Woodlouse or Waterlouse?

by Mike Morgan

If you look under a stone in the garden, it is very likely you will find a woodlouse. These are one of the few Crustacea which are land animals. They have relatives which may be found at the seashore or in freshwater. The waterlouse is very common in freshwater, i.e. ponds or slow-moving streams.

A waterlouse (Asellus) is shown on the right , and in appearance looks just like an ordinary woodlouse. There are characteristics which help to distinguish the two. If you look at a waterlouse, having placed it on its back, note how the body is flat compared with its depth. Also compare the legs and antennae . These are much longer than seen in the wood-louse.

Asellus lives very well in an aquarium among water-weed. This is an ideal specimen to keep, to demonstrate crustacean characters. They breed readily, the females laying their eggs about April or May.

If the females carrying eggs or young are isolated in a petri dish, these can be observed until the young are set free. These are interesting in that there is no pigment in the skin. This makes the young one of the best specimens to observe the circulation of blood in the Crustacea. Individual corpuscles can be seen circulating and the contractions of the heart can be watched, before the development of pigment in the skin of the adult.

This is a lovely experiment for interested kids to do. Similar to watching the heartbeat and circulation in Daphnia.

Editor's Note: This article by Ron Neumeyer also shows a woodlouse.


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