Domestic beasts: the woodlouse

Did you know that however far inland you may live in the UK, you share your property with crustaceans?

Woodlice are isopods, which are crustaceans just like lobsters, crabs and shrimps. They originally came from the ocean, where marine isopods (some looking a lot like garden woodlice) can still be found. Look on the rocky shoreline for the sea slater – it’s the UK’s largest terrestrial isopod and the only seashore version that’s able to wander around breathing air. My pond is full of freshwater shrimps too.

These little grey things were a feature of my childhood and probably yours too – crawling around like miniature armadillos, falling off things and getting tipped upside down, wiggling pale little legs as they struggle to right themselves. Their general familiarity has led to quite fond nicknames, apparently such as chiggy pig in Devon, where I spent my formative years, and gramersow across the border in Cornwall, where I have spent the larger part of my life.

The sort that roll into a ball always surprise me, as the ones I usually see are not all that bendy and simply don’t do this. They are also less waxy. Maybe the shiny pill bug sort are a little safer from the centipedes, toads, hedgehogs and shrews on the lookout for woodlice during their nocturnal forages, in addition to its own bespoke predators, the woodlouse spider Dysdera, and the parasitic woodlouse fly. Apparently the woodlice that avoid these foes can live for four years.

Like its relative the sea slater, the woodlouse uses adapted gills for breathing air. These are fed by gases in the blood as if they are lungs, but instead of being in the chest, they are underneath and at the back, on modified hind legs. The gases diffuse through water and this is why woodlice need dampness to survive. However, their armour is not waterproof and a real soaking, as well as drying out, can kill them.

So next time you see a woodlouse, take a little time to look more closely. There are 35–40 different UK species to find, and about 3,500 woodlouse species throughout the world, so plenty to keep a woodlouse twitcher busy looking under logs and flowerpots for a long time!