Homegrown: Millions of millipedes

Another pest question from a reader resulted in a quick answer from Donald Lewis, entomologist at Iowa State University.

Lewis is again hearing numerous reports about the household invasion of millipedes in Iowa.

The Homegrown reader described the pests invading her tackroom as little brown worms, almost an inch long, that curl up into a ball when you touch them and then crunch if you step on them. She sent along photos.

Here is the answer from Lewis: “These are very common and frequently abundant, but have been particularly numerous and annoying the past few years after several wet summers in a row.

“Millipedes are ecologically beneficial as ‘recyclers' in the ecosystem.  They live in damp locations where they feed on decaying organic matter.

“They are harmless and cannot damage property, crops, livestock, people or pets.  They wander long distances at night, especially on warm, damp or humid nights.  They vary greatly from place to place but are particularly numerous near CRP (“set-aside”) fields, retaining walls, and other places with lots of damp cracks, gaps and decaying organic matter.”

Millipedes are usually found in the garage, basement or lowest level, although they may wander into other parts of the house. They are most active at night and usually hide during the day in cracks and other moist locations. Lewis points out that millipedes do not feed upon building structures or furnishings and they cannot bite or sting.

Millipedes cannot reproduce indoors. All millipedes found inside wandered in by mistake.

Damp, warm weather favors the nocturnal migrations of these extraordinary populations, Lewis notes.

Chemical control of millipedes is not easy nor is it certain, he said.

According to Lewis, 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.

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.