By Donald R. Lewis
Iowa State University Extension
They are called “worms,” “wireworms,” “armyworms” and names that are not repeatable, but the pest is always the same -- millipedes. And usually not one millipede, but hoards, hundreds, thousands or millions of millipedes.
Millipedes are long, slender, wormlike animals with 4 legs on each of most body segments. Most millipedes have at least 60 legs and in the case of the common, inch–long millipede found in most landscapes and houses, each individual has 160 legs. But not many people notice the legs because they are small and tucked beneath the body. What you do notice about millipedes is their size (1 to 1/14 inch) their color (very dark brown), their shiny, hard shell (crunchy), their long, cylindrical shape and their habit of curling into a coil when disturbed, handled or when they are dead.
Good News, Bad News
Millipedes are harmless. They can not bite or sting and they do not feed on structures, furnishings or landscape plants. They do feed on damp and decaying plant material and are ecologically beneficial as “recyclers” of organic matter. They live outdoors in damp areas such as under leaves, needles, plant debris, mulch and similar habitats.
The bad news is millipedes often embark on mass migrations, especially on humid, warm nights in the fall and spring, during which time they wander into garages, basements and other parts of the house. All millipedes found inside have strayed in by mistake from breeding sites in the vicinity. Millipedes can not reproduce indoors.
Millipedes are most active at night. They wander out from their damp hiding places and roam aimlessly, often covering large distances with their slow, steady crawl. They are not drawn to garages and houses nor are they searching for anything in particular (food, warmth, mates, etc.).
Wandering millipedes eventually bump into the house where they find small gaps or cracks. They crawl into these small openings as a shelter from the dryness of the coming daytime. Millipedes hide during the day under the bottom edge of the garage door, in cracks along the house, sidewalk or driveway and in gaps in the foundation. Openings in the foundation allow the millipedes to enter the house, where they continue wandering until they find a place to hide or until they expire from lack of moisture, coiled in the corners of a room.
Discussing control options for millipedes is a frustrating exercise in listing what doesn’t work. As much as possible millipede control should aim at keeping them outdoors. Cracks, gaps and other points of entry around windows and doors and in foundation walls should be sealed as much as possible. Unfortunately, we know this is not complete protection because even brand new, energy efficient homes have millipedes.
Reducing their numbers outside at the source by removing organic matter such as plant mulch and dead leaves from against the house may help. Damp conditions around the house foundation should be corrected but since millipedes may be coming from dozens of yards away, changes on your property may not make any difference.
Insecticides are of very limited benefit in controlling millipedes because of the protected areas where they originate and because of the long distances they migrate. Some sources of millipedes such as woodlands and crop reserve program fields can produce unbelievably large numbers of millipedes that invade from distances of 50 feet or more. Spraying on and along the foundation usually has little effect, if any.
Thorough spray application to areas where the millipedes originate, using immoderate amounts of insecticide may aid in control by reducing populations. However, reliance on chemical control is usually unsatisfactory.
The indoor use of household insecticides also 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. The best solution may be to learn to live with them until cold weather when they will become dormant –– at least until spring.