House Centipedes in Your Basement: What They're Really Telling You

Quick answer

House centipedes are predators. They don’t eat your food, your wood or your fabric — they eat other insects. So a house centipede in your basement is not really a centipede problem: it’s a signal that there is enough prey down there to feed one, and usually enough moisture to keep both alive. Killing the centipede you see changes nothing, because the food supply that attracted it is still there. The fix is to remove the prey population and dry the space. Sani IQ inspections are $95, credited when you book the treatment. General Insect Control starts at $395 exterior / $475 interior and exterior; the year-round Essentials plan is $1,195.

You go down to move the laundry, flick the light on, and something with an alarming number of legs sprints across the concrete at a speed no insect that size should be capable of and disappears under the utility sink.

That’s Scutigera coleoptrata, the house centipede, and the reaction it produces is out of all proportion to the harm it does. Here’s what’s actually going on — and why the centipede is the least interesting part of the story.

The counterintuitive part: they’re the good news and the bad news at once

Almost every household pest tells you something about your house. Ants tell you about a food source. Cluster flies tell you about a south-facing wall. Mice tell you about a 6 mm gap.

House centipedes tell you something more useful: there is a standing insect population in your basement large enough to sustain a predator.

They eat spiders, silverfish, firebrats, carpet beetle larvae, cockroaches, ants, and the small soft-bodied insects that live in damp voids and floor drains. They hunt at night, alone, and they eat a great deal for their size. A centipede does not move into a basement that has nothing in it.

That’s why the standard response — squash it, spray the baseboard, move on — accomplishes nothing. You’ve removed one predator from a habitat still producing prey. The next centipede is already on its way, and the silverfish population you didn’t know you had just lost a check on its numbers.

The second signal: moisture

The other thing house centipedes need is humidity. They have no waxy cuticle layer to seal in water the way beetles do, so they dry out quickly and stay where it’s damp — which in an Ontario home means the basement, the crawlspace, the space behind a laundry tub, under a deck, and inside a floor drain.

If you’re seeing them regularly, walk the basement with two questions:

• Where is water getting in or sitting? Foundation seepage after rain, a slow supply-line drip, a dehumidifier that stopped working, condensation on cold-water lines, a laundry standpipe, a sump that never fully dries, a floor drain trap that has gone dry and is venting sewer humidity.
• Where is organic material staying damp? Cardboard boxes on a concrete floor are the classic one. Cardboard absorbs floor moisture, the starch in the corrugation feeds silverfish, and silverfish feed centipedes. A basement stacked with cardboard is a food-production facility with a predator on staff.

Relative humidity below about 50% makes a basement genuinely inhospitable to house centipedes and to most of what they eat. That single change does more than any spray.

Why late summer and fall is when you see them

Two things converge at the end of August. The outdoor population is at its seasonal peak — centipedes that spent the summer under mulch, patio stones, deck boards and leaf litter are at maximum numbers. And as nights cool, the stable warm humidity of a heated basement becomes the best habitat available. They come in through the same openings everything else uses: window wells and basement window frames, the sill plate gap, floor drains, utility penetrations, and the door from an attached garage.

You’ll often see a cluster of sightings over two or three weeks in September, then very little through winter. That’s not the problem resolving — it’s the population settling in behind the drywall, where it stays fed all winter.

Are they dangerous?

Practically, no. House centipedes have modified front legs that deliver venom to prey, but the structure is too weak to reliably break human skin, and most people who share a basement with them for years are never bitten. When it happens it’s comparable to a bee sting. They don’t carry disease, damage structures, contaminate food, or chew anything.

They are a legitimate quality-of-life problem, though. A finished basement you avoid using is a room you’re paying for and not getting. And the insect population they point at isn’t always harmless — carpet beetle larvae damage textiles, silverfish damage paper, and a large prey base usually means moisture doing its own slow damage.

Why spraying centipedes never works

Three reasons, worth knowing before you spend money on a can. You can’t treat what you can’t reach — centipedes live in wall voids, under slabs, in floor drains and inside block cores, so the one on the floor is a fraction of what’s present. They’re the consequence of a population, not the population — killing predators while leaving the prey base intact produces a dip and a fast recovery. And residual baseboard sprays target the wrong surfaces, since centipedes move fast on open floor and rest in voids.

What reduces them is treating the whole ecosystem: the void-dwelling insects they eat, the exterior harbourage they come from, the entry points, and the humidity supporting all of it.

What actually fixes it

Dry it out.

• Run a dehumidifier to hold the basement below 50% RH, and check that it’s actually reaching that — most people set one and never verify.
• Fix the seepage, the drip, the dry floor-drain trap (pour a litre of water down unused drains monthly).
• Insulate sweating cold-water lines.
• Get cardboard off the floor and, ideally, out of the basement — sealed plastic bins instead.

Reduce harbourage, inside and out.

• Move firewood, leaf litter, mulch beds and stacked patio stone away from the foundation. That’s where the outdoor population lives.
• Clear the window wells. Wet leaf litter in a window well is a centipede colony pressed against a gap in your window frame.
• Declutter the floor perimeter inside — anything sitting directly on concrete is a harbourage.

Close the entries.

• Seal the sill plate seam, the utility penetrations, and gaps around basement window frames.
• Screen floor drains and window wells.
• Fix the door sweep between an attached garage and the house.

Deal with the prey population.

This is the step homeowners can’t do themselves, and it’s the one that actually ends the cycle. A general insect treatment targeting the void-dwelling insects — silverfish, carpet beetles, spiders, ants and the rest — removes the food supply. Do that alongside the moisture work and the centipedes leave on their own, because there’s nothing left to hunt.

What it costs

Canonical Ontario pricing as of 2026:

Service	Price
Professional inspection	$95, credited when you book the treatment
General Insect Control	from $395 exterior / $475 interior + exterior
Essentials plan (year-round)	$1,195
VIP plan	from $1,395

One-time services carry a 60-day guarantee.

Here’s the honest recommendation, and it’s not the cheapest line on that table.

A one-time general insect treatment is the right way to start — it knocks down the current prey population and it’s guaranteed for 60 days. But look at what actually drives a basement centipede problem: an outdoor population that peaks every August, seasonal moisture that returns every spring thaw and every wet autumn, and a prey base of silverfish and carpet beetles that rebuilds from eggs already in the voids. None of those are one-time conditions. They’re annual ones.

The year-round Essentials plan at $1,195 is what actually keeps the cycle broken — scheduled seasonal treatments timed to the exterior population, interior void work, monitoring between visits, and return visits when something changes rather than a new invoice each time. A basement you’ve treated once in September is a basement that’s likely to need treating again next September, and the one after that.

If you want to know which plan fits your house before talking to anyone, the free quote quiz takes about a minute. If you’d rather see the tiers side by side, they’re all on the plans and pricing page.

We handle basement and general insect work across the GTA and beyond — including Toronto, where the older housing stock’s block foundations and stone basements are exactly the habitat this article describes; Etobicoke, where mature tree cover and 1950s–60s basements produce the same pattern; and Vaughan and the York Region suburbs. There’s more on the species we deal with in the pest library.

Call (705) 302-1887 to book an inspection.

Frequently asked questions

Should I kill house centipedes or leave them alone? Ecologically, leaving them alone is defensible — they’re eating things you’d like gone. Practically, most people don’t want them in a finished basement, and either way the centipede isn’t the issue. Fix the moisture and the prey population and the question resolves itself.

Do house centipedes bite people? Very rarely. Their venom apparatus is adapted for small insects and usually can’t penetrate human skin. When a bite does occur it’s roughly comparable to a bee sting and resolves without treatment.

I only see one or two. Is that an infestation? House centipedes are solitary hunters, so you’ll rarely see many at once even when a fair number are present — they don’t cluster the way ants or cluster flies do. Repeated sightings over weeks means an established population, not a wanderer.

Does a centipede in my basement mean I have silverfish? Not necessarily silverfish specifically, but it means something is down there in numbers. Silverfish, carpet beetle larvae, spiders, ants, small flies and firebrats are the usual candidates. An inspection identifies which.

Will a dehumidifier alone get rid of them? It’s the single most effective thing you can do yourself, and in a mild case it may be enough. In an established case it reduces the population without eliminating it, because the prey base and the exterior source remain.

Do they get into the rest of the house? Sometimes — bathrooms and ground-floor utility areas are the usual next stop, since they’re the next most humid spaces. Sightings upstairs generally mean the basement population has grown past what the basement supports.

Is the $95 inspection an extra charge? No. It’s credited in full when you book the treatment. It only stands as a charge if you decide not to proceed, and it covers the technician’s time on site.

Sani IQ is BBB Accredited with a 5.0 rating across 126 Google reviews, carries $5M liability coverage, is licensed under the Ontario Pesticides Act and registered with MECP. Our technicians are employed, licensed and background-checked. We use reduced-risk products and methods wherever they’ll do the job.