Pest library · Moisture pests
Pill bugs, sow bugs and centipedes: what moisture pests are telling you.
Roly polies in the basement, a centipede racing across the bathroom floor, silverfish in the storage room — they're all signs of the same thing: too much moisture.
- Ontario-specific identification
- Moisture fixes first
- Targeted perimeter treatment when needed
In brief
What are moisture pests?
Moisture pests are small creatures that need damp conditions to survive: pill bugs (roly polies), sow bugs, house centipedes and silverfish. They are mostly harmless, but seeing them indoors usually means there is too much humidity or a water problem in a basement, bathroom or around the foundation, so fixing the moisture is what makes them go away.
How to tell moisture pests apart
| Pest | What it looks like | Where you find it | Harmful? |
|---|---|---|---|
| Pill bug (roly poly) | Grey, armoured, about 1 cm; rolls into a ball when touched | Basements, window wells, mulch and leaf litter by the foundation | No — feeds on decaying plant matter |
| Sow bug | Like a pill bug but flatter, with two small tail-like points; can't roll up | Same as pill bugs; under boards and stones outside | No |
| House centipede | Long legs (15 pairs), fast, up to about 4 cm body | Basements, bathrooms, floor drains | Rarely bites; actually eats other insects |
| Silverfish | Silvery, teardrop-shaped, wingless, moves like a fish | Bathrooms, storage boxes, bookshelves | Damages paper, glue and fabrics; not a health risk |
Why do moisture pests come inside?
They come inside looking for damp shelter. Pill bugs and sow bugs dry out quickly, so they follow moisture through gaps in foundations and window wells; centipedes and silverfish live where humidity stays high, such as basements, bathrooms and crawl spaces.
- Mulch, leaves or firewood piled against the foundation
- Downspouts that dump water next to the house
- Basement humidity that stays above about 50%
- Leaking pipes, damp carpet or wet insulation
- Gaps under doors, around windows and where pipes enter the house
How to get rid of pill bugs, sow bugs and centipedes
Dry things out and close the way in. Run a dehumidifier to keep basement humidity below about 50%, fix leaks, pull mulch and leaf litter at least 30 cm back from the foundation, extend downspouts, and seal gaps around doors and windows. Most moisture pests disappear within a few weeks once their damp spots are gone.
- 01
Lower the humidity
Dehumidify basements and ventilate bathrooms; aim for below about 50% relative humidity.
- 02
Clear the foundation
Move mulch, leaves, stones and firewood away from the walls so the soil can dry.
- 03
Seal entry points
Weatherstrip doors, caulk gaps and fit covers on window wells.
- 04
Treat the perimeter if needed
When numbers stay high, a targeted perimeter treatment stops them crossing into the home.
When to call a professional
Call a professional when you keep finding moisture pests after drying things out, when you see them in several rooms, or when silverfish are damaging stored documents or fabrics. We inspect for the moisture source and the entry points, treat the perimeter where needed and check for other pests drawn to the same damp conditions, like carpenter ants.
Frequently asked questions
Are pill bugs harmful?
No. Pill bugs don't bite, sting or damage the house. They feed on decaying plant material and are a sign of moisture, not of a dirty home.
What's the difference between a pill bug and a sow bug?
Pill bugs roll into a tight ball when disturbed; sow bugs are flatter, have two small tail-like points and can't roll up. Both need damp conditions.
Do house centipedes bite?
Very rarely, and only if handled. A bite is comparable to a mild bee sting. House centipedes actually eat other household insects.
Will a dehumidifier get rid of silverfish?
It helps a lot. Silverfish need high humidity, so keeping it below about 50% and sealing stored paper and fabric in plastic bins usually reduces them sharply.
Get help with moisture pests
Tell us what you're finding and where. Need help right now?
Call 437 556 3606 instead- Licensed & trained professionals
- 20 years of experience
- 100% satisfaction guarantee
Moisture pests that won't go away?
We'll find the damp spot and the way in, and treat the perimeter if it's needed.