Pill woodlouse

Pill woodlouse

Pill woodlouse ©Frank Porch

Pill woodlouse

Scientific name: Armadillidium vulgare
The defensive mechanism of the pill woodlouse is very recognisable - it curls itself into a tight ball, only showing its plated armour to its attacker. It is an important recycler of nutrients, feeding on decaying matter.

Species information


Length: 1.1-1.8cm

Conservation status


When to see

January to December


The pill woodlouse is rounded and slate grey, and when it is disturbed, it rolls up into a ball (resembling a small pill) to protect itself. It feeds on dead and decaying matter and is an important nutrient-recycler. It lives in a variety of habitats, but prefers chalk and limestone soils and turf. It emerges at night to feed and can be seen climbing trees and walls in search of mildew and rotting plants to feed on. Woodlice are actually crustaceans, not insects, so are more closely related to crabs and shrimps. They can be very numerous in compost heaps or under rocks in the garden.

How to identify

The pill woodlouse is grey and roundish, with a number of segments or 'plates' in its exoskeleton.

It looks similar to the pill millipede (Glomeris marginata), which also curls up into a ball. The best way to tell the two apart is by counting their legs: woodlice have seven pairs of walking legs, whereas pill millipedes have around 18 pairs. Another difference is that the 'plates' at the rear end of the pill woodlouse are much narrower than those on the rest of the body.


Widespread, but rarer in the north.

Did you know?

The scientific name of the pill woodlouse, Armadillidium, means 'little armadillo', and refers to the protective 'armour' and rolling behaviour of this species.

How people can help

Our gardens are a vital resource for wildlife, providing corridors of green space between open countryside, allowing species to move about. In fact, the UK's gardens provide more space for nature than all the National Nature Reserves put together. So why not try planting native plants and trees to entice birds, mammals and invertebrates into your backyard? To find out more about encouraging wildlife into your garden, visit our Wild About Gardens website: a joint initiative with the RHS, there's plenty of facts and tips to get you started.