Identification
Both species are small (8-15mm), grey to brownish-grey, with a segmented armoured body and seven pairs of legs (one clue they're crustaceans, not insects). Pillbugs (Armadillidium) can roll into a complete sphere when threatened — a defensive trait that gives them the nickname 'rolly polly.' Sowbugs (Oniscus, Porcellio) cannot roll completely and have two small tails (uropods) at the rear. Both are members of the order Isopoda and breathe through modified gills, which is why they require constant moisture — they desiccate and die within hours in dry conditions.
Habitat in BC
Outdoors: under rocks, in leaf litter, beneath fallen logs, in compost piles, under mulch against foundations, in damp garden bed edges. They are decomposers — their role in the ecosystem is breaking down dead plant material, and they're genuinely beneficial in the garden. Indoors: they appear only where moisture is persistent — basement perimeters, bathrooms with chronic condensation, crawlspace-adjacent rooms, beneath appliances with water leaks. BC's wet coast creates abundant outdoor habitat; the indoor migration is always a symptom of a moisture problem, never the primary pest issue.
Signs you have sowbug & pillbug
- Live sowbugs/pillbugs in basement corners, bathroom baseboards, or ground-floor laundry rooms.
- Accumulated dead shells near entry points — they desiccate quickly indoors and die within hours.
- Presence in planter pots or indoor greenery with wet soil.
- Swarming at foundation base in fall (pre-overwintering movement) or early spring (post-emergence).
Risk & damage
Zero. Sowbugs and pillbugs do not bite, sting, damage wood or fabric, carry disease, or chew indoor plants (rarely — some isopods in humid greenhouse settings nibble seedling roots, but this is uncommon in BC homes). Their presence indoors is a signal of a moisture problem — leaking downspout, grade-slope issue, crawlspace humidity, plumbing leak — and the correct intervention is moisture diagnosis, not pesticide.
Seasonality in Metro Vancouver
Active year-round in Metro Vancouver's mild climate with peak activity in spring and autumn when moisture is highest. Indoor appearances correlate strongly with heavy rain events — post-storm migrations are common in November, December, and March. Summer heat waves cause outdoor populations to move deeper into protected zones, sometimes including building envelopes.
Treatment approach
This is not a chemistry problem. Treatment is exclusively moisture management: fix the upstream water issue (leaking downspout, failed weatherproofing, plumbing leak), improve ventilation in damp spaces, and install physical barriers if needed (weatherstripping, door sweeps, foundation sealant). Chemical treatment is inappropriate — sowbugs and pillbugs are beneficial in the garden ecosystem, and any pesticide that kills them indoors will kill them outdoors too, which is not the goal. If we're called for sowbug pressure, we do a moisture audit and recommend the home improvement fix; we don't bill for chemistry that doesn't belong.
When to call a professional
Call if you can't identify the moisture source yourself, if sowbug pressure persists after obvious fixes (downspout redirect, gutter clean), or if you want a documented moisture-audit report for a real-estate disclosure or renovation decision. A moisture audit typically runs $150-$250 and includes photos, humidity readings, and recommended fixes. We rarely treat for sowbugs — we find the water problem for you.
Prevention playbook
How to prevent sowbug & pillbug in Metro Vancouver homes
- 1
Redirect downspouts
Every downspout must discharge 1.5m minimum from the foundation — 2m+ on sloped lots. This is the #1 moisture source feeding sowbug perimeter pressure on Metro Vancouver homes. A $40 downspout extension often eliminates the problem entirely.
- 2
Fix foundation grading
Soil should slope away from the foundation at 5% minimum (25mm drop per 500mm of distance). Regrade or install French drains where soil has settled toward the house over time. This is a weekend DIY project on most lots.
- 3
Replace foundation-adjacent mulch with gravel
The outer 30-45cm of perimeter should be gravel or river rock, not organic mulch. Mulch retains moisture; gravel drains. This single change materially reduces sowbug harbourage against the building.
- 4
Seal threshold gaps
Install door sweeps on all exterior ground-floor doors, caulk gaps where siding meets the foundation wall, weather-strip basement windows. Sowbugs enter through ground-level gaps less than 5mm wide.
- 5
Improve basement ventilation
Run a dehumidifier in unfinished basements (target RH <55%), ensure any crawlspace has adequate cross-ventilation and a vapour-barrier ground cover. Dry air kills isopods outright.
The Wild Pest service
See our Sowbug & Pillbug treatment page
Transparent pricing, 60-day return guarantee, same-day response across Metro Vancouver. Every treatment is documented with photos and service notes.
Frequently asked questions about sowbug & pillbug
Are sowbugs and pillbugs the same thing?+
Closely related but different species. Pillbugs (Armadillidium vulgare) can roll into a complete sphere. Sowbugs (Oniscus asellus, Porcellio scaber) cannot — they have two small tails that prevent a tight roll. Both are terrestrial crustaceans in the order Isopoda and behave similarly indoors.
Do they damage anything in a BC home?+
No. Sowbugs and pillbugs do not damage wood, fabric, drywall, food, or plants in typical home settings. They're decomposers that eat dead plant material. Their presence is a moisture indicator, not a damage cause.
Why are they in my Vancouver basement?+
Moisture. Every indoor sowbug presence traces to an exterior water source migrating inward — almost always a leaking downspout, failed foundation grading, plumbing leak, or inadequate crawlspace ventilation. Find the water, eliminate the pest.
Should I kill them?+
Indoors, physical removal is fine (vacuum or sweep). Outdoors, leave them — they're valuable decomposers that improve soil health. Spraying pesticides on an outdoor sowbug population is counterproductive ecology and does not reduce indoor pressure (that's a moisture problem).
Related species