The bug you spotted with lots of legs is most likely a centipede, millipede, or one of a few other common arthropods that show up in homes. The number of legs is actually the fastest way to figure out exactly what you’re dealing with, since each type has a distinct count and body shape.
House Centipedes: The Fast Ones
If the bug was fast, yellowish, and had long, spindly legs fanning out from its body, you almost certainly saw a house centipede. These are the most common “lots of legs” bugs found indoors, and they startle people more than almost any other household pest. Adults have 15 pairs of legs (30 total), with the rear legs on females stretching to nearly twice the length of the body itself. The body is about one to one and a half inches long, dirty yellow with three dark stripes running lengthwise, and the legs are banded light and dark.
House centipedes are harmless to people. They’re actually predators that eat silverfish, carpet beetle larvae, cockroaches, and spiders. Seeing a lot of them can signal a bigger pest population in your home, since they go where the food is. They prefer damp, dark areas like basements, bathrooms, and crawl spaces.
Millipedes: The Slow, Curling Ones
If the bug was dark brown, moved slowly in a wave-like motion, and curled into a ball when you touched it, that’s a millipede. Millipedes have a rounded, cylindrical body compared to the flat body of a centipede, and they carry two pairs of tiny legs per body segment rather than one. Most species you’d find around the house have somewhere between 30 and 90 legs, though larger outdoor species can have several hundred.
The name “millipede” means thousand legs, and one species actually lives up to it. A millipede discovered more than 60 meters underground in Australia, called Eumillipes persephone, holds the record at 1,306 legs on females and 818 on males. You won’t find that one in your bathroom, though. The millipedes that wander indoors are garden dwellers that got lost. They need moisture to survive and typically die quickly in the dry conditions inside a home. They feed on decaying plant material, not your food or furniture.
Pillbugs and Sowbugs: The Roly-Polies
These gray, oval-shaped creatures have 14 legs (seven pairs) and are about a third to three-quarters of an inch long. Pillbugs are the ones that roll into a tight ball when disturbed. Sowbugs look similar but can’t roll up and have two small tail-like appendages at the rear.
Here’s something most people don’t know: pillbugs and sowbugs aren’t insects at all. They’re crustaceans, more closely related to shrimp and crabs than to any bug. They breathe through gill-like structures and need constant moisture, which is why you find them under flower pots, mulch, and damp basement corners. They eat decaying leaves and plant matter and pose no threat to people.
Silverfish: Fewer Legs Than You Think
Silverfish often end up on the “lots of legs” list because of how they look when they move. They’re silver-gray, teardrop-shaped, and dart across surfaces so quickly that their body parts blur together. In reality, they only have six legs, the same as any insect. What creates the many-legged illusion is three long bristle-like appendages trailing from their rear end, plus two antennae up front. At a glance, those extras look like additional legs.
Silverfish are attracted to starchy materials like paper, book bindings, wallpaper paste, and cardboard. They love humidity and are most active at night, which is why you might spot one when you flip on the bathroom light at 2 a.m.
How to Tell Them Apart Quickly
- Flat body, long legs, moves fast: house centipede (30 legs)
- Round body, tiny legs, moves slowly, curls up: millipede (60+ legs)
- Gray, oval, armor-like plates: pillbug or sowbug (14 legs)
- Silver, teardrop-shaped, bristly tail: silverfish (6 legs)
Are Any of Them Dangerous?
None of the common many-legged household bugs pose a real threat. House centipedes technically have venom that they use to subdue prey, but their jaws rarely penetrate human skin, and even when they do the result is a mild, short-lived sting comparable to a bee sting. The vast majority of centipede encounters resolve within hours to a few days with no lasting effects. Millipedes, pillbugs, and silverfish don’t bite at all.
The centipede species that can deliver a genuinely painful bite belong to the Scolopendra group, tropical giants that grow 3 to 8 inches long. If you live in the southern United States or a tropical region and encounter a large, thick-bodied centipede outdoors, give it space. Even those bites, while painful, are rarely medically serious.
Keeping Them Out of Your Home
Every one of these creatures shares the same basic need: moisture. Reducing humidity inside your home is the single most effective step. Run a dehumidifier in basements and crawl spaces. Make sure water drains away from your foundation rather than pooling near it. Fix leaking pipes, and check that air conditioner condensation lines are draining properly. Installing a plastic vapor barrier over exposed soil in a crawl space helps significantly.
Seal their entry points next. Caulk cracks in your foundation and walls. Fill gaps around drainpipes and vents with steel wool, then seal over it with caulk or expanding foam. Add weather stripping or door sweeps to exterior doors, and caulk around window frames.
Outside, keep leaf litter, grass clippings, and mulch away from the base of your home. If you use mulch in garden beds near the house, keep it between 2 and 4 inches deep. Dethatch your lawn if the layer of dead grass above the soil has gotten thick, since millipedes thrive in that dense mat of organic material. Removing their habitat outdoors means fewer of them end up wandering through your door.