When I stepped into our laundry room this morning, I found dozens of thousand legger worms curled up on the floor. Some were dead. I realize that they must have come in under the basement door, but we’ve never had this problem before. Why now?

W. L., Everett, MA

Your “thousand-leggers” are better known as millipedes and we get calls about them whenever there is a change in outdoor conditions: too wet, too dry, too hot. These arthropods (they’re not worms and they’re not insects) live outside in damp conditions such as under mulch or leaf litter, in grass clippings, or under logs or stones. They feed on decaying vegetation and remain pretty much hidden outside.

Millipedes Need Damp Conditions to Survive

But at certain times of the year and under certain conditions, millipedes will migrate looking for a more suitable environment. What they don’t realize, however, is that the inside of a home or other building is not suitable for them at all. As you’ve noticed, they usually don’t survive long once they are inside. They gravitate to the dampest parts of the home—usually the lower level, laundry rooms, garages, utility rooms, in crawlspaces, or near floor drains or sump pumps. Even these areas are not damp enough for long-term survival. Drying out these damp areas in your home will hasten their demise.

You may have migrating millipedes now because conditions have changed around the outside of your home, leading to a population explosion. Millipedes can build up to high numbers when there is a lot of rotting vegetation like decaying leaves, grass, or compost, and when lawns are heavily watered which keeps vegetation and mulch constantly damp.

What Can You Do to Keep Millipedes Out?

Because millipedes die pretty quickly once inside, we don’t usually use insecticides indoors. Because they’re very docile, picking them up with a vacuum or broom and dustpan works well. Instead, we concentrate our control efforts on the outside of your home, stopping millipedes at the foundation before they have a chance to get inside. There are two ways to do this: (1) blocking them by sealing openings that they use to enter, and (2) by having an exterminator treat the exterior perimeter of your home with insecticide. At Colonial Pest, we offer both pest exclusion methods and a Preventative Maintenance Program that will eliminate millipedes and other pests around the foundation (see Managing Millipedes).

Millipedes may be an annoying presence temporarily but they don’t bite and they don’t do any damage inside. They can excrete a strong-smelling defensive fluid when handled, though. And for the record, they don’t have a thousand legs, more like 30 to 90, depending on the species.