Armadillidium serratum 'Hedgehog' Isopods

We already keep a small, heavily armoured pill woodlouse: the Crystal Pineapple. Armadillidium serratum is the same idea at a size you can actually see, and that size is the whole reason to bother with it. On the Pineapple the sculpting is real but miniature, and you have to get close, or reach for a hand lens, to see what the shell is actually doing. Scale the animal up and the same architecture becomes something you can read from across the room, with every raised point and ridge sitting out in plain view.

Budde-Lund described the species in 1885 and that name is the accepted one, though it has also appeared in places as Armadillidium spinosum. The epithet comes from the Latin serratus, meaning saw-toothed, which is a fair account of the edges. In the trade it is sold as the Hedgehog Isopod, and nobody appears to have written down where that name came from. The shell is strongly tuberculate, spiky and raised all over instead of smooth, with the points concentrated along the back.

Published size figures for this species disagree with each other, so the honest summary is small to medium for the genus, and noticeably bigger than the Crystal Pineapple. That gap is what makes the texture worth looking at. It is a Mediterranean animal, recorded from France and Spain, and it balls up the way every true pill woodlouse does. Unlike the smooth-shelled species in the genus, the texture does not vanish when it closes up, so a balled serratum still reads as a spiky object rather than a bead.

Mediterranean, not tropical

A range of 18 to 26°C covers it, and that is UK room temperature year round, so nothing needs heating in a normally warm house. Humidity should sit in the middle, somewhere around 50 to 65 per cent, and it wants to be a gradient, not an even damp. Keep one end moist and let the far end dry out between waterings, then leave the animals to pick their spot. Pair that with medium airflow. This is a drier, better-aired setup than the tropical species most general care advice is written around, and a stuffy wet box is the quickest way to lose a group.

Deep litter and a constant calcium supply

A nutritious base substrate does the heavy lifting, topped with a generous covering of dry hardwood leaf litter and plenty of bark to shelter under and clamp against. That litter is the standing meal the colony grazes on between feeds, so keep it deep and keep replacing it. A permanent calcium source matters more here than in most tubs, because a heavily sculpted shell takes a lot of building and rebuilding. Cuttlebone or crushed shell stays in the enclosure permanently, not as an occasional top-up. Vegetables are taken readily, and an occasional protein offering supports breeding.

Care is easy, which is the useful thing about it, because rarity in this hobby usually arrives attached to a demanding care sheet. This species is uncommon and still undemanding. Anyone already running a drier Armadillidium tub can add it without changing a thing, so a newer keeper can take one on without a steep learning curve. If you are assembling a shelf of textured pill woodlice, Beier's Pill Woodlouse is the spiny Greek endemic, Armadillidium peraccae is the bumpy one kept drier still, and Armadillidium granulatum brings a pebbled finish. For the smooth, patterned counterpoint, the Zebra is where most people begin with the genus. Our Armadillidium care guide goes into the husbandry, and the wider Armadillidium range holds the rest.

Packing is a ventilated deli tub, sphagnum damp beneath the animals, and two thicknesses of card around all of it. We post Monday to Thursday and stop there, next-day and tracked through Royal Mail, before 1pm, which is what stops a box of ours sitting out a Saturday. A few spares travel above the number ordered. Live arrival is covered.