Millipedes that show up inside your home are outdoor creatures that wandered in by accident, usually driven by heavy rain or drought. They’re harmless, they don’t bite, and they typically die within a few days indoors because your house is too dry for them. Understanding why they enter and how to seal them out is the most effective way to deal with them.
It’s worth noting upfront: the term “house millipede” is often confused with the house centipede, which is a completely different animal. If the creature you spotted had long, spindly legs and moved fast, you’re likely looking at a centipede. If it was slow, rounded, and had tiny legs rippling in a wave-like motion, that’s a millipede.
What Millipedes Look Like
Millipedes are brownish, elongated creatures with cylindrical or slightly flattened bodies. Adults range from half an inch to about 6.5 inches long, though most species found indoors are on the smaller end. Their defining feature is having two pairs of tiny legs per body segment (some species have four pairs), which gives them that characteristic wave-like movement as they walk. Despite the nickname “thousand-leggers,” no common household species actually has a thousand legs.
When disturbed, millipedes curl into a tight spiral. They don’t bite. Some species release a defensive liquid that can irritate your skin or sting your eyes, but this is mild and easily washed off. They are completely different from centipedes in temperament: slow, docile, and not predatory.
Millipede vs. House Centipede
These two get mixed up constantly, but they’re easy to tell apart once you know what to look for.
- Body shape: Millipedes are rounded and worm-like. Centipedes are flat.
- Legs per segment: Millipedes have two or four pairs per segment, all short and tucked close to the body. Centipedes have one pair per segment, and the legs are long and visible.
- Speed: Millipedes move slowly. House centipedes are fast runners with long legs that let them dart across walls and floors.
- Behavior when disturbed: Millipedes curl up. Centipedes sprint away.
- Biting: Millipedes don’t bite at all. Centipedes can bite when provoked, causing localized swelling and numbness.
- Diet: Millipedes eat decaying plant matter. Centipedes are predators that hunt insects, spiders, and other small arthropods.
If you’re seeing a fast, leggy creature scurrying across your bathroom floor at night, that’s almost certainly a house centipede, not a millipede.
The Most Common Indoor Species
The greenhouse millipede is the species most likely to invade homes in the eastern United States. Originally from Asia, it’s now widespread and goes by several names: garden millipede, hothouse millipede. It’s small, dark brown, and thrives in mulched flower beds and shaded areas around foundations.
What makes this species notable is its tendency to swarm. When conditions are right (or wrong, from the millipede’s perspective), thousands can migrate across lawns and into ground-level rooms. Houses on wooded lots with walkout basements or patios under upper decks are particularly vulnerable because those shaded, cool areas create ideal habitat right next to entry points.
Why They Come Inside
Millipedes need moisture and humidity to survive. They normally live outdoors in rotting leaves, decaying wood, mulch, and other damp organic matter. Two weather extremes push them indoors.
Heavy rain saturates their habitat, essentially flooding them out. When the soil and leaf litter they live in becomes waterlogged, millipedes move upward and outward, and your basement or garage happens to be in their path. On the flip side, prolonged dry conditions also trigger mass movements. Drought makes their outdoor habitat unlivable for different reasons: they dry out without sufficient moisture.
In both cases, the millipedes aren’t seeking out your home specifically. They’re fleeing unsuitable conditions and stumbling through whatever gaps they find in your foundation, door sweeps, or wall cracks.
How Long They Survive Indoors
Not long. Millipedes that end up inside your home typically survive only a few days. Indoor air is far too dry for them, and there’s nothing for them to eat. Their diet consists of decaying plant material, rotting wood, damp grass clippings, and decomposing fruit. Without access to that kind of organic matter, they starve. Some will eat houseplants or fungi if available, but most simply dehydrate.
Millipedes also don’t reproduce indoors. They lay their eggs in soil during spring, and indoor conditions don’t support egg-laying or development. So even a large invasion is a one-time wave that resolves on its own as the animals die off.
Getting Rid of Millipedes Already Inside
Because millipedes die quickly indoors, the most practical approach is simple physical removal. A vacuum (wet/dry works best) or a broom and dustpan will handle the job. Place the collected millipedes in a sealed plastic bag and toss it in an outdoor trash bin.
Spraying insecticides inside your home does very little. Even if you kill the ones already there, more keep wandering in from breeding sites outside. Indoor chemical treatment is largely a waste of time and money for this particular pest. The real solution is stopping them from getting in.
Keeping Millipedes Out
Prevention comes down to two strategies: reducing moisture near your foundation and sealing entry points.
Reduce Outdoor Habitat
Pull mulch, leaf piles, and compost away from the foundation of your home. These are the breeding sites where millipede populations build up. Manage irrigation so the soil right next to your house isn’t staying perpetually damp. Clear away stacked firewood, rotting landscape timbers, and piles of grass clippings near the building.
Seal Entry Points
Millipedes are small enough to slip through surprisingly tight gaps. Focus on these areas:
- Foundation cracks: Seal with caulk or foam.
- Door sweeps and thresholds: Install weather stripping on any exterior door, especially garage and basement doors.
- Weep holes: Block with non-toxic steel wool, then seal around it with caulk or foam.
- Pipe and vent gaps: Fill large voids around drainpipes and vents in exterior walls.
- Window and door frames: Caulk any gaps around frames.
- Baseboards: Seal cracks behind baseboards, especially in rooms where the floor gets wet, like bathrooms and laundry rooms.
This exclusion approach works better than any chemical barrier because it addresses the root problem. Millipedes breed outdoors in moist organic matter, and they’ll keep producing new generations every year. Removing their habitat near your home and blocking their path inside is the only lasting fix.