Porcellio expansus 'La Sénia' Isopods

Same species, biggest form. Where the orange expansus is grown for colour, the La Sénia locale is the one grown for sheer size, and it is one of the largest woodlice you can keep. Sold as the Giant Spanish Isopod or simply Giant Expansus, Porcellio expansus 'La Sénia' is the largest-growing locale of the species, collected from around the town of La Sénia in northeastern Spain. If you already know the vivid orange form of the same species, think of this as its heavyweight cousin: the same animal, selected for bulk rather than brightness.

Mature adults reach around 4 to 5cm, which puts a full-grown specimen at roughly the size of a matchbox. The carapace is broad and flared at the edges, dark and heavy-looking, and there is real weight behind those legs when one walks across the substrate. This is a display giant in its own right rather than a background cleanup crew, an animal you build a tank around and actually watch. It sits at the very top of the giant-Porcellio tier alongside the Titan (P. hoffmannseggii) and Porcellio magnificus, and it grows larger than the standard orange form. Like all Porcellio, it cannot fully conglobate; it is simply too large and too flat to roll into a complete ball, relying instead on its size and cover.

The reason to keep one is presence. Smaller isopods are animals you glimpse now and then as they work; a La Sénia colony gives you scale and intent, individuals moving across the leaf litter with a deliberate, unhurried gait that is worth watching in its own right. They anchor a large arid display and hold their own as the feature of an enclosure rather than the workforce hidden beneath it.

Care is the dry, giant-Porcellio routine, and it earns its Medium rating mainly through scale rather than fuss. Warm room temperature suits their northeastern-Spanish origins, and the key is to keep them on the drier side with a moisture gradient: aim for around 50 to 60% overall with a single damp corner they can visit, not constant high humidity, which is the mistake most likely to cost you animals. Pair that with good, generous ventilation. Give them a deep substrate, since a large woodlouse of this kind is a serious burrower; something rich like flake soil with plenty of rotting hardwood works well, topped with a deep layer of magnolia leaves and other leaf litter. Keep high calcium available at all times, because moulting a 5cm exoskeleton is a demanding job, and offer regular protein alongside the wood and leaves. A modest springtail culture tucked into the damp corner will handle mould around fresh food without needing the humidity to climb.

Give them room. Large males can be territorial, so space and well-spaced hides matter more here than with the weedy species, letting individuals settle without constant confrontation. Breeding is slower and more of a project than the prolific isopods, with smaller broods and a longer wait to maturity, so treat a settled, growing colony as the reward rather than expecting a population explosion. The larger, hardier juveniles do help once things get going. To see where this locale fits, browse the wider Porcellio collection or read our guide to the different types of Porcellio isopods.

Every colony leaves here captive-bred and packed to travel, settled into a ventilated tub of damp sphagnum inside a double-walled box for insulation. We dispatch Monday to Thursday by tracked next-day Royal Mail, aiming for delivery by 1pm, and every order is covered by our live-arrival guarantee. We include a small overcount as standard, so you should find a few extra in the tub.