Trachelipus difficilis Isopods for Sale

This one lives on rock. Not under bark, not in leaf litter, not in the top few centimetres of woodland soil where you find most temperate woodlice, but on stone - limestone screes, boulder fields and, now and then, the walls just inside the mouth of a cave. Slovak surveys describe it as petricolous and montane, a relic species that has held on in natural sites while the ordinary Central European woodlice spread through everything humans disturbed. Once you know that, the way it behaves in a tub makes sense.

Trachelipus difficilis was described by Radu in 1950, originally in Tracheoniscus, which is why the authority sits in brackets. Its range is Carpathian: Romania, where the type material came from, plus Hungary and Slovakia. It is not a widespread animal and there is very little of it in the global occurrence databases - a handful of records against several thousand for the common European species.

Size

Roughly 2cm, from a photograph caption in a Slovak survey of the Dobsina Ice Cave system. A caption is not a measured series, so read it as about two centimetres and not as a specification.

For scale: the 1997 revision of the European members of this genus recognised fifteen valid species, sank nineteen names into synonymy and left nine as doubtful. T. difficilis came through that process intact, which is more than can be said for several of its relatives.

The Slovak work is worth reading if you keep temperate species, because it frames this animal as a relic confined to undisturbed sites. That is unusual. Most European woodlice you can buy have done well out of human disturbance - gardens, walls, compost, rubble. This one has not, and it is a reminder that the genus contains more than the hardy generalists it is known for.

Setting up for a rock-dweller

Ours run cool, 15 to 22°C, and they do best towards the bottom of that. No heat mat. A UK room without a radiator against the wall is close to ideal, and a summer heatwave is more of a risk to this species than a cold February.

Humidity around 60 to 70% across a gradient, keeping one end of the tub damp while the far end dries out. The substrate matters less than what sits on top of it: give them flat stones, slate offcuts, pieces of limestone and overlapping bark, stacked so there are tight gaps to press into. They will use the underside of a rock in preference to a burrow every time. About 5cm of substrate underneath is plenty.

Feeding is handled by litter and white-rotted hardwood, with calcium always present. No conglobation here. This genus is built to cling, so a threatened animal presses itself flat to the rock instead of balling up, and no member of the family turns up on any published list of isopods that can. Rollers live over on the Armadillidium page.

What we cannot tell you

Not one Trachelipus has ever had its temperature or humidity tolerance tested. Every number on this page, and on every other page selling this genus, is keeper practice. Ours comes from running the animals in a UK room and watching them. It is not a measurement and will not be dressed up as one.

Colonies travel in a perforated pot bedded on moist sphagnum, inside doubled board. We post Mondays through Thursdays for delivery the next working day, add 20% to whatever you ordered, and guarantee the animals are alive on arrival. Our colony has been going here long enough to sustain itself, which is as much as we will claim about where it came from.