The multi-legged, worm-like creatures that are often found under decaying logs outdoors—or occasionally indoors under moist boxes, in rotting wood framing, or under piles of moist newspapers—are arthropods from the Diplopoda and Chilopoda classes of creatures. They belong to the Myriapoda subphylum, a group that comprises multi-legged species of various types. Although often grouped together with insects, millipedes and centipedes are arthropods that are categorically different than insects (which have six legs) and arachnids (which have eight legs).
Centipedes and millipedes are primarily outdoor creatures that subsist on decaying plant material (millipedes) or small insects and other creatures (centipedes). Neither of these creatures causes damage or disease, nor do they nest and breed indoors. If you find them indoors, it is usually because they've simply wandered in from a nearby woody environment. They do not damage food, plants, furniture, or buildings as other more harmful pests do, such as cockroaches, rodents, and flies.
Because they require moisture and foods such as organic material or insects to survive, millipedes and centipedes do not live for long or reproduce in homes, as the conditions are generally too dry. Still, the reaction to finding millipedes and centipedes in your home is often one of revulsion, and most people wish to get rid of them and prevent others from finding their way in.
Ways to Get Rid of Millipedes and Centipedes
Move Them Outdoors
If you aren't squeamish about handling the live bugs, scoop up millipedes and centipedes on a sheet of paper or in a cup, then release them outdoors in a wooded area where they can conduct their normal (and beneficial) habits of eating decaying plant material or feasting on small insects.
Kill Them Manually
If centipedes or millipedes are found in the house, you can simply vacuum or sweep up or crush the bugs. These are not creatures that nest or colonize indoors, so killing them when you find occasionally find them is a perfectly good strategy for successful control.
What About Pesticides?
For all but exceptional cases of massive numbers of invading pests, indoor pesticide use is not recommended.
What Causes Millipedes and Centipedes?
These creatures crave moisture, and when they move indoors through cracks in foundations and around ground-level windows, it is usually when outdoor conditions have become hot and dry. Once indoors, millipedes and centipedes often hide in cracks and crevices over winter, emerging in spring.
How to Prevent Millipedes and Centipedes
Preventing millipedes and centipedes indoors is best accomplished by diligent sealing all cracks, holes, and gaps in foundations and keeping window and door frames and sill plates in good repair and properly weather-sealed. Keeping outdoor areas around the house free of leaf litter and brush will reduce outdoor populations. Allow the ground around foundations to dry out thoroughly between waterings of plants and shrubs.
Indoors, use a dehumidifier to keep air dry, and keep cardboard boxes and other organic materials up away from concrete slabs and floors.
If outdoor infestations are severe, you can apply a band of pesticide around the foundation to discourage these bugs from seeking entry into your home. A granular form of deltamethrin, lambda-cyhalothrin, or permethrin works well for this.
Millipedes vs. Centipedes
Millipedes and centipedes are often confused for one another, but there are distinct differences between these arthropods:
|Size||Up to 1 1/2 inches, rarely up to 4 inches||1/4 inch to 6 inches|
|Legs||Two pairs per body segment||One pair per body segment|
|Color||Brown to black||Yellow to dark brown|
|Body shape||Rounded body||Flattened body|
|Food||Decaying organic material, occasionally living plants||Small insects, spiders, worms, snails|
|Movement||Curl up when disturbed||Scurry quickly to dark hiding places|
Can millipedes or centipedes be kept as pets?
Giant African millipedes, a relative of the much smaller North American millipede species, are sometimes kept as pets. These arthropods grow 7 to 11 inches in length and are so docile that they are readily handled. There are also large species of centipedes that are sometimes kept as pets, but because centipedes are carnivores with biting jaws, the larger varieties carry the potential for biting. Thus, large centipedes are usually not handled if they are kept as pets. Millipedes and centipedes are relatively easy to care for in terrariums. They require moist, dark hiding places and readily feed on dead plant material or bugs, depending on the species.
Do millipedes and centipedes serve any useful functions?
It can be argued that all creatures, even those generally regarded as pests by humans, serve valuable ecological functions. In the case of millipedes, these creatures help in the breakdown and consumption of decaying plant material. It is creatures such as millipedes that cause dead stumps and other plant debris to gradually vanish rather than pile up. Centipedes are carnivores that consume many harmful insects and other small creatures in the landscape. Both millipedes and centipedes add nutrients to the soil through their excrement. When found outdoors in the garden, there is no reason to try to eliminate these arthropods. Indeed, they are a sign of a healthy outdoor ecosystem. It's only when they stray indoors that control measures may become necessary.
Do centipedes or millipedes bite?
Centipedes of the U.S. rarely bite, but when they do, the affected area can redden and swell similar to a bee sting. In other areas of the world where centipedes are often larger, their bite can cause burning pain. Millipedes bite only very rarely; when they do, mild allergic reactions can sometimes occur.
Holt, Jack R., and Carlos A. Iudica. "Description of The Subphylum Myriapoda (Latrielle 1802)." Diversity Of Life, 2015.
Bechinski, Edward John, and Frank W. Merickel. "Homeowner Guide to Centipedes and Millipedes." University of Idaho Extension, 2009.