Centipedes and millipedes look similar at first glance, but they’re fundamentally different creatures with different body plans, diets, and behaviors. The fastest way to tell them apart: count the legs on a single body segment. Centipedes have one pair of legs per segment, while millipedes have two pairs per segment.
How to Tell Them Apart at a Glance
Body shape is the easiest visual cue. Centipedes have flat bodies with legs that stick out visibly to the sides, giving them a slightly spidery look. Millipedes have rounded, cylindrical bodies with a hard external skeleton, and their short legs tuck underneath so they’re less conspicuous.
Beyond shape, their leg arrangement is the defining anatomical difference. Each centipede body segment carries just one pair of legs. Millipede segments each carry two pairs. Most centipede species have between 15 and 30 pairs of legs total, while most millipedes have between 30 and 300 legs. Despite the name (“hundred legs” vs. “thousand legs”), neither creature literally hits those numbers. No known millipede species has exactly 1,000 legs, and centipedes always have an odd number of leg pairs, so they never land on exactly 100.
Speed and Movement
Centipedes are built for speed. Their flat bodies and long, prominent legs are adapted for running, and they can move surprisingly fast across floors, walls, and ceilings. House centipedes in particular are known for darting across surfaces at speeds that startle people. This quickness is central to how they survive: they’re active hunters that chase down prey.
Millipedes are the opposite. They move slowly and deliberately, their many short legs creating a wave-like ripple as they walk. When threatened, most millipedes curl into a tight spiral rather than fleeing. Their survival strategy is chemical defense, not escape.
What They Eat
This is where the two creatures diverge most sharply. Centipedes are carnivores. They actively hunt insects, spiders, silverfish, and even small cockroaches, killing prey with venomous fangs located just behind the head. If you find a centipede in your home, it’s likely hunting other bugs that are already there.
Millipedes are detritivores, meaning they feed on decaying organic matter. Their diet consists mostly of decomposing leaves, rotting wood, and other dead plant material. This makes them valuable contributors to soil health: they break down leaf litter and cycle nutrients back into the ecosystem. They’ll occasionally nibble on living plant material, but only when it’s already starting to decay. They have no venom and no fangs.
Bites, Stings, and Skin Reactions
Centipedes can bite, and larger species deliver a painful one. The bite causes localized swelling and redness, but symptoms rarely last more than 48 hours. Placing an ice cube wrapped in a thin cloth on the bite typically relieves the pain. For most people, a centipede bite is unpleasant but not dangerous.
Millipedes don’t bite at all. They can, however, secrete a defensive toxin when handled or disturbed. This fluid causes burning and itching on skin contact. If you accidentally rub it into your eyes, it can cause redness, swelling, and significant pain. Wash affected skin thoroughly with soap and water. Eye exposure should be flushed immediately with water. Some millipede species also release an offensive odor when disturbed, and their secretions can stain fabrics.
Where You’ll Find Them
Both creatures prefer damp, dark environments. Outdoors, you’ll find them under rocks, logs, mulch, and leaf piles. They’re most active at night. Indoors, they gravitate toward basements, bathrooms, and anywhere moisture collects.
The reasons they end up inside differ, though. Centipedes come indoors to hunt. If you’re seeing centipedes regularly, you likely have a population of smaller insects they’re feeding on. Millipedes wander inside by accident, often during heavy rain or in fall when outdoor conditions change. They don’t reproduce or feed indoors and typically die within a few days of entering a home.
Keeping Them Out of Your Home
Since millipedes can’t survive indoors for long, killing the ones you see doesn’t solve the problem. More will simply wander in from their outdoor breeding sites. The most effective approach is physical exclusion: install weather stripping on doors, caulk around window and door frames, and seal cracks behind baseboards. A wet/dry vacuum or broom and dustpan is the fastest way to remove the ones already inside. Place them in a sealed plastic bag and throw them in an outdoor trash container.
If millipedes keep appearing in large numbers despite sealing entry points, a perimeter treatment around the foundation can help. Diatomaceous earth is one option that doesn’t involve synthetic chemicals. For heavier infestations, residual insecticides can be applied in a band around the home’s perimeter and at entry points like cracks, weep holes, vents, and pipe penetrations. Raking back thick mulch before treating exposes the soil where millipedes breed.
For centipedes, the best long-term strategy is reducing the prey insects they’re hunting. Fix moisture problems (leaky pipes, poor ventilation in crawl spaces, standing water) to make your home less attractive to both centipedes and the bugs they eat. Reducing clutter in basements and storage areas removes hiding spots.
Quick Comparison
- Legs per segment: Centipedes have one pair; millipedes have two pairs
- Body shape: Centipedes are flat; millipedes are rounded
- Speed: Centipedes are fast runners; millipedes are slow and curl up when threatened
- Diet: Centipedes are predators; millipedes eat decaying plant matter
- Danger to humans: Centipedes can deliver a painful bite; millipedes secrete an irritating fluid but don’t bite
- Why they’re indoors: Centipedes are hunting prey; millipedes wandered in by accident
- Indoor survival: Centipedes can live and breed indoors; millipedes die within days