Centipedes And Millipedes

By Therese Ciesinski, GardenSMART

People often confuse centipedes and millipedes, however they are two different species. What they have in common are long bodies, lots of legs and the tendency to wander into our homes when the climate outdoors becomes too uncomfortable for them. Here’s how to tell the difference between the two and what to do if you see them inside your house.

Millipede. Photograph by Joseph Berger, Bugwood.org.

Millipedes

There are two millipede species homeowners and gardeners are most likely to encounter. The first is the common millipede. An inch long and brown-black, it looks a bit like a worm perched on dozens of tiny legs. The other is the lighter-colored garden millipede, which has a flatter body. You might find this one in the soil of your houseplants.

The prefix “milli” means thousands, and their nickname is thousandlegger. While one may look like it has a thousand legs, there are only two per body segment (which on longer millipedes still means there can be 400 legs).

Millipedes like it moist and cool. Outdoors, they hang out in organic material such as rotting logs, plant debris, and in cracks and crevices, and are more active at night. Like their sowbug relatives they’re one of the army of creatures that’s considered beneficial because they break down organic matter and help to create humus.

Greenhouse millipede. Photograph by Joseph Berger, Bugwood.org.

If you see them indoors, it will be in damp places such as basements, garages, or bathrooms. They are slow movers, and curl into a “c” shape when disturbed or dead.

Millipedes overwinter as adults, but don’t reproduce indoors. The one that surprises you in your bathroom in the middle of the night has wandered in by mistake and isn’t starting a family. The heat and low humidity indoors in the winter means millipedes don’t live long in the average house, anyway.

Millipedes are harmless: They don’t carry disease, don’t bite or sting, don’t infest grains or food, and won’t destroy anything in your house.

Photograph by Dilcoe at English Wikipedia, public domain, via Wikimedia Commons.

Centipedes

Centipedes are about an inch or so long, with flattened bodies that can be a grayish-yellow or brown. Sometimes they are striped. They have more prominent antennae than millipedes and one set of jointed legs per body segment. Centipede legs are long, making them look larger than they are. They are fast movers, much faster than millipedes and can climb walls and ceilings.

Outdoors, centipedes also live in organic matter: under stones, bark, mulch, or leaves. They are carnivores, eating spiders, sowbugs, and yes, millipedes. Their jaws contain a venom that kills their prey.

Centipedes can bite humans, but in most species their jaws are too small to pierce skin. Larger species can give a painful bite which can cause swelling and an allergic reaction, particularly in people allergic to bee or wasp stings. Of the over 3500 species of centipede world-wide, however, only 15 species are dangerous to humans.

Photograph by Lightnen, public domain, via Wikimedia Commons.

Both centipedes and millipedes are seen most frequently in spring and summer when they come inside looking for moist, dark places to hide when the weather outside is hot and dry.

Since they pose little threat to people, there’s rarely a point in breaking out the pesticides, because there usually aren’t enough of either insect to merit that kind of level of control.

To keep millipedes and centipedes from getting in, seal cracks around doors and windows and in the basement or house foundation. Keep organic material away from the sides of the house. Running dehumidifiers in any damp areas of your home will also discourage them.

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