- Scientific name
- Armadillidium vulgare
- Also called
- roly-poly, sowbug, woodlouse
- Size
- About 1/4–1/2 in
- Color
- Slate gray to brownish
- Found in
- Mulch, under pots and stones, damp basements and garages
- Harmful?
- No. May nibble seedlings
- Active
- Spring to fall, at night
Pill bugs, or roly-polies, aren’t insects but land-dwelling crustaceans related to shrimp and crabs. They’re completely harmless, and finding them indoors usually points to dampness or a gap under a door. The one thing to do: keep mulch and leaf litter back from the foundation and seal gaps under doors.
This page covers how to identify pill bugs, tell them from sowbugs and millipedes, and why they come inside. It rests on University of Kentucky guidance.
How to Identify a Pill Bug: Armored and Rolls Up
- Oval, segmented, armored body, about 1/4 to 1/2 inch, rarely more than 3/4 inch, slate gray.
- Seven pairs of legs under seven overlapping plates.
- Rolls into a tight ball when touched, which is where “roly-poly” comes from. Rolling up also helps it hold in water.
Pill bugs bunched together under bark. Damp, dark spots like this are where they gather. Photo: Michel Langeveld (CC BY-SA 4.0), via Wikimedia Commons.
Pill Bug vs. Look-Alikes: Ball or No Ball
| Creature | How it differs | How to tell |
|---|---|---|
| Pill bug | Rolls into a ball | No visible tail points |
| Sowbug | Can’t roll up | Two small tail-like points at the back |
| Millipede | Long and worm-like | Many legs; coils into a spiral |
Pill bugs and sowbugs live in the same places and are handled the same way.
Why Pill Bugs Come Inside: They Need Moisture
They depend on humid surroundings to survive, so they’re mostly active at night and live in damp spots. That need for moisture can drive them into crawl spaces, basements and ground-floor rooms. The University of Kentucky says frequent pill bugs indoors may signal a moisture problem or a gap around a window or door. Indoors they dry out and die within a day or two.
Where You’ll Find Them: Under Damp Cover
- Under mulch, leaves, stones, boards and flower pots
- Along foundations, patios and in window wells
- Damp basements, garages and ground-floor rooms near doors
Other moisture-loving visitors, such as springtails and earwigs, turn up in the same damp spots.
Are Pill Bugs Harmful? No
They don’t bite, sting or damage homes. Outdoors they mostly eat decaying plant material, and occasionally nibble seedlings, roots and low-hanging strawberries.
How to Confirm It’s a Pill Bug
- Touch it: a pill bug rolls into a ball; a sowbug can’t.
- Count the legs: seven pairs.
- Look under nearby mulch, pots or boards for more.
What to Do: Dry Out and Seal Up
Keep mulch and leaf litter back from the foundation, move pots and boards, fix drainage and seal gaps under doors and around windows. Sweep up the ones that get in. For other pests, browse all pest guides.
Often confused with
Sources
Last reviewed Oct 4, 2026.
