Irene Shonle, Director CSU Extension in Gilpin County.  Both millipedes and centipedes sometimes come into houses in the fall, and I’ve recently heard from a few people finding these creatures inside their homes.

Although they look superficially similar, millipedes and centipedes are actually quite distinct, coming from entirely different classes of arthropods (Diplopoda and Chilopoda, respectively). Centipedes are hunters, preying on small insects, while millipedes are scavengers, feeding primarily on decaying plant material.  The easiest way to distinguish them is to look at the number of legs per segment – centipedes have only 1 pair of legs (often quite long), and millipedes have two short legs.  Centipedes are also much faster, and are rare in the mountains.

Millipedes are worm-like creatures with a rounded-to-slightly-flattened body made up of segmented plates. The most common millipedes are dark brown and reach 1 to 1 1/2 inches when full grown. A common description is “little black worms crawling in the basement windows.” They will come into houses through tiny gaps, looking for protection and moisture. Despite having a hard body covering, they lack the waxy protective layer of insects and are very sensitive to desiccation. Their usual strategy is to tunnel to find adequate moisture below ground. They are important in the decay process and in nutrient cycling.

In general, the distribution of millipede species in Colorado is poorly known. In addition to the ones we see in houses and gardens, we might also find the more unusual-looking Duff millipedes. These are found in forested areas, live on or under bark and feed on fungi and lichens. They only occasionally invade houses.

Centipedes also live in moist areas and are just as prone to drying out as the millipedes (which can lead to home invasions).  They tend to hunt at night, attacking their prey with curved jaws and injecting them with venom.  Although they are poisonous and can deliver a painful bite to humans, they are not life-threatening, and only the largest species can even break human skin.  There are about 25 species of centipedes in Colorado

Some, such as the house centipede, live almost exclusively in houses, feeding on spiders, flies and other house insects. Their long legs allow the house centipede to run quickly. When exposed in a darkened room by switching on a light they rapidly scurry for cover.

Sometimes they move in the direction of the human, an action that may be misinterpreted as an “attack”. In reality, with their poor vision and chemical senses, any movement towards a person is either random or done because the person is perceived as a large mass that can provide cover. House centipedes are not aggressive and will bite only if physically confined. The bites are reportedly mildly painful.

In general, neither of these insects are really considered nuisance pests.  Because they cause no damage in homes other than a minor annoyance, the best way to handle infestations is to wait a few days for the problem to subside, then vacuum the bodies that remain. Remove debris and other favorable habitats from around building foundations and control moisture. Seal or caulk openings around the foundation to reduce future problems.

The CSU Gilpin County Extension Office is located at the Exhibit Barn, 230 Norton Drive, Black Hawk, CO 80422, 303-582-9106, www.extension.colostate.edu/gilpin. Colorado State University Extension provides unbiased, research-based information about, horticulture, natural resources, and 4-H youth development. Colorado State University Extension is dedicated to serving all people on an equal and nondiscriminatory basis.