Woodlice identification and control

How to identify a woodlouse

Woodlice (also called slaters, cheesy bugs or pill bugs) are small crustaceans, related to crabs and shrimps. BPCA describes them as oval, grey and segmented, 10 to 15 mm long, with 14 legs and prominent feelers. The RHS says they typically measure up to 1 cm and can have yellow or pinkish-brown markings. There are around 30 species in Britain, five of which are often found in gardens.

The pill woodlouse can roll into a ball when disturbed. The common species cannot, and just runs for cover.

Lookalikes

• Pill millipedes also roll into a ball but have many more legs and a smooth, shiny, domed shell.
• Small beetles have six legs and hard wing cases.
• Woodlouse spiders are the pinkish-brown spiders with a large red-orange body that hunt woodlice, so seeing one often means you have plenty of them.

Why they are indoors, and are they harmful?

Woodlice breathe through gill-like structures and dry out quickly, so they need moisture. They hide in dark, damp places by day and feed at night on decaying plant matter. Indoors, that usually means a damp ground-floor room, a leaking pipe, a basement, a conservatory or a gap under an external door.

They do not bite, sting or spread disease, and they cannot damage the structure of a home. The RHS says they are largely beneficial in the garden, recycling decaying matter, though they can occasionally damage seedlings and strawberries. A woodlouse indoors is a clue about moisture, not a threat.

How to get rid of them

BPCA says no treatment is normally necessary and the cure is to put right any dampness.

• Repair leaks and improve ventilation.
• Clear leaf litter, rotting wood and plant debris from along the foot of walls.
• Make sure air bricks are clear and the ground outside slopes away from the house.
• Seal gaps under doors and at thresholds.
• Sweep up the ones that get in and put them outside.

If they persist, BPCA suggests an insecticidal powder or long-lasting spray around thresholds and entry points, used strictly as the label says.

When a professional is worth it

Very rarely. If you are finding woodlice in large numbers inside, the underlying problem is nearly always damp, and a builder, plumber or damp specialist is more useful than a pest controller. Call a pest firm only if the numbers do not fall after the damp is fixed, and ask them to treat entry points, not the whole house.