by Michael F. Potter, Extension Entomologist
University of Kentucky College of Agriculture
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.
Recognition and Habits
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.
- Minimize Moisture, Remove Debris - Problems with these pests in Kentucky often coincides with excessively wet weather; patience and drier conditions often will correct the problem. The most effective, long-term measure for reducing entry of millipedes (and many other pests) is to minimize moisture and hiding places, especially near the foundation. Leaves, grass clippings, heavy accumulations of mulch, boards, stones, boxes, and similar items laying on the ground beside the foundation should be removed, since these often attract and harbor pests. Items that cannot be removed should be elevated off the ground.
Don't allow water to accumulate near the foundation or in the crawl space. Water should be diverted away from the foundation wall with properly functioning gutters, down spouts and splash blocks. Leaking faucets, water pipes and air conditioning units should be repaired, and lawn sprinklers should be adjusted to minimize puddling. Homes with poor drainage may need to have tiles or drains installed, or the ground sloped to so that surface water drains away from the building. Humidity in crawl spaces and basements should be reduced by providing adequate ventilation, sump pumps, polyethylene soil covers, etc.
Since millipedes often thrive in the moist, dense thatch layer of poorly maintained turf, de-thatching the lawn and keeping the grass mowed close should make the lawn less suitable for millipedes. Over-watering or watering during the evening may also contribute to millipede problems.
- Seal Pest Entry Points - Seal cracks and openings in the outside foundation wall, and around the bottoms of doors and basement windows. Install tight-fitting door sweeps or thresholds at the base of all exterior entry doors, and apply caulk along the bottom outside edge and sides of door thresholds. Seal expansion joints where outdoor patios, sunrooms and sidewalks abut the foundation. Expansion joints and gaps should also be scaled along the bottom of basement walls on the interior to reduce entry of pests and moisture from outdoors.
- Insecticides - Application of insecticides along baseboards and other interior living areas of the home are of little use in controlling millipedes. Most wandering millipedes which end up in kitchens, living rooms, etc. soon die from a lack of moisture. Removal with a vacuum or broom is all that is needed. Insecticides may help to reduce inward invasion of these and other pests when applied outdoors, along the bottom of exterior doors, around crawl space entrances, foundation vents and utility openings, and up underneath siding. It also may be useful to treat along the ground beside the foundation in mulch and ornamental plant beds, and a few feet up the base of the foundation wall. Heavy accumulations of mulch and leaf litter should first be raked back to expose pest hiding areas. Insecticide treatment may also be warranted along the interior foundation walls of damp crawl spaces and unfinished basements.
Various insecticides sold in hardware/lawn and garden shops are effective, including Sevin, Dursban, and synthetic pyrethroids (e.g., Spectracide Bug Stop, Ortho Home Defense System). Treatment can be accomplished with a compressed air "pump up" or hose end sprayer. Dust formulations (e.g., silica get, diatomaceous earth) also work well for treating cracks, weep holes, and similar openings in the foundation.
For more information about Millipedes, including pictures of common Kentucky Millipedes, visit the Kentucky Critter Files.
CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.
Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!