That fast-moving, many-legged bug you spotted in your house is almost certainly a house centipede. It’s the most common multi-legged creature found indoors, with 30 long, spindly legs that make it look far more alarming than it actually is. The other possibility is a millipede, a slower, rounder creature that curls up when disturbed. Both are harmless to people, and neither one damages your home.
House Centipede: The Most Likely Culprit
The house centipede is yellowish-gray with three dark stripes running down its back. Its body is only about one to one and a half inches long, but those dramatically long legs (especially the rear pair on females, which can be nearly twice the body length) make it appear three to four inches from end to end. The legs are banded light and dark, giving the whole creature a feathery, almost eyelash-like look as it races across your wall or bathroom floor.
Adults have exactly 15 pairs of legs, totaling 30. That number isn’t random. House centipedes start life with just four pairs and add more with each molt, progressing through 5, 7, 9, 11, and 13 pairs before reaching the adult count of 15. So if you see a smaller one with fewer legs, it’s a younger version of the same creature.
They’re nocturnal hunters and impressively fast. You’ll most often spot them darting along baseboards, across bathroom ceilings, or near floor drains. They prefer dark, quiet spaces and will freeze or bolt when a light flips on.
How to Tell a Centipede From a Millipede
If the bug you found was slow, round-bodied, and curled into a tight spiral when you touched it, you’re looking at a millipede instead. The differences are easy to spot once you know what to look for.
- Body shape: Centipedes are flat. Millipedes are cylindrical, like a tiny tube.
- Legs per segment: Centipedes have one pair of legs per body segment. Millipedes have two or four pairs per segment, giving them a denser, wave-like leg motion.
- Speed: Centipedes are fast runners. Millipedes move slowly and deliberately.
- Behavior: Centipedes are predators that hunt other bugs. Millipedes feed on decaying plant material and don’t hunt anything.
- Defense: A disturbed centipede sprints away. A disturbed millipede curls up.
Despite their names, neither one actually has a hundred or a thousand legs. Most millipede species top out at fewer than a hundred legs, and house centipedes max out at 30.
There’s one more possibility worth mentioning: garden symphylans, which are tiny white creatures (under a quarter inch long) with 12 pairs of legs. These are uncommon indoors and easy to distinguish by their small size and pale color.
Why They’re in Your House
House centipedes come inside for three reasons: moisture, prey, and shelter. They need damp environments to survive because they dry out quickly in low humidity. Basements, bathrooms, laundry rooms, and crawl spaces are their preferred zones. If your home has plumbing leaks, poor ventilation, or chronically humid lower levels, it’s centipede-friendly territory.
The prey factor is worth paying attention to. House centipedes eat silverfish, cockroaches, carpet beetle larvae, spiders, bed bugs, and crickets. If you’re seeing centipedes regularly, they’re likely feeding on other pests you haven’t noticed yet. In that sense, they’re actually doing you a favor, though most people understandably don’t want that favor performed on their bathroom wall at 2 a.m.
Cold weather also drives them indoors. During winter, heated homes offer warmth they can’t find outside, and severely dry outdoor conditions in summer can push them in as well.
Are They Dangerous?
House centipedes can technically bite, but they rarely do, and their jaws often can’t break human skin. Even when a bite does occur, it’s comparable to a mild bee sting and resolves on its own. They carry no diseases, don’t infest food, and don’t damage wood, fabric, or furniture. They’re one of the least harmful creatures you can find in a home.
How to Reduce Their Numbers
You don’t need pesticides to deal with house centipedes. The single most effective step is lowering your indoor humidity. A dehumidifier that keeps levels between 30% and 50% makes your home inhospitable to them. Below 40% humidity, centipedes dry out fast and can’t survive long. Run bathroom exhaust fans for at least 20 minutes after showers, and make sure those fans vent outside rather than into your attic. Fix any plumbing leaks, and wrap cold-water pipes that collect condensation in humid weather.
Sealing entry points keeps new ones from coming in. Check around basement windows, pipe penetrations, and door thresholds. The spot where your home’s framing meets the foundation (the rim joist and sill plate junction) is a commonly overlooked entry point. Use exterior caulk for cracks under a quarter inch and low-expansion foam for larger gaps. Brush-type door sweeps and 20-mesh screens on foundation vents close off the remaining routes.
Outdoor Changes That Help
What’s happening right outside your walls matters just as much as what’s inside. Create a three-foot plant-free zone around your foundation. Replace wood mulch with gravel or stone, which stays drier and offers fewer hiding spots for centipedes and their prey. Keep shrub canopies pruned at least 12 inches away from exterior walls. Remove leaf litter, grass clippings, and decorative timbers from the foundation perimeter.
Grade the soil so it slopes away from your house for at least 10 feet, and extend downspouts well away from the foundation. Clean gutters regularly. All of this reduces the moisture that accumulates near your home’s base, which is exactly where centipedes gather before finding their way inside.
Dealing With Ones Already Inside
A vacuum is the simplest tool for individual centipedes. Sticky traps placed along baseboards serve double duty: they catch centipedes and reveal which rooms have the most activity, helping you target your moisture-reduction efforts. Diatomaceous earth, a fine powder made from fossilized algae, can be applied in thin layers inside wall voids, around sill plates, and in pipe chases. It works by physically drying out any centipede that crawls through it.
Reducing clutter on basement and garage floors also helps. Centipedes hide in cardboard boxes, piles of stored items, and anything sitting directly on concrete. Elevating storage off the floor and switching to sealed plastic bins removes their preferred daytime hiding spots. If you eliminate the moisture and the prey, the centipedes will move on to somewhere more hospitable.