Woodlice

My latest "Nature Notes" . . .

When I was a boy, I was always fascinated by what today’s kids call “minibeasts” - and woodlice were among my favourites.  My apologies to those of you who hate them, but I’m going to write about them this month, because I still find them very interesting, and maybe you will too, for they are in some ways quite amazing little animals, and harmless to human beings.  I am told in fact that they are quite good eating, related as they are to shrimps and prawns, but I have never put this to the test and have no intention of doing so!  Of the 3,500 or so species of Woodlice in the world, most are vegetarian, including all the 35 to 40 species found in the UK.

Should you wish to keep a woodlouse as a pet, I’m told they do well in margarine tubs, being unable to climb up the sides and escape.  They need damp conditions, so some damp soil on the bottom is good, with something to hide under (they like the dark), and a few vegetable scraps from time to time for them to eat. 

Woodlice have seven pairs of legs, and are Crustaceans, more closely related to crabs and prawns than to (say) insects or spiders. In fact they are virtually the only Crustaceans to live on land with any great success.  They breathe through lungs found towards the back of the body, on the underside.

Baby woodlice have only six pairs of legs, and spend the first part of their lives in a brood pouch, or marsupium, underneath the mother, leaving after the first moult when the seventh pair of legs has been gained. There can be quite large numbers of young, which appear to be “born” as tiny white versions of the adults, thanks to the time spent in the marsupium.  The number born increases with the size of the adult, but broods of more than 200 have been recorded (obviously, by no means all of these will survive to adulthood). Most British species have one brood per year.

Almost all our woodlouse species feed on dead leaves and other rotting vegetation, including old wood.  The largest British woodlouse, the Sea Slater, lives on seaweed - it can grow to about an inch long (worth looking for when at the seaside).  The Ant Woodlouse has a strange lifestyle:  it is white, blind, and lives entirely in ant nests feeding on the ant droppings and associated fungi. 

Like insects, woodlice need to moult in order to grow, but unusually they shed only half their skin at a time - the back half first, then a few days later the front.  Woodlice often eat their shed skin, and this is a time when they are especially vulnerable to predators.  Woodlice are readily eaten by shrews and by insectivorous birds, and at least one British species of spider is a woodlouse specialist.