction with periods of excessively wet or dry weather.
Millipedes often invade crawl spaces, damp basements and first floors of houses at ground level. Common points of entry include door thresholds (especially at the base of sliding glass doors), expansion joints, and through the voids of concrete block walls. Frequent sightings of these pests indoors usually means that there are large numbers breeding on the outside in the lawn, or beneath mulch, leaf litter or debris close to the foundation. Because of their moisture requirement, they do not survive indoors more than a few days unless there are very moist or damp conditions.