Overview
The little grey armoured bugs that curl into a ball in your basement or under the patio stone are pill bugs and sowbugs — and the most useful thing to know about them is that they’re not really a pest problem at all. They’re harmless land crustaceans that live in damp soil and leaf litter, and when they turn up indoors they’re telling you something: some part of your home is holding more moisture than it should. Treat that message as the real find. Fix the damp, and the roly-polies leave with it.
Identification
Both are grey to brownish, oval, segmented, and armadillo-like, 8–18 mm long, with seven pairs of legs. The quick way to tell them apart is behaviour: the true pill bug (Armadillidium vulgare) rolls into a tight ball when touched and has a smooth rear end; the sowbug (Oniscus and Porcellio species) cannot roll up and has two small pointed tails at the back. People also confuse them with young millipedes, but millipedes are round and worm-like with far more legs.
| Feature | Pill Bug | Sowbug | Millipede |
|---|---|---|---|
| Rolls into a ball | Yes | No | No (curls flat coil) |
| Tail projections | None | Two small points | None |
| Body shape | Domed, oval | Flatter, oval | Round, elongated |
| Legs | 7 pairs | 7 pairs | Many (2 pairs/segment) |
| Group | Crustacean | Crustacean | Millipede |
Life Cycle
Females carry their eggs — and then the newly hatched young — in a fluid-filled brood pouch on the underside of the body, a crustacean trait. The young emerge as miniature versions of the adults and moult as they grow, shedding the rear half of the shell first and the front half a few days later, so a two-toned individual is simply mid-moult. They mature over several months and can live two to three years, far longer than most nuisance insects.
Habitat & Behaviour
They live outdoors in consistently damp places: under mulch, leaf litter, logs, stones, flower pots, and against foundations. They’re nocturnal, feeding at night and hiding by day, and they cannot tolerate dryness because they breathe through moist gill-like structures. That single requirement governs everything about them — they follow humidity, and a dry indoor environment kills them within days.
Diet
Pill bugs and sowbugs are decomposers. They feed on decaying leaves, mulch, rotting wood, and other organic matter, playing a genuinely useful role in breaking down debris and returning nutrients to soil. Occasionally they’ll graze on tender seedlings or ripe produce touching the ground, but they do not feed on your home, its structure, or stored pantry goods.
Signs of Infestation
- Grey roly-polies in the basement, crawlspace, or ground-floor rooms, usually near walls or under stored items.
- Dead, dried-out individuals on windowsills or basement floors — a classic sign, since they perish quickly in dry indoor air.
- Numbers spiking after heavy rain or during damp weeks, when outdoor conditions push them to migrate.
- Live ones under mulch, pots, and stones right against the foundation outside.
Damage Caused
None to your home. They don’t chew wood, damage fabrics, contaminate food, or affect building materials. In a garden they may lightly nibble seedlings and soft fruit in contact with soil, but this is minor and easily managed with mulching practices. Their real significance is diagnostic, not destructive.
Health Risks
Pill bugs and sowbugs pose no health risk. They don’t bite, sting, or transmit disease, and they’re not associated with allergies or contamination. They’re among the most benign creatures you’ll ever find indoors — the concern they raise is purely about the moisture conditions that let other, more damaging pests thrive.
Seasonal Activity in Ontario
They’re active from spring through fall outdoors. Indoor appearances cluster around wet periods: the spring melt and thaw, heavy summer rains, and damp autumn weeks. In Ontario’s freeze-thaw climate, basements and slab-on-grade rooms that stay humid can produce sightings well into the cold months. A steady indoor presence regardless of season almost always means a chronic damp area rather than seasonal weather.
Where They Hide
Outdoors: under mulch, leaf litter, logs, landscape timbers, stones, planters, and along the damp base of the foundation. Indoors: the perimeter of basements and crawlspaces, under boxes and stored goods on concrete floors, behind baseboards in damp rooms, and around floor drains and sump areas.
How They Enter Homes
They wander in at ground level through foundation cracks, gaps under doors and thresholds, utility penetrations, and unsealed basement windows — pulled in by interior humidity or pushed in by saturated soil outside. They don’t fly and don’t climb well, so entry is almost always low and close to grade.
Prevention Tips
- Lower indoor humidity — run a dehumidifier in basements and crawlspaces to well under 60%.
- Fix leaks, improve drainage, and grade soil so water flows away from the foundation.
- Pull mulch, leaf litter, and dense plantings back from directly against the house.
- Seal foundation cracks, gaps around pipes and wires, and spaces under exterior doors.
- Store boxes and firewood off the basement floor and away from damp walls.
- Ventilate closed damp rooms and repair any condensation or moisture source.
Because they need moisture to survive, a dry, sealed home is one they simply can’t occupy — the same conditions that deter silverfish and springtails. Our DIY pest prevention guide covers the whole-home moisture checklist.
DIY vs. Professional Treatment
For pill bugs and sowbugs alone, honesty comes first: you rarely need a pesticide, and spraying the ones you see solves nothing while the damp conditions remain. The fix is drying and sealing — homeowner work in most cases. Where Sani IQ adds value is diagnosis and the bigger picture. A recurring roly-poly problem often sits alongside centipedes, silverfish, or springtails feeding on the same moisture, and a technician can identify the shared source, seal the entry points, and confirm whether something more damaging is exploiting the same conditions. If we assess your home and find nothing warrants treatment, we’ll tell you so — the point of an authoritative pest company is to solve the real problem, not to sell a spray for a harmless crustacean. Our residential pest control team can take a look, and our work is backed by our Pest-Free-Or-It’s-Free guarantee.
References
- University of Kentucky Entomology — Sowbugs and Pillbugs
- Penn State Extension — Sowbugs and Pillbugs
- University of Minnesota Extension — Sowbugs and pillbugs
Last updated: July 16, 2026 · Reviewed by Sani IQ licensed technicians