Country diary: wiggling wonder of the common woodlouse

It’s not every day a woodlouse expert comes to tea. My children made a mad dash to hunt under logs in the garden to supply Beth, a soil scientist who studied woodlice at university, with specimens so she could show us how to tell males from females.

We carefully turned each woodlouse over, those little legs wiggling, and relished the new vocabulary that comes with these terrestrial isopods. They have seven pairs of pereopods, their walking legs, and five pairs of pleopods, disc-like plates on their underside that are remnants of their aquatic heritage, two of which are white and contain their gill-like lungs.

It’s surprisingly easy to work out their gender – the males have a “genital projection” aka willy (cue giggles from kids) that extends along the middle of their abdomen. The females have marsupium, brood pouches, where they place fertilised eggs to safely incubate.

Beth’s study looked at whether woodlice get lonely – or, more accurately, whether their survival rates are higher when they live in groups. She found that they function best in small social aggregations.

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As a nature writer, there can be a tendency to seek the more obscure and rare, dismissing the mundane, the easily found nearby. Yet there is a world of wonder in just this species. There are more than 30 types of woodlice in the UK and not all of them can curl into a ball. They are vital for soil health, feeding on leaf litter, decayed wood, fungi and bacteria.

Woodlouse gender ratios are a big deal too. Males that are infected with Wolbachia bacteria will become female and produce mainly female offspring, which are also infected. This is believed to happen because Wolbachia inhibits the activity of male genes.

We kept six of the common woodlice as pets, in a tank with moistened dead wood, soil and leaves, although, assured as we are of a gender mix, we are hoping for some additions to the family soon. One has just moulted, shedding its exoskeleton as it grew too big for its old armour. This came off in two sections, first the back half, then, a few days later, the front.

I’m growing oddly fond of them, yet fear their social grouping is not optimum, so will shortly be releasing them to a rotting log.