Few household pests cause as much alarm for so little actual harm as millipedes and centipedes. A dozen leggy bodies crawling across a basement wall sends most people reaching for a spray can, yet neither pest damages wood, wiring, or food. Millipedes feed on decaying plant matter, and centipedes hunt other insects. Both wander indoors when outdoor conditions turn hostile, after heavy rain, during drought, or in a cold snap, and both die quickly inside a dry house. That last fact is the key to control: pests follow moisture, and shaping the environment to discourage them works the same way as controlling traffic speed on a street, where the roadway is designed to slow movement. Remove the moisture and the hiding places, and the invasion ends on its own.
Centipedes and millipedes are easy to confuse but behave differently. Centipedes have one pair of legs per body segment, flat bodies, and move fast to catch prey; a bite from a large house centipede is painful but rare. Millipedes have two pairs of legs per segment, rounded bodies, and crawl slowly; they defend themselves by curling up and releasing an irritating fluid. Knowing which one you have changes the cleanup routine, because centipedes need a food supply of other insects while millipedes only need damp organic matter. A single centipede can lay dozens of eggs in a damp basement over a season, which is why one sighting often means many more are hidden.
Moisture Is the Magnet
Both pests require high humidity to survive. Millipedes dry out within hours indoors, which is why they show up in bathrooms, laundry rooms, and basements after heavy rain. Centipedes tolerate drier air but still prefer damp spots under sinks and around drains. A dehumidifier that holds indoor humidity between 40 and 50 percent makes most of the house uninhabitable for them. The same moisture discipline used when controlling spa room moisture in a finished basement applies here: fix leaks, ventilate enclosed spaces, and dry standing water within 24 hours.
Where moisture collects unnoticed
- Crawl spaces with exposed soil and no vapor barrier
- Leaky hose bibs and outdoor spigots that wet foundation walls
- Clogged gutters that spill water against the siding
- Condensate lines from air conditioners and dehumidifiers
- Damp cardboard boxes stored on concrete floors
Measure before you guess
A $15 hygrometer removes the guesswork. Check each room at floor level, where both pests travel. Readings above 60 percent humidity feed the problem; below 50 percent, millipedes stop surviving long enough to reproduce indoors. Run a dehumidifier in the wettest zone and empty it on a schedule, because a full tank stops working overnight. Vent the dryer to the outside and run the bathroom exhaust fan for 20 minutes after every shower, because steam from a single shower adds about a pint of moisture to the air.
Remove What You See, Then Find the Rest
Sweep or vacuum the pests you find, then look for the source. Vacuuming is the fastest removal method for both creatures, and it picks up eggs and shed skins too. Dispose of the bag outside so the contents cannot crawl back out. Sticking to a removal schedule takes the same vigilance as controlling subcontractor price creep on a renovation: the job only gets harder the longer it is ignored, and a weekly sweep of basement corners catches new arrivals before they settle in.
- Vacuum every visible millipede and centipede, including window sills and baseboards.
- Move boxes, firewood, and clutter away from walls and off the floor.
- Wipe damp surfaces dry and mop with a cleaning solution to remove scent trails.
- Set glue boards along baseboards in the worst rooms to monitor activity for a week.
- Repeat the vacuum pass daily for three days, then weekly until the count drops to zero.
Sweep the perimeter
Outdoor cleanup matters as much as indoor removal. Rake leaves, grass clippings, and mulch away from the foundation so they do not hold moisture against the wall. Keep firewood stacked off the ground and away from the house. Trim shrubs so sunlight reaches the soil and dries it out, because a shaded, mulched bed is a millipede nursery.
Seal the Entry Points
Sealing is the permanent half of the solution. Millipedes and centipedes squeeze through gaps a quarter-inch wide, so the building envelope has to be tighter than it looks. Walk the foundation and check every penetration: utility lines, hose bibs, vents, and the sill plate. The same joint design thinking used for controlling cracking in concrete structures applies here: gaps are managed at the joint, not patched later, so foundation cracks should be sealed while they are still hairline. Use exterior-grade caulk for small cracks and expanding foam for larger openings, then re-check after a season.
| Entry point | Typical gap | Seal with |
|---|---|---|
| Foundation cracks | 1/16 to 1/4 inch | Polyurethane caulk or hydraulic cement |
| Door thresholds | 1/4 to 1/2 inch | Door sweep and weatherstripping |
| Window frames | 1/8 to 1/4 inch | Exterior caulk; replace rotted sills |
| Utility penetrations | 1/2 inch or more | Expanding foam, then caulk over the top |
| Vents and louvers | 1/4 inch or more | Screen mesh over the opening |
| Garage door edges | Up to 1/2 inch | Rubber bottom seal |
Check the basement windows
Basement window wells collect leaves and water, and the frames rot quietly. Clear the wells, replace cracked panes, and make sure each window closes fully. A missing screen on a basement window is an open door for both pests. Run a finger along the frame seam on a windy day; if you feel a draft, caulk it. Seal the top of the frame too, because water that runs down the wall above a window finds the smallest opening.
Dry Out the Damp Zones
After sealing, attack the humidity sources that keep drawing pests in. Fix dripping faucets, wrap cold water pipes that sweat in summer, and slope the grading away from the foundation so rain runs off instead of pooling. Homeowners use the same essential strategies for homeowners and builders that keep spa rooms from growing mold: exhaust moist air, insulate cold surfaces, and run a small dehumidifier in the wettest area until the problem clears.
Grading and drainage fixes
- Add 6 inches of slope away from the foundation over the first 10 feet
- Extend downspouts at least 6 feet from the wall
- Install a vapor barrier over exposed crawl space soil
- Vent crawl spaces in summer and close the vents in winter
- Repair leaking irrigation lines near the house
Size the dehumidifier to the room
Pick the dehumidifier by room size, not price. A 30-pint unit handles a typical basement of 800 to 1,000 square feet, while a 50-pint unit covers up to 1,500 square feet. Set the target at 45 percent, empty the tank before it fills, and clean the filter monthly, because a clogged coil pushes humidity back into the room.
Reduce the Insect Food Supply
Centipedes stay only where prey is abundant. Cut the food supply and the population collapses, which means controlling the other household insects, ants, silverfish, and small flies, that make up the centipede diet. Pest-proofing overlaps with air quality work because both depend on the building envelope; the same mechanical ventilation guide used for controlling indoor air quality shows how continuous air exchange dries out the hidden corners where insects breed. A tighter, drier house supports fewer insects of every kind. Pay attention to the kitchen and bath, because crumbs and standing water in those rooms feed the small prey that centipedes eat.
Break the indoor insect cycle
- Store pet food in sealed containers and do not leave bowls out overnight.
- Take out trash and compost regularly, and keep the bins covered.
- Fix leaking pipes and faucets that feed damp-loving insects.
- Vacuum under appliances and along baseboards monthly.
- Check houseplants, because overwatered pots breed fungus gnats.
Keep the Perimeter Defense Going
Pest control in a house is not a one-time event. Rainy seasons bring new waves of millipedes, and centipede populations rebuild from eggs laid in wall voids. A short quarterly checklist keeps the defense current: re-caulk new cracks, confirm the dehumidifier still works, and clear leaves before fall rains. Budgeting for these small tasks is the same discipline as controlling sales and marketing costs in home building: small, regular payments beat a large emergency bill. Most homes end the problem with caulk, a dehumidifier, and a vacuum, without a single pesticide application. If an infestation persists after two seasons of sealing and drying, look for a hidden moisture source: a leaking sewer line, a damp wall cavity, or a broken sprinkler head under the foundation.
Quarterly prevention checklist
- Walk the foundation and seal new cracks in spring and fall
- Test basement humidity and reset the dehumidifier target
- Clear gutters and downspouts before heavy rain seasons
- Inspect door sweeps and window screens for damage
- Move stored items off basement floors and rotate them