Trachelipus trilobatus 'Trilobite' Isopods

Most keepers walk straight past the Trachelipus shelf on the way to something brighter, and the Trilobite Isopod is the species that makes them stop and come back. Trachelipus trilobatus earns its nickname: a wide, flattened, heavily segmented body that reads like something pressed out of a slab of shale. The three lobes of the species name are on the head rather than the tail, where a well-developed median lobe sits between two lateral ones, while the pleotelson behind tapers to a sharp point. The colour is understated, a solid grey to charcoal with a faint warm ring rather than any loud pattern, which only makes the fossil-like shape stand out more. If you like form over flash, this one rewards a closer look.

It is also refreshingly easy. Behind the prehistoric silhouette sits a hardy, adaptable, quick-breeding woodlouse that asks very little. As a temperate species of the Banat and the southern Carpathians in south-west Romania, which is where hobby stock comes from, it takes cool household conditions in its stride and never needs heating in a normal UK home. It sits alongside its lesser-seen genus-mates, the cold-tolerant Trachelipus caucasius, the neat Trachelipus mostarensis and the aptly named Trachelipus difficilis, in a corner of the hobby that deserves more attention than it gets. Our Trachelipus care guide covers all six of them together.

On size, expect a medium woodlouse. Measured Romanian specimens run to 18 by 11 mm in males and 19 by 12 mm in females, so 19 mm is the honest ceiling; the 24 mm this page carried until September 2026 came from the hobby and is not supported by any measured series. In flat, shield-shaped outline it recalls the dry-country Coros (Porcellio spatulatus), though the Trilobite is smaller, darker and solid-toned. One thing it shares with the rest of its genus: it cannot pull the full pill-bug trick. Where a true Armadillidium seals into a ball, Trachelipus stays flat and instead relies on that low profile, a quick turn of speed and a good hiding place.

Set them up in a five to ten litre tub with a secure lid and cross-ventilation on opposite walls. They like it a touch damper than the dry-Mediterranean Porcellio but nowhere near tropical, so aim for a moderate humidity around 55 to 70% with a gradient: a damp corner under sphagnum and leaf litter, the rest allowed to breathe and dry between mistings. Room temperature anywhere from about 15 to 26°C keeps them active, and a shaded spot away from radiators and windows keeps that range steady.

For substrate, build a living base of flake soil, well-rotted hardwood and organic topsoil around five centimetres deep. As with most detritivores I would avoid a straight coco-coir base, which retains moisture but offers nothing to graze; the wood-and-leaf mix feeds them as it breaks down. Layer magnolia and oak leaf litter over the top with cork bark and a few chunks of rotting wood for cover, and keep a calcium source such as cuttlebone or crushed shell available throughout for healthy moults.

Diet is the usual detritivore spread and no trouble at all. Leaf litter and decaying wood form the constant base; supplement with soft vegetables like courgette, carrot and squash a couple of times a week, remove leftovers before they spoil, and offer a modest pinch of protein such as fish flake or dried insects now and then to keep a breeding group ticking over. They are prolific once settled, the female carrying young in her pouch and releasing live miniatures, and a starter colony given warmth, food and calcium builds steadily into a self-sustaining population within a season or two.

A springtail culture alongside them grazes the soft mould around damp corners and protein scraps, and the two coexist without any bother. Every order travels as an established colony in a double-walled box around a ventilated tub of damp sphagnum, posted Monday to Thursday by tracked Royal Mail aiming for next-day delivery, packed with care and covered by our live-arrival guarantee.