Centipedes and Millipedes in Your House: What They Are and What to Do

There's something uniquely unsettling about watching a house centipede sprint across your bathroom wall at midnight. All those legs moving in a wave. The speed. The way it vanishes behind the toilet before you can react. But here's the thing most people don't realize: that centipede is in your house because something else is in your house first.

Two Very Different Animals

People lump centipedes and millipedes together, but they're about as similar as a cat and a cow. Centipedes are predators. Flat body, one pair of legs per body segment, and fast. They hunt spiders, silverfish, roaches, ants, and even small moths. A house centipede (Scutigera coleoptrata) is basically a tiny exterminator living in your basement rent-free.

Millipedes are slow, round-bodied, and have two pairs of legs per segment. They eat decaying plant matter. Leaf litter, rotting wood, decomposing mulch. They're detritivores. They don't bite, don't damage anything in your house, and curl into a tight spiral when disturbed. Some species release a mildly irritating fluid if handled, but that's it.

Neither one is dangerous to you.

Why They're Inside

Both need moisture. That's the single biggest factor. If your basement, crawl space, or bathroom stays damp, you're rolling out a welcome mat. Centipedes follow their prey indoors. If you have silverfish or roaches living in your walls, centipedes will eventually show up to eat them. Killing the centipedes without addressing the prey population is like shooting the messenger.

Millipedes tend to invade in waves after heavy rain. Soil gets saturated, thousands of them head for higher ground, and your foundation is the nearest dry surface. You'll find them piled against basement walls, in window wells, under door sweeps. It looks alarming but it's temporary. They can't survive indoors long-term because there's nothing to eat.

Identification at a Glance

House centipede: yellowish-gray, 1 to 1.5 inches, extremely long legs that make it look larger, moves fast. Common in basements, bathrooms, and laundry rooms.

Garden centipede: reddish-brown, flat, found under rocks and logs outside. Occasionally wanders in through gaps in the foundation. Bites if handled but it's like a weak bee sting.

Millipede: dark brown or black, round, slow, curls up when touched. Ranges from half an inch to two inches. Shows up in large numbers after rain.

Fixing the Problem

Address the moisture first. Everything else is secondary. Run a dehumidifier in the basement and keep relative humidity below 50%. Fix dripping pipes. Make sure downspouts discharge at least 4 feet from the foundation. Grade soil away from the house so water doesn't pool against the walls.

Outside, pull mulch back 6 to 12 inches from the foundation. Move firewood stacks, leaf piles, and compost bins away from the house. These are millipede breeding grounds. Seal cracks in the foundation with silicone caulk. Check where utility pipes and wires enter the house. Even a quarter-inch gap is enough.

For monitoring, sticky traps (Catchmaster brand, about $8 for a 12-pack) placed along basement walls will tell you how many you're dealing with and where they're traveling. If you're catching more than a handful per week, there's a moisture problem you haven't found yet.

Chemical treatment is rarely needed. If numbers are high, a perimeter application of Demon WP (wettable powder, around $15 per packet) mixed in a pump sprayer and applied to the foundation exterior and 3 feet of soil outward will knock them down. It's a synthetic pyrethroid and lasts about 90 days. Our common pests guide covers similar perimeter treatments for other crawling pests.

A Note About House Centipedes

A lot of entomologists will tell you to leave house centipedes alone. They're not wrong. A single house centipede can eat dozens of pest insects per week. If you see one every few months, it's doing you a favor. If you're seeing them regularly, that's a signal. Your house has a prey population worth hunting. Figure out what they're eating and deal with that. Our pest-proofing guide walks through sealing entry points room by room.

Professional Treatment

Pest control companies charge $100 to $200 for a centipede or millipede treatment. They'll apply a residual barrier around the exterior foundation and treat the interior perimeter of the basement. Honest ones will tell you it's a moisture problem first and a pest problem second.

If millipedes are invading in the hundreds after rain, a one-time exterior treatment is reasonable. For occasional house centipedes, skip the exterminator and buy a dehumidifier instead. You'll spend less money and fix the actual issue.