Porcellio succinctus 'Black Ribs' is a large, dry-country Spanish woodlouse, white with heavy dark bands across its back, and in the wild it is known from only four localities. Budde-Lund described it in 1885 from Cartagena, in Murcia, at 20 to 26mm of body length, and all four sites are in the Región de Murcia. On our care panel it wants 18 to 25°C and 45 to 55% humidity. In practice that means a dry, well-ventilated tub with one damp corner, calcium always in, and protein about twice a week. It is rated Medium. It cannot roll into a ball, it breeds slowly, it does not forgive a wet tub, and because it is known from so few wild sites, the animals in the hobby should come from captive colonies. Our Black Ribs isopods are captive-bred.
A woodlouse from four places in Murcia
Some Spanish Porcellio in the hobby range across whole regions. This one has a list of places. A 2021 review of the woodlice of Valencia and Murcia gives four localities for it: Cartagena, where Budde-Lund's series came from, Monte Roldán, the Santuario de la Fuensanta, and the Sierra de la Cresta del Gallo, all in the Región de Murcia. The same paper calls it the only woodlouse species currently known to be endemic to that region (Cifuentes, 2021).
After Budde-Lund the records are few. Dollfus listed it in 1892, Vandel wrote on its taxonomic standing in 1955, and in 2017 Garcia, Robledo and Villar Zabal published its rediscovery with a fresh description and notes for telling it apart from its relatives. It reached the trade at about the same time. A 2025 study of the trade in Spanish woodlice found it in five online shops in four varieties, at one of the highest average prices of any species in the survey (Robla and colleagues, 2025).
That study is worth knowing about if you keep this animal. It reports that P. succinctus is one of only two Spanish woodlice evaluated as Endangered, though not under IUCN criteria, and that its known populations occur only in protected areas. The authors' wider concern is that demand for rare endemic species can lead to over-collection from the wild. So the useful thing a keeper can do is buy captive-bred animals, keep each line in its own labelled tub, and never release any.
What it looks like, and how big it gets
The pattern is the point. A clean white skirt runs round the edge of the body, and across the back sit broad dark bands, brown-black in our photographs, broken by a row of pale patches down the middle. The legs, the long antennae and the long uropods at the tail are all white. Seen from above, an adult reads as black stripes on a white animal, which is where the trade name comes from.
Size depends on who is measuring and what. Budde-Lund gave the body as 20 to 26mm, not counting antennae or uropods, and our panel uses his figure. A German seller gives the body as 28mm. The 45 to 52mm you will see quoted in the trade are measured from the tips of the antennae to the tips of the uropods, or do not say how they were taken, and on this animal the appendages add a great deal. Either way it is a big woodlouse, and it moves fast when it wants to.
Young animals look nothing like their parents at first. They are almost entirely white with a few dark dots, and the bands build up over successive moults, so a settled colony shows every stage from near-white young to fully banded adults. Like every Porcellio, it cannot conglobate. It is flat-bodied and relies on speed and on wedging itself into a crevice.
Setting up the tub
This is a dry-country animal, and the main way to lose it is to keep it like a woodland isopod. Our guide to the giant Spanish Porcellio covers the group's setup in more depth; the version below is what P. succinctus needs.
Humidity: one damp corner, the rest dry
Our panel gives 45 to 55% humidity, and a Dutch breeder gives the same band and says plainly that the species cannot take high humidity. Keep one corner damp under moss and bark, roughly a fifth of the floor, and let everything else stay dry to the touch. Water the damp corner, not the tub. If the animals start sitting in the damp corner all day, the rest of the tub is too dry; if the dry end turns damp, you are watering too much or the air is not moving.
Ventilation
Give it more airflow than you would give a woodland isopod. Mesh in one side and more in the side opposite, so air moves across the tub rather than sitting behind a single vent; screw-in air vents make this easy on a plastic tub. Stagnant, humid air kills Spanish Porcellio, which I know from keeping them rather than from a study, so if in doubt, run it drier and airier.
Substrate and cover
Use a well-draining base of flake soil, white-rotted hardwood and organic topsoil. Woodlice eat their substrate, and coco coir holds moisture but is not food, so leave it out of the base. Top it with dry hardwood leaf litter, flat pieces of bark and cork for the animals to wedge under, and a little moss over the damp corner. Large flat bark on the dry side gives a big, fast animal room to spread out without crowding.
Temperature
Our panel gives 18 to 25°C. An English home averages about 19.0°C over the heating season, October to April, and about 21.5°C in July and August, so a heated room keeps the tub in band for most of the year. If the room drops below 18°C in winter, fit a heat mat or cable on a thermostat, fixed to the side of the tub and never underneath; our guide to heating isopods explains how. Heat is the bigger worry in summer. The Dutch breeder warns that too much summer heat kills this species, so keep it below about 26°C and out of the sun.
Feeding
Leaf litter and rotting hardwood are the staple, and the substrate is part of the diet. Add vegetables such as carrot, courgette or squash in small pieces, and lift whatever is left after a day.
Protein matters more for this group than for most woodlice. The Dutch breeder feeds a protein source twice a week, and that is the routine I would follow: a pinch of fish flake or a few dried calciworms on the dry side, where it will not mould. Keep calcium in permanently as cuttlebone or pieces of limestone, because a woodlouse rebuilds a calcium carbonate shell at every moult; our guide to calcium for isopods goes through the options.
Breeding
Both sexes are needed. The female carries her eggs in a brood pouch, and the young leave it as tiny white mancae with six pairs of legs, gaining the seventh over the next few moults.
In my colony, Black Ribs breed slowly, and a group builds over months rather than filling a tub. A Dutch breeder reports more than we see: once a colony is established, medium to large broods all year round with slightly fewer in winter, and young that mature in three to four months. They give a lifespan of two to two and a half years. We have found no published breeding study of the species, so treat those as one breeder's figures and plan on a slow build. What helps is stable conditions, constant calcium, regular protein and as little disturbance as you can manage: do not turn the substrate over to count young.
Keep the line pure. With four varieties in the trade and so few known wild sites behind them, mixing forms in one tub loses something that cannot easily be rebuilt.
Is it the right isopod for you?
Choose it if you have kept a dry-country Porcellio before and like the idea of a large, striking animal whose care is mostly about restraint with the water. If you have not, the Porcellio spatulatus 'Coros' is a gentler way into the dry, airy setup; our Coros care guide covers it. Skip P. succinctus if your isopods live in damp, closed tubs and you would rather keep them that way.
Frequently Asked Questions
Where do Porcellio succinctus come from?
Spain. The species is known only from the Región de Murcia, from Cartagena and three other localities in the same region, and it is described as endemic to that region. Budde-Lund's original specimens came from Cartagena.
How big do Black Ribs isopods get?
Budde-Lund measured the body at 20 to 26mm, which is the figure on our care panel. Trade figures of 45 to 52mm are tip-to-tip measurements that include the long antennae and uropods, or do not say how they were taken.
What humidity do Porcellio succinctus need?
About 45 to 55%, with one damp corner and the rest of the tub dry. They do not tolerate a wet tub, and they need strong ventilation.
Do Black Ribs isopods need a heat mat?
In a heated house, usually not, since the room sits inside the 18 to 25°C band for most of the year. If the room drops below 18°C, use a mat or cable on a thermostat, fixed to the side of the tub, and keep it below about 26°C in summer.
Is Porcellio succinctus endangered?
A 2025 study of the trade in Spanish woodlice reports it as one of only two Spanish woodlice evaluated as Endangered, though not under IUCN criteria, and says its known populations occur only in protected areas. That is why captive-bred animals are the ones to buy.
Can Porcellio succinctus roll into a ball?
No. Like all Porcellio it is flat-bodied and cannot conglobate. It runs, or wedges itself under bark.
Where to start
Set the tub up dry, with the vents in and the damp corner made, and let it run for a few days before the animals arrive. Then add them, leave them alone for a week, and keep the water to that one corner.
Leave a comment