Centipedes vs. Millipedes: What’s the Difference?

Something with far too many legs just shot across the basement floor and disappeared behind the water heater. We hear a version of this story every week, usually paired with a blurry phone photo taken a half second too late. Nine times out of ten, the culprit is either a centipede or a millipede, and telling the two apart is easier than most people expect.

Centipedes have one pair of legs per body segment, splayed out to the sides of a flattened body, and they hunt insects with venom. Millipedes have two pairs per segment tucked under a rounded body, move slowly, and eat decaying plants. One sprints when threatened. The other coils up.

That’s the short version. The longer version is worth a few minutes, because these two behave nothing alike once they get indoors, and which one you have changes what should be done about it.

Key Differences at a Glance

Plenty of detail follows, but if you only remember six things, make it these:

• Legs per segment: Centipedes have one pair. Millipedes have two.
• Leg position: Centipede legs splay out from the sides. Millipede legs sit directly under the body.
• Speed: Centipedes sprint. Millipedes plod along and burrow.
• Diet: Centipedes hunt and kill insects with venom. Millipedes eat rotting leaves and wood.
• Defense: Centipedes run or pinch. Millipedes coil into a spiral and release a foul-smelling fluid.
• Body: Centipedes look flat from the side, with long antennae. Millipedes look round, with short antennae.

Here’s the full picture side by side:

Legs Tell the Real Story

Leg count gets all the attention, but leg arrangement is the difference that never lies. Look at any single body segment. A centipede has exactly one pair of legs attached there, and those legs angle out to the sides like oars. A millipede has two pairs on most segments, planted directly beneath the body.

Scientists named the groups for this. Millipedes belong to the class Diplopoda, which means double feet. Centipedes are Chilopoda. Both sit inside a larger group called myriapods, a name that roughly translates to countless feet, which feels about right when one is crossing your laundry room floor.

That arrangement also explains how each one moves. Side-mounted legs give centipedes a sprawling, whip-fast running style, with long rear legs trailing behind. Leg pairs stacked under the body turn millipedes into tiny bulldozers, rippling forward in slow waves with enough traction to push through packed soil and leaf litter.

How Many Legs Do They Actually Have?

Neither name is honest. Centi means one hundred, milli means one thousand, and both numbers miss the mark.

Centipedes carry anywhere from 15 to 191 pairs of legs depending on the species, and the pair count is always odd. That quirk means no centipede on Earth has exactly 100 legs. Most species you’d meet around the Midwest land between 30 and 50 legs total.

Millipedes usually run between 40 and 400 legs. For more than a century, the record holder topped out around 750, so the name looked like pure exaggeration. Then in 2021, researchers in Western Australia pulled a pale, threadlike millipede called Eumillipes persephone from soil about 200 feet underground and counted 1,306 legs. One millipede finally earned the title.

Body Shape, Speed, and Other Quick Tells

Can’t get close enough to count legs? Shape and behavior give it away from across the room.

Viewed from the side, a centipede looks flattened, almost ironed, with long antennae out front and rear legs so long they’re sometimes mistaken for a second set of antennae. A millipede looks like a moving cable, round and smooth, with stubby antennae you can barely see.

Color helps too. The house centipede, the species we find indoors most often, is yellowish gray with three dark stripes down its back and banding on the legs. Most millipedes in our region are dark brown to black, sometimes with a reddish tint.

Behavior settles any remaining doubt. Flip on a light and a centipede bolts for cover at a speed that seems unfair for something that small. A millipede freezes or winds itself into a tight coil. If it outruns your shoe, it was a centipede. If it curls up like a tiny cinnamon roll, millipede.

Which One Is Dangerous?

Neither, in any serious sense. They don’t spread disease, damage your home, or contaminate food. Centipedes are the only one of the pair that can actually bite, though, and millipedes counter with a chemical trick of their own. The distinction people usually reach for is venomous versus poisonous: centipedes inject venom, while millipedes secrete substances that bother whatever touches them.

Do Centipedes Bite?

Yes, though pinch is the better word. A centipede’s front pair of legs evolved into forcipules, curved pincers plumbed with venom glands. They use them to paralyze prey, and on rare occasions they’ll use them on a person who grabs one, steps on one barefoot, or traps one against skin.

For most people, the result feels like a bee sting. Sharp pain at first, then redness and some swelling that fades within hours and rarely lingers past a day or two. Wash the spot with soap and water and hold a cold compress on it. Anyone with insect venom allergies, along with young kids, deserves a closer watch, and a strong reaction is worth a call to a doctor.

For what it’s worth, the house centipedes we see in basements are reluctant biters and often can’t even break skin.

Can a Millipede Hurt You?

A millipede cannot bite or sting. Nothing on its body is built for it. What it can do is release a foul-smelling fluid from glands along its sides when handled. Depending on the species, that fluid can irritate skin, leave a temporary brownish stain, or burn if it gets rubbed into the eyes. A few species even produce trace amounts of hydrogen cyanide, which sounds alarming and amounts to a bad smell and mild irritation at the doses involved.

Wash your hands after touching one and keep them away from your face. Dogs that mouth millipedes sometimes drool or paw at their muzzle for a few minutes from the taste, and it usually passes on its own.

So if the question is which one is worse, a centipede can hurt you slightly, and a millipede can mostly just offend you.

What They Eat

Centipedes are hunters. They run down silverfish, spiders, cockroach nymphs, moths, ants, and nearly any other small arthropod they can catch, killing with a venomous pinch. Millipedes work the other end of the food chain. They’re recyclers, feeding on dead leaves, rotting wood, and other decaying plant matter, and garden soil is better for the work they do.

Diet is the part of this comparison with real stakes for homeowners. A predator doesn’t hang around where there’s nothing to hunt. When we find house centipedes established in a home, there’s nearly always a food supply keeping them there, often silverfish or spiders the homeowner hasn’t noticed yet. Millipedes face the opposite problem indoors: your house has nothing on the menu for them at all.

Should You Kill House Centipedes?

Honest answer from people who remove pests for a living: the house centipede is more ally than enemy. One of them eats a steady stream of roaches, silverfish, moths, and spiders. It builds no nest, damages nothing, and almost never bites. Squash it if it startles you. We understand completely.

But if you’re seeing them regularly, picking them off one at a time misses the point. The smarter move is to deal with the prey insects drawing them in. Take away the food and the hunters leave on their own.

Where They Live and Why They Wander Inside

Outdoors, both spend their days under the same cover: rocks, logs, leaf litter, mulch beds, and the damp soil along foundations. Both come out at night, both have weak eyesight, and both follow moisture. Millipedes depend on it completely. Centipedes prefer it but tolerate drier ground.

Indoors, that pulls them toward the same rooms we get called about: basements, crawl spaces, bathrooms, laundry rooms, sump pits, and floor drains. Window wells collect both, and we sweep plenty out of garages every spring and fall.

Why Am I Suddenly Seeing Millipedes in My House?

Blame the weather. After several days of heavy rain, the soil becomes too saturated for millipedes to breathe, and entire populations climb out at once. They scale foundations, slip under door thresholds, and show up on basement floors by the dozens, sometimes the hundreds. Long dry spells trigger the same march in reverse, with millipedes wandering in search of moisture, and cooling fall temperatures send another wave toward warm foundations.

There’s good news buried in that mess: they aren’t breeding in your house, and they aren’t trying to stay. They wandered in, and most won’t survive the trip.

Which One Can Survive Indoors?

Only one of these can make a real life inside, and it’s the centipede. The house centipede (Scutigera coleoptrata) arrived in North America from the Mediterranean generations ago and is the one species fully adapted to indoor living. It can spend all of its six or seven years inside, breeding in damp basements and hunting year round.

Millipedes can’t pull that off. A home’s air is too dry for them, and most die within a few days of getting inside, which is why so many turn up already curled and crisp along baseboards. That pattern tells us something during inspections. A steady trickle of centipedes points to an established indoor food source. Piles of millipedes point to entry gaps and a moisture problem at the perimeter.

Bugs That Get Mistaken for Both

A few regulars get misidentified on service calls all the time:

• Silverfish. Insects, not myriapods. Six legs, a teardrop-shaped silvery body, and three bristles off the tail. People mix them up with house centipedes constantly, partly because centipedes eat them.
• Sowbugs and pillbugs. Land crustaceans with seven pairs of legs. Pillbugs roll into a tight ball when disturbed, which gets them confused with coiled millipedes. A pillbug forms a sphere, like a tiny armadillo. A millipede winds into a flat spiral.
• Garden symphylans. Tiny, white, fast soil dwellers with 12 pairs of legs that look like newborn centipedes. They stay in garden beds and greenhouse soil, where they nibble plant roots.

Quick field rule: a long segmented body with legs running its whole length means centipede or millipede. Anything else is a different pest with a different playbook.

How to Keep Both Out of Your House

Two levers control both pests: dry it out and seal it up. Nearly everything on this list pushes one of those levers.

• Run a dehumidifier in the basement or crawl space, fix dripping pipes and faucets, and use exhaust fans in bathrooms and laundry rooms.
• Keep gutters and downspouts moving water away from the house, and let soil along the foundation dry out between waterings.
• Rake mulch and leaf litter at least six inches back from the foundation, and store firewood off the ground and away from exterior walls.
• Install door sweeps on exterior doors, caulk foundation cracks, seal gaps around pipe and utility penetrations, and clean out window wells.
• For centipedes specifically, knock down their food supply. Treating the silverfish, spiders, and roaches in a home does more to evict centipedes than chasing the centipedes themselves.

A treated barrier around the foundation closes the loop, especially ahead of the soggy spring stretches and fall cooldowns that push these pests indoors across the Midwest. That timing is exactly what our recurring service is built around, and millipede invasions and basement centipedes are two of the most common reasons customers call us in the first place.

So the next time something multi-legged crosses your floor, check two things before it disappears: how the legs sit and what it does when cornered. Sprinter with side-mounted legs, centipede. Slow coil, millipede. And if the photo comes out blurry anyway, send it our way. We’ve identified pests from far worse.

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