Porcellio laevis 'Grey' Isopods

Lift the bark out of a tub of these and nothing balls up. The group scatters at once, and if you pick a single animal and follow it, it does not run in a straight line. It turns, doubles back the other way, turns again, working left and right across the floor of the box as though it were solving a maze. That alternating-turn run is the entire defence of Porcellio laevis, because there is nothing else to fall back on. This species does not conglobate, as nothing in the genus can, so there is no armoured ball to roll into and sit inside while a predator loses interest. Speed and an unpredictable line are the whole plan, and swift woodlouse is one of the common names it goes by.

The name that helps more at the tub is the other one, the smooth woodlouse. Bring a light across the back and it is glossy and even, with none of the pebbled, roughened shell that Porcellio scaber carries, and in the hand that single difference tells the two species apart faster than anything else. The colouring on this listing is the wild type: grey through to a brownish-grey, plain and unmarked. Adults reach around 20mm and occasionally a little over. Males are easy to pick out once you know the tell, since they carry long, spear-shaped uropods trailing off the rear end.

The stock every other laevis came out of

This is the parent form. Every fancy P. laevis the hobby keeps was selected out of wild grey animals like these, whether that is the piebald Dairy Cow, the Giant Orange, the all-white Snow White or the Milk Back. That is the reason to buy this page's animal instead of a derived line. It is the baseline the rest were pulled out of, and it holds its own on a shelf standing next to them.

The species most likely started out in North Africa. It has been recorded in Britain since the 13th century and has since spread more or less worldwide, living under rocks and logs on damp ground and turning up readily in compost, farmyards and stables. That background shows in the temperament. It is easy, forgiving and a fair first isopod, and it is very prolific, with large broods, fast growth and sub-adults that begin breeding before they are anywhere near full size.

Setting them up

A normal UK room carries them all year, roughly 17 to 26°C, with no heat mat needed at either end of the calendar. Aim for humidity somewhere around 55 to 75 per cent and build it as a gradient, not one flat level: keep about half the floor damp, let the other half run dry, and leave the animals to choose between the two. Give the box good airflow while you are at it, since stale air sitting over damp substrate is how mould takes hold.

Go 5 to 8cm deep on the substrate so they can burrow into it, and pile dry hardwood leaf litter generously on top, because the litter is both cover and a slow background meal. Add bark for them to shelter under. Keep a calcium source in the tub at all times. Plan for the appetite as well, because this species is protein-hungry, more so than most, and a colony that is short of it will go looking elsewhere. Our Porcellio guide sets out how the genus compares, and the wider Porcellio range covers the larger species.

Groups leave here Monday to Thursday, never at the end of the week, so nothing we send sits in a depot across a weekend. A colony rides on sphagnum kept damp, in a deli tub with ventilation, packed inside an outer box built from two layers of card, tracked, on Royal Mail next-day, due before 1pm. We add spares on top of whatever count you order. Live arrival is guaranteed.