Despite their terrestrial habits, woodlice species differ in how much humidity they need to survive. Some can live in very dry habitats, while others need a constantly high level of dampness.
There are over 45 British species of woodlice, of them I have found six locally. Here I have put together a parade which might help you identify your garden woodlice.
1. Common Pill Woodlouse, Armadillidium vulgare. Pill woodlouse are quite resistant to low humidity conditions and live in dry, sandy habitats. When disturbed they roll into a ball, protecting their legs and antennae.
2. Rough Woodlouse, Porcellio scaber. Another species that can live in relatively dry habitats, like under pots. Recognised by its matt, bumpy grey surface. They tend to grip the ground with their legs when disturbed, making it difficult to dislodge them as their flared segments form a continuous surface with the ground, and then they can walk more or less fast. Very common and often found in large aggregations in suitable habitats (top shot).
3. Smooth Woodlouse, Oniscus asellus. A large, flattened woodlice with a shiny surface. As the rough woodlice, it tends to freeze and sit tight, making it hard for predators to dislodge it from the ground, although it can also move away. It is one of the largest woodlouse species in the UK.
5. Rosy Woodlouse, Androniscus dentiger. A small species which favours damp habitats with rotting wood or organic material. Pinkish with a yellow dorsal stripe and dark contrasting eyes. It is the rarest in my garden.
6. Water Slater, Asellus aquaticus. Found in the leaf litter at the bottom of ponds. Long antennae, although many lost due to fights, then they regenerate (see photo below). Males larger than females.
A key to British woodlice by Jon Rosewell, in the iSpot resources.
Walking with Woodlice, a Natural History Museum project.
Browse BugBlog's woodlouse related posts.