House Centipedes: The Predator in Your Bathroom
House centipedes eat silverfish, firebrats, carpet beetle larvae, cockroaches and spiders, which makes them one of the few things found indoors that is actively reducing your pest problem. They are venomous in the technical sense, but their forcipules usually cannot pierce human skin and Penn State Extension describes them as harmless. An adult has 15 pairs of legs, 30 in total, and takes about three years to get there. Their presence is a moisture signal.
Almost nobody wants to hear that the fast, many-legged thing in the bath is beneficial. It is still the accurate answer, and it changes what you should do about it. The centipede is a symptom of two things: a damp building and a supply of other insects.
What it is and what it is not
Scutigera coleoptrata is the only centipede in the United States that completes its whole life cycle indoors. The body is 25 to 38 mm, but the long banded legs and whip-like antennae make the animal look three to four inches across, which accounts for most of the reaction it provokes.
It is regularly confused with two harmless neighbours and one thing it eats. A millipede is slow, cylindrical, and curls into a spiral when disturbed. A silverfish is small, flat, tapered and silver, and is prey rather than predator. The house centipede is the fast one with visibly long legs that disappears when a light comes on.
Our guide to the moisture pests as a group covers how the whole set relates to damp, and our woodlice and sowbugs page deals with the other common crawlspace finds.
The legs are a clock
House centipedes hatch with four pairs of legs and add pairs at each moult, running through five, seven, nine, 11 and 13 before reaching the adult 15 pairs. A specimen with visibly fewer legs is a juvenile, and it means they are breeding on the premises rather than wandering in.
Reaching adulthood takes roughly three years, which is unusual for a household arthropod and worth knowing: an adult house centipede in a basement has been living there, undetected, for a long time. It also means their numbers do not surge the way an insect population can.
Are they dangerous?
Effectively no. What look like front legs are forcipules, a modified first pair of legs carrying venom, which the animal uses on prey. Penn State Extension describes house centipedes as harmless to people, and notes the forcipules are usually not strong enough to break human skin. Where a bite does register it is generally compared to a bee sting and is short-lived.
They do not transmit disease, do not damage the structure, do not contaminate food stores and do not bite while people sleep. The case against them is entirely aesthetic.
What their presence actually tells you
Two things, both more useful than the centipede itself.
The building has a moisture problem. House centipedes need damp conditions and are found in basements, crawlspaces, bathrooms and under sinks. Extension sources frame excessive indoor moisture as evidence of a structural or functional fault in the building, so a centipede population is a free diagnostic pointing at a leak, poor drainage, an unvented crawlspace or failed grading.
There is something for them to eat. A predator persists only where prey persists. A steady centipede population implies a steady population of silverfish, firebrats, carpet beetle larvae, small cockroaches or spiders, most of which are better at hiding. In that sense the centipede is the visible symptom of the infestation you have not found.
Carpet beetle larvae are the one worth acting on, because they damage wool, silk and stored fabrics; our carpet beetle guidance covers that. Silverfish damage paper and starched goods.
Should you kill it?
That is a judgement rather than a technical question, and both answers are defensible. What is not defensible is treating a house for centipedes with insecticide while ignoring the damp that brought them, because that removes the indicator and leaves the cause.
- For an individual centipede, a cup and a card puts it outside. Killing one changes nothing about the population.
- Find the water. A moisture meter or a simple check of the usual suspects: condensing pipes, failed seals around tubs and showers, negative grading against the foundation, blocked gutters, an unvented crawlspace.
- Dehumidify the basement or crawlspace. This is the treatment. Reducing relative humidity removes the habitat for centipedes and for everything they eat.
- Deal with the prey population, which is the actual pest problem and the reason they have stayed.
- Close entry points at grade, since some arrive from outdoor leaf litter and mulch.
- Treat chemically only as a supplement. Residual product applied to a damp basement wall without fixing the damp is a repeat visit, not a solution.
For how this fits a wider recurring programme, see our comparison of monthly and quarterly plans.
Where the published facts stop
Two claims circulate that we could not substantiate. There is no reliable species-specific lifespan figure for Scutigera coleoptrata in the extension literature, which tends to give figures for centipedes generally, sometimes up to about six years. And we found no source quantifying how many insects a house centipede eats per day, so any article giving you a precise number has invented it.
Frequently asked questions
Are house centipedes dangerous?
Not meaningfully. They carry venom in modified front legs called forcipules and use it on prey, but those forcipules usually cannot penetrate human skin, and Penn State Extension describes the species as harmless. They transmit no disease, do not damage buildings and do not contaminate food.
Should I kill house centipedes?
They prey on silverfish, firebrats, carpet beetle larvae, small cockroaches and spiders, so killing them removes a predator of pests you would otherwise pay to control. The more useful response is to treat their presence as a signal: reduce the moisture that supports them and deal with the prey population that is keeping them there.
Why do I have house centipedes?
Damp and food. They require humid conditions and are found in basements, crawlspaces and bathrooms, so a population indicates a moisture fault such as a leak, poor drainage or an unvented crawlspace. Their continued presence also indicates a supply of prey insects living in the same building.
How many legs does a house centipede have?
Thirty as an adult, in 15 pairs. They hatch with four pairs and add more at each moult, passing through five, seven, nine, 11 and 13 pairs. Reaching adulthood takes about three years, so a short-legged specimen indicates they are breeding in the building rather than wandering in.
Sources
- Penn State Extension, house centipede (Scutigera coleoptrata), on leg development, prey and medical significance. extension.psu.edu
- University extension guidance on indoor moisture as an indicator of structural or functional building faults.
