Animal · United Kingdom, Ireland, Germany
Common woodlouse
Oniscus asellus — the name this animal has in the language scientists everywhere share.
The common woodlouse is not an insect at all but a crustacean, a close relative of crabs and shrimps that has moved onto dry land. It breathes with gill-like organs under its belly, which is why it always needs somewhere damp.
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Where does the common woodlouse live?
Home: damp cellars, dead wood and stone walls.
In the wild it lives in these countries: the United Kingdom, Ireland, Germany, France, the Netherlands, Belgium, Spain, Sweden.
The short profile
Fully grown: up to about 1.5 cm long. It weighs about 0 kilograms. On the menu: plants.
The story behind it
Lift an old plank in the garden and you often find a whole crowd of woodlice pressed together in the dark. Count the legs and you get fourteen, seven pairs, which is already a clue that this is no insect. Under the tail end sit flat little plates called pleopods, and they work like gills: they only take up air when a film of water lies on them. That is the whole secret of the woodlouse. In dry air it loses water fast, so it hides by day and comes out to feed at night on dead leaves, rotting wood and mould. A mother carries her eggs in a pouch of water on her underside until the pale young crawl out, looking like miniature copies of her. Growing means moulting, and a woodlouse does it in two goes: first the back half of its armour, a few days later the front, so for a while it looks two-toned.
Find it on the globe
Common woodlouse is there as a tiny animated figure that breathes and looks around. From far away the planet is only a blue ball; detail arrives as you zoom in, and this one appears once you are close enough. Open it on the globe.
It sits at its real coordinates, not near them — the same numbers listed in the facts above. Switch off the layer for this kind of place and it disappears again; the buttons for that are down the right-hand edge.
Questions children ask
How do you tell a woodlouse from an insect?
Count the legs: a woodlouse has fourteen, an insect only six. It also has no wings, two pairs of antennae instead of one, and a body made of overlapping plates like little roof tiles.
Where do woodlice live?
Anywhere dark and damp: under stones, bark and flowerpots, in compost, in cellars and in the cracks of old walls. They are at home across Europe and have been carried to the Americas by people.
Why do woodlice need damp places?
Their breathing organs are modified gills that only work when they are wet, and their armour does not hold water in well. In a dry, heated room a woodlouse dries out within a day, so it is kindest to put one back outside under damp leaves.
Where these numbers come from
Every figure on this page was checked against public reference sources before publication. Where sources genuinely disagree, the text says so.
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