Small grey bugs shaped like armour, creeping along the bottom of basement walls or rolling into a ball when touched: those are sowbugs and pillbugs (also called woodlice). They don’t bite, don’t eat your house or food, and die quickly indoors. But if they keep coming in, they are pointing to a problem worth looking at: moisture at the base of the house.
Not an insect
Sowbugs are crustaceans, cousins of shrimp and lobsters. They breathe through structures that must stay moist: in dry air they dry out and die within days. That explains their whole behaviour.
Two kinds are found in Quebec:
- the sowbug, flattened, slate grey, with two small “tails” at the back; it can’t roll into a ball;
- the pillbug, more rounded, which rolls into a perfect ball when disturbed.
According to Health Canada, they are under 2 cm long, don’t bite, sting or transmit disease, and don’t infest food, clothing or wood.
Why they come inside
Outdoors, sowbugs live by the thousands under mulch, dead leaves, boards, stones and firewood. They feed on decaying plant matter. They get in when that habitat touches the house and water collects at the base of the wall:
- mulch and flower beds right against the foundation;
- ground sloping toward the house instead of away from it;
- clogged gutters or downspouts emptying against the wall;
- damp wooden door sills and sill plates on the ground floor;
- damp basements and crawl spaces.
They come in under doors, through foundation cracks and along pipes. Health Canada notes that a persistent indoor presence can signal a serious moisture problem.
How to get rid of them
Indoors
- Vacuum or sweep: they are slow and easy to pick up.
- A dehumidifier or small fan in damp basement corners: without moisture, the ones that got in die quickly.
- Door sweeps, and caulking along sill plates and in foundation cracks.
Insecticide indoors is pointless: Health Canada advises against it for sowbugs and pillbugs, which die on their own in a dry house.
Outdoors, where it really counts
- Clear a strip at least 30 cm wide with no mulch or leaves along the foundation; gravel works better.
- Make sure the ground slopes away from the house; regrade if needed.
- Clean gutters and extend downspouts.
- Move firewood, boards, decorative stones and pots away from the wall.
- Water in the morning rather than the evening, so the soil dries before night.
When to call
- You find them indoors every day, even after clearing the foundation.
- They show up in one specific spot on the floor or wall: there may be damp wood or a leak.
- They arrive along with earwigs and house centipedes: the base of the house is too damp.
A technician finds the entry points and damp areas and, if needed, applies an exterior treatment along the foundation. For an assessment, contact us or call 514-638-8705. The estimate is free.
Not sure what you found? Our guide to bugs in the house in Quebec helps you identify it by where and when you see it.
Frequently asked questions
Can sowbugs breed inside the house?
Only somewhere truly damp: a wet crawl space, a basement with a leak. That in itself is the sign there is a problem to fix.
Why do I find them dead on the floor?
They came in, found no moisture and dried out. Lots of dead sowbugs means lots of live ones just outside.
Do they eat plants?
Mostly decaying matter. They may nibble seedlings and fruit lying on the ground, but rarely do serious damage.