Just like last year, this hits home for me because I am having this problem myself. Those who live next to woods will typically have them worse because they come in large numbers from the duff in the woods.
Millipedes will not cause any harm. They are basically just a nuisance, even when they come inside your home. They do not bite, sting, or transmit diseases, nor do they infest food, clothing, or dry, structurally sound wood.
There are several species of millipedes that vary in both size and color, but the most common species that invades buildings is the “garden millipede”, which is brownish-black in color and about one inch long. Although millipedes are often called “thousandleggers”, they actually have far fewer legs but each body segment has two pairs of very short legs. When disturbed, millipedes often curl up into a “C” shape and remain motionless. They crawl slowly and protect themselves by secreting a cyanide-like compound that has an unpleasant odor. Some people confuse millipedes with centipedes, which look somewhat similar. Centipedes have only one pair of legs per body segment and the legs are longer than those on millipedes. Centipedes also move about much quicker than millipedes.
Millipedes pass through the winter primarily as adults and lay their eggs in the soil in the spring. Millipedes are naturally attracted to dark, cool, moist environments that are rich in organic matter such as compost piles, heavily mulched shrub or flower beds, rotting logs, the soil under logs and stones, or as I mentioned earlier, in all that rotting leaf litter in the woods. They normally go unnoticed because they live in these relatively hidden habitats. Millipedes are scavengers, feeding primarily on decomposing vegetation. Major nuisance problems typically occur when the conditions become too hot and dry and the millipedes move to find moisture, or in this case, when it’s too wet and saturated soils force them to the surface and higher ground.
Millipedes might also migrate in the fall, presumably in the search of overwintering sites. All of these activities result in millipedes invading crawl spaces, basements and other areas of buildings. Common points of entry include door thresholds (especially at the base of sliding glass doors and garage doors), expansion joints, and through the voids of concrete block walls. Frequent indoor sightings usually means that there are large numbers breeding outdoors.
Fortunately, millipedes don’t survive indoors more than a couple of days (more likely just a few hours) because they can’t find suitable moist conditions. So most that you may find indoors may be already curled up and dead.
When you find them crawling inside, use a piece of toilet paper, tissue, or paper towel to pick them up to avoid getting the unpleasant odor on your hand. Crush them, then throw them in the trash or flush them down the toilet. Remove the dead ones the same way or use a vacuum cleaner or broom.
For control of these unwanted pests, the use of pesticides is typically a short-term solution to a potentially long-term problem. Your main emphasis should be first placed on reducing conditions and access points favorable to millipede invasions.
As I said earlier, if you live by the woods there is not a lot you can do. You can create an insecticide barrier from the woods, but again, this is only a short term solution. Until we return to drier conditions you can do few things around your house to discourage them. Eliminate trash piles, rocks, boards, leaf piles and similar materials from the immediate vicinity around the house.
If there is mulch around the foundation of your house, don’t let it get too thick and pull it back a few inches from the foundation to create a small dry area that they don’t like to cross. You might also treat the mulched area with an insecticide. Most any insecticide will work such as those containing bifenthrin, cyfluthrin, lamda-cyhalothrin, permethrin, carbaryl (Sevin), etc.
Prevent water from accumulating near the foundation, in basement walls, or in the crawl space. Keep gutters and downspouts free of debris and use either splash guards or perforated pipe to reduce puddling. Homes with poor drainage might need to have foundation drains installed or at least the surrounding ground contoured or sloped to redirect surface water away from the foundation.
Reduce the humidity in crawl spaces and basements by providing adequate ventilation, sump pumps, polyethylene soil covers, dehumidifiers, etc.
Physically exclude millipedes from entering the home where possible. Make sure doors and windows fit tightly and caulk cracks and crevices that permit their entry to the inside.
REACH SID MULLIS, THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE FOR RICHMOND COUNTY, AT (706) 821-2349 OR SMULLIS@UGA.EDU.