Each year I get samples of millipedes that are invading houses and other structures. The following is an article on the subject. Commercial landscape companies may be asked to deal with the problem.
Millipedes are long, many segmented creatures that use their two pairs of legs per body segment to move along with deliberate speed. There are several species in Delaware with a variety of shapes and colors.
Millipedes can be very abundant in forest litter, grass, thatch, and in mulched areas. These places provide needed food, shelter, and dampness. Usually, millipedes stay out of sight unless abundant rainfall or some other event, such as the mating season, puts them on the move.
While harmless and in fact, helpful recyclers, millipedes generally are not welcomed with enthusiasm. They 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 mean 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 usually do not survive indoors for more than a few days.
Minimize moisture & remove hiding places - The most effective, long-term measure for reducing entry of millipedes is to minimize moisture and hiding places, especially near the foundation. Leaves, grass clippings, heavy accumulations of mulch, boards, stones, boxes, stacked firewood or 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.
Seal 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 - Exterior applications, in the form of barrier sprays, may help to reduce inward invasion 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. There is no benefit from treating indoors.
One species of millipede. Photo by Gary Alpert, Harvard University, Bugwood.org.
Adapted from "Millipedes and Wood Cockroaches - Common Invaders in July" By Lee Townsend in the current edition of the Kentucky Pest News http://www.uky.edu/Ag/kpn/kpn_09/pn_090714.html