Harmless

Greenhouse millipede

Oxidus gracilis

Also called garden millipede, flat-backed millipede, hothouse millipede

Greenhouse millipedes do not bite or sting; they can give off a smelly defensive fluid when handled, so pick them up with a tissue or sweep them up.

Photo: capacoscar, CC BY 4.0, via iNaturalist

SizeAbout 16–25 mm (5/8 to 1 inch)

Where in the houseBasement, garage, bathroom, living room, outside near the house

WhenSummer and fall, especially after heavy rains; spring migrations also happen. They are mostly inactive in winter.

Check these features

Long, slightly flattened body made of many segments
Reddish brown to dark brown on top, paler on the sides and underneath
Two pairs of short legs on most body segments
Slow crawler that curls up or goes still when touched
Often shows up in large groups after heavy rain

Bites and stings

Does not bite people. When handled it may release a smelly defensive fluid that can stain or briefly irritate skin; wash your hands with soap and water after touching one, and keep it away from your eyes.

What to do

Sweep or vacuum up millipedes you find indoors; they will die on their own in dry indoor air.
If you touch one, wash your hands, and avoid rubbing your eyes.
Put sticky traps across doorways and basement entry points to catch ones coming in during a migration.
Outdoors, sweep dead millipedes off patios and walks; indoor sprays add little.

Look-alikes

House centipede and other centipedesCentipedes are fast, have one pair of longer legs per segment and long antennae, and can bite, while millipedes are slow, have two pairs of short legs per segment and do not bite.

Wireworms and caterpillarsWireworms and caterpillars have only a few legs near the front (plus stubby false legs on caterpillars), while a millipede has legs along its whole body.

Why it came inside

Greenhouse millipedes build up in mulch, leaf litter, compost and lawn thatch, and heavy rain or drought drives large numbers to wander onto patios and into homes through door gaps and foundation cracks; indoor air is too dry for them, so most die within a short time.

Keep it out

Rake mulch, grass clippings and leaf litter back from the foundation, or use gravel next to the house.
Install door sweeps and tight weatherstripping, and seal foundation cracks and weep-hole gaps.
Fix drainage so rainwater does not soak the soil next to the house.
Run a dehumidifier in damp basements and keep window wells clear of debris.

What helps

Links go to Amazon search results so you can compare current options. As an Amazon Associate I earn from qualifying purchases. Always follow the product label.

Door sweep

Closes the gap under an exterior door. If you can see daylight under the door, bugs can get in.

See options on Amazon

Weatherstripping

Seals the gaps around doors and windows that let in drafts and bugs alike.

See options on Amazon

Caulk and sealant

Silicone or siliconized acrylic caulk closes cracks around windows, pipes and baseboards. Bigger gaps need foam backer rod or expanding foam first.

See options on Amazon

Sticky traps

Flat glue traps set along walls and in corners show what is moving through and where. Place them where pets and children can't reach.

See options on Amazon

Dehumidifier

Keeping a basement at about 50 percent humidity or lower makes it less welcoming to the bugs that need damp air.

See options on Amazon

Vacuum with a hose

Lets you remove bugs, webs and egg sacs without touching them. Empty the bag or canister outside right away.

See options on Amazon

Screen repair kit

Patches or replaces torn window and door screens, one of the most common ways insects get in.

See options on Amazon

Sources

Checked October 18, 2026. Rating backed by 4 sources. How we rate danger.