Those dark, worm-like bugs with dozens of tiny legs covering your porch, driveway, or garage floor after a storm are almost certainly millipedes. They’re harmless to people, pets, and your house. They can’t bite, they don’t sting, and they don’t eat wood, wiring, or fabric. They show up in large numbers because heavy rain floods the soil and leaf litter they normally live in, and they crawl toward the nearest dry, solid surface, which is often your foundation. The fix isn’t spraying the ones you see. It’s drying out and sealing the perimeter so the next storm doesn’t send another wave.
San Diego doesn’t get millipede swarms every week, but when the first real rain of the season hits after a long dry stretch, foothill and canyon-adjacent neighborhoods can see hundreds of them on a driveway overnight. Here’s how to tell them apart from look-alikes, why San Diego’s rain pattern triggers it, and what actually stops it.
How to identify millipedes and tell them apart
Millipedes are long, cylindrical, segmented bugs, usually dark brown to black. UC Statewide IPM puts adult millipedes at half an inch to six and a half inches long, depending on the species. The giveaway is the legs: two pairs of legs per body segment on most species, so a millipede appears to have rows of legs rippling down its entire length. When you touch one or it feels threatened, it curls into a tight, flat coil instead of running.
That coiling behavior is the fastest way to separate a millipede from the bug most often confused with it.
| Bug | Legs per segment | Speed | Defense | Bites? |
|---|---|---|---|---|
| Millipede | Two pairs | Slow | Curls into a coil | No |
| House centipede | One pair, long trailing legs | Very fast | Runs and hides | Can pinch, rarely breaks skin |
| Earwig | Six legs total, pincers at rear | Fast, scurries | Pincers, doesn’t coil | No, pincers can pinch |
If it’s fast and darts for cover, it’s a house centipede, which is actually a predator that eats other bugs. If it’s slow and rolls into a spiral when you nudge it, it’s a millipede. Millipedes are decomposers, not predators. They feed on damp, decaying leaves, mulch, and dead plant matter outdoors. They aren’t after your house at all; they end up on it by accident.
Why millipedes invade San Diego homes after rain
Millipedes live in moist soil, mulch beds, leaf litter, and ground cover, usually in numbers nobody notices because they stay hidden under the surface. They need constant moisture to survive, which is exactly why heavy rain causes the sudden swarm. When the ground saturates, water fills the pore spaces in the soil where millipedes live, and they crawl up and out to keep from drowning. Once they’re on the surface, they wander in whatever direction leads them, and a paved driveway, a stucco wall, or a lit porch is often the first solid, open ground they hit.
This is why the pattern is so specific here. San Diego goes months with barely any rain, so leaf litter, mulch, and ground cover build up thick, dry layers where millipede populations grow undisturbed. The first significant storm of the season, usually the first real rain after the summer dry spell, floods all of that at once and pushes every millipede in the yard to the surface simultaneously. Homes backed up to canyons, greenbelts, or heavily landscaped foothill lots see this hardest, since those properties carry the deep leaf litter and mulch beds millipedes need. It’s a well-documented seasonal spike, not a sign anything is wrong with your home. Our San Diego pest season calendar covers when this and other weather-driven pests tend to show up.
Are millipedes dangerous to people or pets?
No, but a couple of things are worth knowing. UC IPM notes that millipedes don’t bite, but some species exude a defensive fluid when handled roughly or crushed that can irritate skin or burn the eyes. It can also leave a brownish stain on skin. Keep it away from your eyes, and wash the area with soap and water if it gets on you.
The one real caution is dogs. Dogs sometimes pick millipedes up in their mouths out of curiosity, and since the defensive fluid is an irritant, it’s worth discouraging that. If your dog mouths one, rinse its mouth with water and call your vet if the irritation doesn’t settle down. Millipedes don’t damage your house, your garden plants, or stored food. Unlike termites or wood-boring beetles, they aren’t structural pests at all.
How to stop a millipede invasion
Millipedes die quickly once they’re inside a house or stranded on dry pavement. Penn State Extension notes they don’t live more than a few days indoors, which is also why treating the inside of the home isn’t necessary. That means the population you see after a storm isn’t building a home inside your walls. The real fix is cutting off the conditions that let so many build up outside in the first place.
- Pull mulch and leaf litter back from the foundation. Keep a several-inch gap of bare soil or gravel between mulch beds and the exterior wall so migrating millipedes hit open, dry ground before they reach the house.
- Fix drainage that pools water against the foundation. Make sure gutters and downspouts direct water away from the house, and grade soil so it slopes away from the foundation rather than toward it.
- Thin out dense ground cover and compost piles near entry points. Millipedes concentrate wherever damp organic matter builds up, so keeping it away from doors and low vents cuts the population close to the house.
- Seal gaps around doors, low vents, and the base of the foundation. Weatherstripping and caulk close the same small openings ants and other ground-level pests use.
- Sweep or vacuum them up rather than spraying indoors. Since they die on their own from the dry indoor environment, a broom and dustpan or a vacuum handles a stray batch on the porch or garage floor faster than any spray would.
A general pest control program that includes a treated perimeter band helps when a property backs up to a canyon or has heavy year-round landscaping, since the same barrier that keeps ants and spiders out also intercepts millipedes migrating toward the foundation.
When to call a pro for millipedes
Most millipede swarms clear up on their own within a few days once the ground dries out, so a single heavy night after a storm usually doesn’t need professional help. It’s worth calling in a pro when the swarms come back every rainy season in the same numbers despite clearing mulch and fixing drainage, or when a heavily landscaped, canyon-adjacent property in places like Poway, Escondido, Ramona, El Cajon, or Alpine keeps sending millipedes toward the house no matter what you change at ground level.
If millipedes keep showing up on your property every time it rains, we can connect you with experienced local pros who handle perimeter and moisture-focused treatment the right way. See our pest control services in Poway page, browse pest control services across San Diego, or call (858) 400-6561 to get matched with someone in your area. When you talk to any company, it’s fair to ask for their license number and verify it at pestboard.ca.gov before they treat.
Frequently asked questions
What are the worm-like bugs with lots of legs in my San Diego yard?
They’re almost certainly millipedes. They’re dark, cylindrical, segmented bugs with two pairs of legs per body segment on most species, and they curl into a tight coil when disturbed instead of running. They live in moist soil, mulch, and leaf litter, and heavy rain pushes large numbers of them to the surface at once.
Do millipedes bite or sting?
No. Millipedes have no biting mouthparts and no stinger. Some species release a defensive fluid when handled or crushed that can irritate skin or burn the eyes, but it isn’t a bite and it isn’t dangerous to people. Wash the area with soap and water if it happens, and keep it away from your eyes.
Why do millipedes show up in my house after it rains?
Millipedes need constant moisture to survive, so when heavy rain saturates the soil they live in, they crawl up and out to keep from drowning. San Diego’s long dry stretch between storms lets millipede populations build up in mulch and leaf litter, so the first big rain of the season floods all of it at once and sends a large wave toward the nearest dry ground, which is often a driveway, porch, or foundation.
Are millipedes harmful to my house, garden, or pets?
Millipedes don’t damage your house, wiring, or stored food, and they don’t harm garden plants since they feed on already-decaying matter. They’re not dangerous to people. The one caution is dogs, since some dogs mouth millipedes out of curiosity and the defensive fluid is an irritant. Rinse your dog’s mouth with water if that happens, and call your vet if the irritation doesn’t settle.
How do I get rid of a millipede invasion?
Pull mulch and leaf litter back from the foundation, fix drainage so water doesn’t pool against the house, thin dense ground cover near entry points, and seal gaps around doors and low vents. Sweep or vacuum any that make it inside rather than spraying, since they die quickly indoors on their own. For a property that floods with millipedes every rainy season, a treated perimeter band from a pro stops most of them before they reach the door.
How is a millipede different from a centipede?
Millipedes have two pairs of legs per body segment on most species and move slowly, curling into a coil when threatened. House centipedes have one pair of long legs per segment, move very fast, and are actual predators that hunt other bugs instead of feeding on decaying plant matter. If it darts across the floor, it’s a centipede. If it curls up and barely moves, it’s a millipede.