Regular readers will know I photograph pond creatures on a fairly regular basis, but up until today I have never managed a shot I’m happy with of a Water louse Asellus aquaticus. I catch them on most pond dips, but because they are so common, combined with the fact they have the habit tucking themselves in to aquarium corners or under leaves and weed, I’ve rarely bothered to try photograph them, and failed when I have tried. Today however I got these shots.
Water lice are fascinating creatures. Also called water slaters or water hog-louse, their resemblance to woodlice is not a coincidence as they both types of isopod, a group of crustaceans. This means they are more closely related to crabs and lobsters than the insects like water boatman and dragonfly larvae with which they share the pond.
You can often find them in pairs, with the larger male over the top of a smaller female.
He is guarding her from other males and waiting for her to moult, as this the only time he can mate with her. Like woodlice they moult their exoskeleton in two halves, the posterior (rear) half first and the anterior (front) half second. He will continue guard her after mating until her exoskeleton hardens after the moult and no other male can mate with her.