Pest crustacean · Armadillidium vulgare / Porcellio scaber · Last updated 14 August 2026
Woodlice
The woodlouse (Armadillidium vulgare) proliferates in damp environments — basements, crawl spaces, masonry joints. Its mass presence often indicates a structural moisture problem.
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Woodlice don't bite and don't transmit diseases, but their presence in large numbers signals a moisture or ventilation problem. They feed on decomposing organic matter. Treatment combines drying the premises with a contact insecticide in transit areas.
Identify
Signs of infestation
- Oval grey crustaceans, 10 to 18 mm, found under flowerpots, garden slabs and damp boards
- Present in damp cellar corners, under the sink, behind basement radiators
- Groups of woodlice active at night, retreating to shelter as soon as light returns
Where it's found
The woodlouse (Porcellio scaber, Armadillidium vulgare) is a terrestrial crustacean, not an insect. It only survives in areas kept above 70% relative humidity. Its presence in a building is a reliable indicator of a moisture problem: water infiltration, chronic condensation or poor drainage.
Impact
Associated risks
Moisture indicator
The woodlouse causes no direct damage to the structure. But the moisture that attracts it causes mould, peeling render and wood decay. Treating the woodlouse without treating the moisture is ineffective.
Vegetable garden damage
At high density, woodlice attack young shoots, seedlings and fruit lying on the ground (strawberries, cucumbers). Negligible impact at low density, significant in heavy infestations.
Good practice
Prevention
- 01Identify and fix the moisture source: perimeter drainage, cellar ventilation, waterproofing
- 02Keep wood, rubble and organic matter away from the building's walls
- 03Seal floor/wall joints in the cellar with hydraulic render or mortar
Frequently asked questions
What you're asking
Are woodlice dangerous?
No, woodlice don't bite, don't burrow under the skin and don't transmit diseases. But their mass presence in living spaces signals a moisture or insufficient ventilation problem worth treating at the source.
Why do I have woodlice in my basement?
Woodlice need high humidity (over 70%) to survive. A poorly ventilated basement with degraded masonry joints or rising damp is their ideal habitat. Drying the premises and a dehumidifier reduce the pressure before any treatment.
Is insecticide treatment effective against woodlice?
A contact insecticide in transit areas (skirting boards, joints, door thresholds) works short-term. For a lasting solution, the chemical treatment must be paired with structural measures: sealing cracks, improving ventilation, treating the moisture source.
Insect Control
Related pests
woodlice problem?
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