House Centipedes & Millipedes: What They Actually Are
House centipedes are one of the most disliked household arthropods despite being one of the most useful. They eat cockroaches, silverfish, bed bugs, ants, spiders, and other things you actually don't want in your home. They rarely bite humans, and when they do the result is comparable to a bee sting and only happens if you handle one.
Millipedes are even more harmless. They eat decaying plant matter and don't bite at all. The defensive secretion some species release smells unpleasant and can stain skin briefly, but they don't damage homes or threaten people.
Both species are moisture-driven. Treat the moisture and they disappear on their own.
Telling them apart
| Centipede | Millipede | |
|---|---|---|
| Legs per segment | One pair | Two pairs |
| Body | Flatter, faster | Round, slow |
| Movement | Quick, darting | Slow, wave-like |
| Defensive behavior | Bites (very rarely on humans) | Curls into spiral; chemical secretion |
| Diet | Predator — other insects | Scavenger — decaying plant matter |
| Typical indoor sighting | Bathroom, basement | Mass migration into basements after rain |
House centipedes (Scutigera coleoptrata)
The species most commonly found indoors. 25–40mm long with 15 pairs of long, thin legs that make them look much larger. Bands of dark color across the back. Capable of striking speed — they can disappear under a baseboard before you've finished reaching for a shoe. They prefer damp environments: basements, bathrooms, under sinks.
They eat other arthropods. A house with house centipedes typically has, or recently had, a meaningful population of cockroaches, silverfish, ants, or similar. Eliminate the prey and the centipedes leave.
Should you kill them?
Most entomologists and IPM specialists actively recommend leaving house centipedes alone. They are nocturnal, generally unseen, and provide free biological pest control. If you find one in a kitchen or bedroom, capture in a cup and release outside. If you'd rather not, a shoe works fine — they reproduce slowly and an individual house has at most a few dozen.
Millipedes
Common species in U.S. homes include the greenhouse millipede and various native species. Body is segmented, cylindrical, and dark brown to black. Most are 25–40mm long; some species reach 75mm or larger.
Indoor presence is usually transient. After heavy rains in spring or fall, large numbers may migrate from saturated soil into basements and walk-out lower levels. They typically die within a few days indoors because conditions are too dry. Sweep them up and discard.
If you live near woods or have heavy organic mulch beds adjacent to the foundation, periodic millipede migrations are nearly impossible to fully prevent.
The shared fix — reduce moisture
Both centipedes and millipedes need humidity above ~60%. Drop the humidity and they cannot establish indoor populations.
- Run dehumidifiers in basements and crawlspaces. Aim for 45–55% RH.
- Install vapor barriers on crawlspace soil floors — 6-mil polyethylene with seams taped and edges turned up.
- Improve drainage outside — extend downspouts, fix grading that slopes toward the house, add French drains in chronically wet areas.
- Repair plumbing leaks — even slow drips under sinks and behind toilets sustain enough humidity for centipede populations.
- Move mulch back from the foundation — at least 12 inches of bare ground or gravel.
- Clean up leaf litter within 5 feet of the building.
The indirect fix — reduce prey
Specifically for house centipedes: addressing their food source (other insects) cuts the population. If you have an underlying silverfish, cockroach, or ant problem, treating that resolves the centipede issue as a side effect.
Exclusion
- Door sweeps on basement exterior doors.
- Seal cracks in foundation, especially around utility penetrations.
- Cover floor drains with appropriate traps or screens.
- Check window wells in basements — clear of debris and install a window well cover if migrations are seasonal.
Pesticide use
Rarely necessary or effective. A perimeter pyrethroid treatment around the foundation in spring (before millipede migration season) reduces outdoor populations entering — but moisture reduction does the same job permanently. Indoor sprays kill the visible individuals but don't change the underlying conditions.
When to call a professional
- Recurring large millipede migrations despite drainage and moisture interventions.
- Persistent house centipede presence indicating a hidden prey source you can't find (often German cockroaches or silverfish in wall voids).
- Severe basement moisture issues requiring engineered solutions (sump pumps, interior drain tile, foundation sealing).
Frequently asked questions
Can house centipedes hurt me?
Theoretically — they have venom they use to subdue prey. Bites on humans are rare and usually only happen if you grab one. The bite is comparable to a bee sting in pain; medically significant reactions are very uncommon.
What about giant tropical centipedes?
The redheaded centipede (Scolopendra heros) and similar tropical species in the southwestern U.S. can deliver more painful bites and are large (150mm+). They're outdoor species and rarely enter homes. Use gloves when handling firewood and yard debris in their range.
Are millipedes poisonous?
The defensive secretion some species release contains compounds that can irritate eyes and skin briefly, and a few tropical species produce more potent secretions. U.S. species rarely cause problems. Wash hands after handling and avoid touching your eyes.