Woodlouse (sowbug, pill bug)
The woodlouse — also called a sowbug or, for the kind that rolls into a ball, a pill bug — isn't an insect but a small land crustacean, a cousin of shrimp and lobsters. Useful in the garden, where it breaks down organic matter, it becomes a nuisance once it comes indoors. Finding it in a basement, garage, bathroom or near a patio door almost always means excess moisture, poor drainage or damp debris piled against the foundation. It doesn't bite, carries no disease and damages no materials: it's a warning sign, not a danger.
Appearance
- Land crustacean about 1 to 2 cm long, with an oval, flattened, segmented body
- Grey to brownish, sometimes almost black
- Seven pairs of similar legs and two pairs of antennae, only one of which is clearly visible
- A rigid shell of jointed plates, rather like armour
- Sowbugs have two small tail appendages; pill bugs roll into a ball instead
Behaviour
- Nocturnal: it avoids light and seeks out darkness and damp
- Gathers under stones, dead wood, pots and plant debris
- Pill bugs roll into a ball when disturbed
- Does not sting, does not bite and carries no disease
- Moves slowly and dries out quickly in a dry environment
Life cycle
- Breathes through modified gills, which require constant humidity
- The female carries her eggs in a pouch on her underside, where the young develop after hatching
- Most active in spring and autumn in Quebec, during humidity peaks
- Lives in groups in damp microhabitats: crawl spaces, basements, under mulch
- Indoors, in dry air, it usually dies within a few days
Diet
- Decaying plant matter: dead leaves, rotten wood, garden debris
- Organic matter in damp soil
- Mould and waterlogged plant material
- Occasionally young shoots or ripe fruit lying on the ground
Identifying woodlice
Woodlice are isopods, crustaceans adapted to life on land. They're 1 to 2 cm long, with seven pairs of legs and an oval body made of overlapping grey or brownish plates. In Quebec you'll mainly see two kinds:
- sowbugs (such as Porcellio scaber), flatter, with two small tail appendages, which can't roll up;
- pill bugs (Armadillidium vulgare), more domed, which curl into a tight ball when disturbed — hence the nickname "roly-poly."
Both are handled the same way. They're sometimes mistaken for a silverfish (fast, silvery, with three bristles at the tail), a young cockroach (six legs, long antennae, very fast), a house centipede (long legs, very fast) or a millipede (long, cylindrical body).
Why woodlice come indoors
Woodlice breathe through modified gills that have to stay moist. They lose water quickly and die within a few days in dry air. If they're getting in, it's because they're coming from a damp spot close by — almost always outside, right against the foundation:
- thick mulch, dead leaves or soil touching the siding;
- firewood, boards, stones or planters set against the wall;
- downspouts emptying at the base of the house, or ground sloping toward the foundation;
- basement window wells full of debris.
They then crawl in under door thresholds, through foundation joints, cracks and basement windows. You'll see more of them in spring, in autumn and after heavy rain. Inside, a damp basement, a leak, a rarely used floor drain or water seepage lets them survive longer. Repeatedly finding live woodlice in one room points to a moisture source to fix, while dead, dried-out ones suggest they're simply wandering in from outside.
Are they harmful?
Woodlice don't bite or sting, don't spread disease and don't attack sound wood, food or fabrics. In the garden they may nibble seedlings or fruit lying on the soil. The real risk is indirect: the moisture that draws them in also encourages mould, wood rot and other pests such as silverfish, earwigs and house centipedes.
How to get rid of woodlice
Spraying insecticide indoors is pointless: woodlice die on their own in dry air, and more will keep coming as long as the source outside stays in place. What works, in this order:
- Dry out the inside. A dehumidifier set between 45 and 50% relative humidity in the basement, proper ventilation in bathrooms and laundry rooms, repairs to leaks and shower joints, and water poured into the traps of rarely used floor drains.
- Clear the foundation. Keep a strip of about 30 cm free of mulch, leaves and soil against the wall, raise firewood and stored items off the ground and clean out window wells.
- Move water away. Extend downspouts, correct the grading and keep gutters clear.
- Then seal up. Thresholds, door sweeps, foundation joints and window-well screens. Sealing without fixing the moisture just moves the problem elsewhere.
Vacuum up any woodlice you find. For an overview of the pests that follow moisture into a home, read our article on eliminating moisture bugs.
WHEN TO CALL EXTERMINATEK
Most woodlouse problems clear up without any chemical treatment once the environment is corrected. A professional visit becomes useful when woodlice keep coming back despite a dry basement, when they show up alongside other moisture pests (silverfish, house centipedes, earwigs), or when you can't figure out where the water is coming from.
An Exterminatek technician can confirm the cause — seepage through a crack, rising damp, poor drainage — point out the entry points to seal and, if needed, apply a targeted perimeter treatment outside. See our pest control services or contact us to talk to an expert.
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