Joseph Berger, Bugwood.org
Millipedes are many segmented, wormlike arthropods found throughout Pennsylvania. They usually go unnoticed under leaves, rocks, boards and other locations that provide a cool, damp habitat. Occasionally, millipedes may enter structures in great numbers causing alarm. Fortunately, they do no damage (other than being a nuisance) and cannot long survive the dry atmosphere found within most buildings.
Millipedes can be easily identified by their two pairs of legs per body segment (except for the first three segments that have one pair each). Because of the many legs, they are often called 'thousand-leggers'. Sometimes they are called 'wire worms' because of their cylindrical wire-like body shape. However, they should not be confused with the beetle larvae known as wireworms (family Elateridae: the click beetles) which have only six legs, feed on grass roots, are typically a dark yellow color and will not crawl about on the soil surface. Most of the millipedes that people come in contact with are a dark brown color, approximately an inch long and one sixteenth of an inch in diameter.
Most have a hard outer skin and will curl into a spiral upon death.
Millipedes normally live in cool, damp places such as those found under stones, leaf mold, mulch, compost heaps, piles of grass clippings, and brick pathways. At certain times of the year millipedes become restless and migrate from their normal living places; they appear in window wells, basements, garages and other places where they become an annoyance. These migrations are often associated with cooler weather or following heavy rains, but may also be a function of mating behavior, especially if the millipedes are seen to climb trees, fences, buildings and the like to a height of approximately six feet.
Before millipedes gain access to the structure
It is preferable to locate the source(s) of the infestation and make modifications that are unattractive to millipedes. Some of the places mentioned above should be investigated and removed, or treated with a pesticide labeled for lawn and soil applications. Piles of compost or grass clippings, leaf mold around shrubbery and house foundations are likely spots for infestations to continue breeding. Some home foundations have a border of river gravel or other mulching over a blanket of plastic sheeting or similar weed prevention barriers. Millipedes will thrive under these conditions and treatment of the mulching with a pesticide will not be effective, as the pesticide will not penetrate the plastic. Removal of the weed barriers will reduce the soil moisture and increase the temperature - both which are unattractive to millipedes - and allow pesticides to reach the millipedes.
After millipedes enter the structure
Since millipedes do not live for more than a few days indoors, treatment inside the home is not necessary. Vacuum or sweep millipedes into a dust pan for removal.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Authored by: Steven B. Jacobs, Sr. Extension Associate
Reviewed January 2013