The centipede you’re most likely seeing in a Pennsylvania home is the house centipede, a fast-moving, long-legged predator that’s been established in the state since 1849. Originally from the Mediterranean, house centipedes can’t survive Pennsylvania winters outdoors but thrive year-round inside heated buildings. While they look alarming, they’re harmless to people and actually eat many of the pests you’d rather not have in your home.
Outside, Pennsylvania’s forests, gardens, and leaf litter also host stone centipedes and soil centipedes, smaller species that rarely make it indoors and quickly die if they do. The house centipede is the one you’ll encounter in basements, bathrooms, and kitchens, so it’s worth understanding what it is and what draws it inside.
How to Identify a House Centipede
House centipedes are about one inch long (not counting their legs), but their 15 pairs of extremely long, banded legs make them look much larger. Including the leg spread, a full-grown adult can appear two to three inches across. Their bodies are yellowish-gray with three dark stripes running lengthwise, and the legs have alternating light and dark bands that give them a striped appearance.
Two features make house centipedes instantly recognizable. First, their legs get progressively longer toward the back of the body. The final pair is so long and thin that it mimics the antennae at the front, making it hard to tell which end is which at a glance. Second, they’re fast. House centipedes can sprint across walls and ceilings at surprising speed, which is often how people first notice them.
Their long antennae, which can contain hundreds of tiny segments, help them detect prey in the dark. The first pair of legs is actually modified into venom-delivering claws used to paralyze small insects, not for walking.
Centipedes vs. Millipedes
Both show up in Pennsylvania basements, but they’re easy to tell apart once you know what to look for. Centipedes have one pair of legs per body segment, and those legs stick out visibly from a flat body. Millipedes have two pairs of legs per segment, tucked under a rounded, tube-shaped body. Centipedes are fast predators with long antennae. Millipedes are slow-moving scavengers that feed on decaying plant material and move in a wave-like motion.
Centipedes always have an odd number of leg pairs, ranging from 15 to 177 depending on the species. Millipedes typically have between 40 and 400 pairs. If the creature you found curls into a tight spiral when disturbed, it’s a millipede. If it darts away at high speed, it’s a centipede.
Are They Dangerous?
House centipedes can technically sting using their modified front legs, but they almost never do. Their venom claws are designed for subduing small insects and are often too weak to break human skin. In the rare cases where a sting does occur, the result is mild, localized pain and redness similar to a bee sting, resolving on its own. Washing the area with soap and water and applying a wrapped ice pack for 15 minutes is sufficient.
The only real concern is an allergic reaction, which is uncommon but possible with any venom. Signs like hives, swelling around the mouth or throat, dizziness, or trouble breathing after a sting would require immediate medical attention. For the vast majority of people, a house centipede encounter is startling but completely harmless.
What Draws Centipedes Into Pennsylvania Homes
Moisture is the primary factor. Centipedes and millipedes are extremely sensitive to water loss, and they seek out damp environments to survive. In Pennsylvania, basements, crawl spaces, and bathrooms provide the humidity they need, especially during the colder months when outdoor conditions become lethal for them. House centipedes are unique among centipede species in that they can tolerate the drier air found in other rooms of a home, which is why you might spot one in a hallway or bedroom.
Conditions around the outside of your home matter just as much. Thick mulch beds, leaf litter, woodpiles, and dense plants against the foundation create moist microclimates that attract centipedes and, critically, the insects they eat. If there’s a moisture-rich corridor leading from your yard to a gap in your foundation, centipedes will follow it inside.
What They Eat
House centipedes are generalist predators that hunt at night. They feed on spiders, cockroaches, silverfish, carpet beetle larvae, ants, and other small arthropods. They use their long antennae and rear “sensing” legs to locate prey, then lasso insects with specialized whip-like tips on their legs before delivering venom with their front claws.
This diet is why many pest professionals consider house centipedes a sign rather than a problem. A few centipedes in a basement are normal. A large number of them suggests a robust population of prey insects living in your walls or crawl spaces, which is the real issue worth addressing.
How to Keep Centipedes Out
Reducing moisture is the single most effective step. Fix plumbing leaks, wrap cold-water pipes that sweat in humid weather, and run bathroom exhaust fans for at least 20 minutes after showers (vented outside, not into the attic). In basements and crawl spaces, use a dehumidifier to keep indoor humidity between 30 and 50 percent. Centipedes dry out and die quickly when humidity drops below 40 percent.
Outside, grade the soil so it slopes away from your foundation for at least 10 feet. Keep gutters clean and extend downspouts well away from the house. Replace wood mulch near the foundation with gravel or stone, which stays drier and offers fewer hiding spots. Create a plant-free zone of about three feet around the perimeter, and prune shrub canopies at least 12 inches from exterior walls. Remove leaf litter, decorative timbers, and anything else that holds moisture against the foundation.
Sealing Entry Points
Check around basement windows, pipe penetrations, door thresholds, and where the rim joist meets the sill plate, a commonly overlooked gap. Seal cracks under a quarter inch with exterior caulk and fill larger gaps with low-expansion foam. Install brush-type door sweeps on exterior doors and make sure foundation vents have fine mesh screens (20-mesh or smaller).
Trapping and Treatment Options
Vacuuming centipedes when you see them is the simplest direct approach. Sticky traps placed along baseboards help identify where centipedes are most active and catch them passively. Diatomaceous earth or silica gel dust applied in thin films around sill plates, wall voids, and pipe chases works by drying out centipedes that cross treated areas. Boric acid dust in wall voids and entry points provides longer-lasting control with low risk to people and pets. For persistent problems, residual insecticide sprays can be applied around the home’s exterior, focused on known activity areas rather than broad coverage.
The most lasting fix is always the indirect one: eliminate the moisture and seal the gaps. Without damp conditions and a food supply of smaller insects, centipedes have no reason to stay.