Household invasion by several / dozens / hundreds / thousands / millions of millipedes (take your pick) is again a common problem across Iowa. Some background information may be useful.
Millipedes live outdoors in damp areas such as under leaves, needles and dead plant debris, or in cracks and crevices. They feed on damp and decaying vegetable matter and are beneficial as "recyclers" of organic matter. However, they become pests when they migrate into buildings as accidental invaders. They are most active at night and usually hide during the day in cracks and other moist locations.
Millipedes are harmless; they do not feed upon building structures or furnishings and they can not bite or sting. Millipedes can not reproduce indoors. All millipedes found inside wandered in by mistake.
Why so many?
Millipede populations have been favored by the wet weather of the past decade. More recently, the mild winter just past may have improved their survival. And finally, damp, warm weather so far this summer has favored the nocturnal migrations of these extraordinary populations. It adds up to a real mess for large numbers of home and business owners.
What to do?
Unfortunately, chemical control of millipedes is not easy nor is it certain. Residual insecticides applied outdoors (to reduce their numbers at the source or to prevent entry) are not terribly effective. Breeding sites may be a long distance from the building and will be difficult to treat because of the organic cover at the site. Still, residual insecticides such as Sevin, permethrin, Dursban, and diazinon can be applied in a 5- to 20-foot wide barrier around the building to reduce entry. Thorough application will aid in control, but reliance on chemical control alone is often unsatisfactory.
Cracks, gaps and other points of entry around windows and doors and in foundation walls should be sealed if possible. The indoor use of household insecticides provides little if any benefit. Millipedes that wander indoors usually die in a short time because of the dryness, and spraying cracks, crevices and room edges is not very useful. Sweeping or vacuuming up the invaders and discarding them is the most practical option.
This article originally appeared in the July 23, 1999 issue, p. 103.