The "millipede migration" that has caused considerable concern for the past 3 - 4 years continues this spring. Wet weather for the past several summers has favored these beneficial, organic matter recyclers to the point they are a major nuisance to many homeowners.
Millipedes live outdoors in damp areas such as under leaves, in cracks and crevices and under mulch around outdoor plantings where they feed on damp and decaying vegetable matter. They are most active at night and usually hide during the day. Most are 1 to 1 1/4 inch long with a very slender cylindrical shape and dark brown color. They characteristically coil into a spiral when handled or when they die in the corner of the basement. The typical millipede has approximately 160 very short legs on the entire length of the body underside.
Millipedes only become a pest when they move indoors as accidental invaders. They do not feed upon building structures or furnishings, they can not bite or sting and they do not reproduce inside the house.
Millipedes found inside wandered in by mistake, and controls should be aimed at keeping them outdoors or reducing their numbers at the source. Cracks, gaps and other points of entry around windows and doors and in foundation walls should be sealed if possible. Removing organic matter such as plant mulch and dead leaves from against the house may help achieve control. Also, damp conditions around the house foundation should be eliminated.
Insecticides are of limited benefit in controlling millipedes because of the protected areas where millipedes originate. In warm weather when millipedes are actively wandering, residual insecticides such as Sevin, malathion, Baygon, Dursban, and diazinon can be applied as sprays in a 5- to 20-foot wide barrier around the building to reduce entry. The moist areas where the millipedes originate must be sprayed and the control treatments must be thoroughly applied in such a way as to get the insecticide down to the soil surface.
Indoors, the use of residual insecticides such as "ant and roach killer" or "home pest control" is not very effective. However, since the millipedes that wander in usually die in a short time (because of the dryness), spraying is not practical. Sweep or vacuum up the invaders and discard.
This article originally appeared in the May 12, 1995 issue, p. 67.