Armadillidium espanyoli is a small pill woodlouse known in the wild only from caves and the shallow underground of Castellón, in eastern Spain, and the 'Marbleized' is the pale, grey-marbled form sold under its name. Our care panel gives 18 to 26°C and 50 to 70% humidity and rates it easy. The gradient comes first: one damp end under moss, the rest of the tub drier under bark and leaf litter, air moving through, and calcium in the tub at all times. Our Armadillidium espanyoli 'Marbleized' isopods are captive-bred.
What Armadillidium espanyoli Is
Antonio Cruz, then at the University of Barcelona, described the species from animals taken in Cueva Hondera, a cave at Aín in Castellón. He named it for Francesc Español i Coll, the Catalan entomologist who collected the first animals there on 9 April 1966.
You will see the name cited as Cruz, 1990 and as Cruz, 1992. The paper appeared in volume 14 of Miscel·lània Zoològica, dated 1990, but its own header records final acceptance in July 1991, so it cannot have come out in 1990. The main taxonomic register and a 2024 key to Iberian Armadillidium both use 1992.
Cruz placed it beside the serratum group for its double-keeled head and rounded, rolling body, but its smooth, flat shell, without the group's granules and spines, keeps it from fitting fully. The species he found most like it is A. strinatii from Menorca, and the 2024 key groups the two with A. cruzi from Mallorca.
Where It Lives in the Wild
Every record we found comes from Castellón: Aín, where the type cave is, and Orpesa, where more animals were collected in 1987 in another cave, Forat d'En Ferràs. A 2021 regional review lists it from Castellón only. Cruz wrote that all its known sites are underground cavities, and a table of the region's cave endemics lists it from five cavities as an animal of the shallow underground layer, the network of cracks and spaces in broken rock just below the soil.
Cruz noted that some animals had lost part of their pigment, which he took as a sign of troglophile leanings: a troglophile can live its whole life underground but is not confined there. A seven-year logging survey of Castellón caves, published in 2024, recorded averages of about 15 to 17°C in three caves at Aín and about 20°C in one at Orpesa, most changing by under a degree through the year. None is a cave named in the species' records, and the shallow underground varies more with the seasons than a deep cave, but they show how cool and steady the ground is there.
The 'Marbleized' Form
Cruz described animals from the type cave as grey-brown with fairly obvious paler spots, and noted a tendency to lose pigment in certain populations. The animals in our photographs sit at the pale end of that: cream to off-white, with grey-brown bands and blotches across the segments and translucent edges, no two quite alike.
Most sellers call it A. espanyoli 'Marbleized', often spelt 'Marbelized'. One US seller lists it as Armadillidium cf. espanyoli and calls it the Spanish Marble, another only as an Armadillidium sp., and a Dutch breeder asks whether 'Marbleized' marks a separately developed line or is an exaggeration. We found no published identification of the hobby's stock and no account of who first kept or named the line, so we cannot say whether it was selected in captivity or came from a pale population. Our guide to isopod colours and morphs explains how pale lines arise.
Size, Shape and Eyes
Cruz measured a male at 11 mm long and 5.6 mm wide and a female at 10.2 by 5.3 mm. Our care panel gives 14 to 16 mm, a keeper's figure, and two continental breeders give about 15 mm or a little under. To check your own, measure body only, from the front of the head to the back of the last segment, leaving out the antennae.
The shell is smooth and the tail piece is a triangle with a rounded tip. Cave life has not cost it its eyes: Cruz counted 18 or 19 facets in each and called them normal, and in close-up they show as two dark spots on the head.
Setting Up the Tub
My own colonies live in 11-litre tubs, where the extra substrate and moss keep humidity and warmth steadier, though a starter group settles in something smaller if it still holds a damp end and a dry end. Our listing calls it a stay-put species; keep the lid secure all the same, since small young find gaps that adults ignore.
Lay 5 to 8 cm of flake soil, crumbled white-rotted hardwood and organic topsoil, under a deep layer of dry hardwood leaf litter, with cork bark and a flat stone or two on top. Leave coco coir out of the mix: it holds moisture but is not food, and this is an animal that eats its floor. Keep a cuttlebone or pieces of limestone in the tub at all times, since woodlice build a calcium carbonate cuticle.
Keep air moving through the tub. Stagnant, humid air kills isopods that need airflow, which we know from keeping rather than from a study, and a sealed tub soon evens out the damp-to-dry spread the setup is built on. My own tubs get two to four large vents each, with oscillating fans to keep the air moving.
Temperature and Humidity
Our care panel gives 18 to 26°C. An English home averages about 19.0°C over the heating season, October to April, 18.1°C in December and about 21.5°C in July and August, so a heated room keeps the tub in the band for most of the year with no heat mat. A room that falls below 18°C in winter wants a heat mat or heat cable on a thermostat, fixed to the side of the tub and never underneath. Our guide to heating isopods covers the kit and where the probe goes.
The band is our own figure, set cooler than most sellers' because of where the species lives. Sellers give 20 to 28°C and two continental breeders 23 to 28°C, one of them saying the animals reproduce more reliably a little warmer. Against cave averages of about 15 to 20°C, though, those top figures rest on sellers alone, so where you heat, aim for the low twenties.
Our panel gives 50 to 70% humidity, and that range covers the whole tub: the damp end under sphagnum near 70%, the bark and litter at the dry end nearer 50%. Our listing errs drier, with one damp corner, and warns against keeping it constantly wet; keepers elsewhere run anything from a quarter of the tub damp to two-thirds. Never let the damp end dry out. Start with about a third of the floor damp, watch where they gather, and widen it if they all crowd into the moss.
Feeding
Leaf litter and rotting hardwood are the staple and should always be in the tub. Add small amounts of vegetable every few days; our listing favours dried vegetable over fresh, since fresh food adds moisture this species would rather do without, and notes that pollen is taken well. Most keepers also offer a little protein once a week, a pinch of fish flakes or a dried insect. Lift anything uneaten before it moulds.
I keep tropical white springtails in with all my isopod colonies, where they graze soft mould in the damp end, though they will not rescue a tub that is too wet. Our springtail collection lists every culture we offer.
Breeding
Both sexes are needed. The female carries her fertilised eggs in a fluid-filled brood pouch, the marsupium, and the young, called mancae, leave it small and pale. Keepers, our listing included, give a gestation of about 60 days. A Dutch breeder reports small broods and puts a large, stable colony at five to six months from a starter group; a German breeder finds the young take somewhat longer to develop than in other Armadillidium.
Our listing calls it steady rather than quick: a new group takes a few weeks to settle, then builds reliably. Start with twenty or more animals if you can, as I do with my own colonies, then keep conditions steady and resist checking on them. Most woodlice live about two years, some three or four.
Behaviour and Handling
Our listing says it burrows rather than climbs. The Dutch breeder finds it mostly nocturnal, so expect to see it at dusk or when you lift the bark. Disturbed, it curls up, but into an oval rather than a sealed sphere; Cruz called its body pseudospherical. It has neither bite nor venom, so it is harmless to hold; slide a flat hand in front of it and let it walk on.
Frequently Asked Questions
How big do Armadillidium espanyoli get?
The original description measured a male at 11 mm and a female at 10.2 mm. Our care panel gives 14 to 16 mm, a keeper's figure, and continental breeders give about 15 mm or a little under.
Where do Armadillidium espanyoli come from?
Castellón, in eastern Spain. Every record we found is from caves or the shallow underground there, at Aín and Orpesa.
Is Marbleized a separate species?
Not as far as we know. 'Marbleized' is a trade name for the pale, marbled form sold as Armadillidium espanyoli, though we found no published identification of the hobby's stock. The described wild animals are grey-brown with paler spots.
Do Armadillidium espanyoli need a heat mat?
Not usually. Our panel starts at 18°C and an English home averages about 19.0°C over the heating season, so a heated room keeps it in the band for most of the year. A room that drops below 18°C in winter wants a heat mat or heat cable on a thermostat set for the low twenties, fixed to the side of the tub and never underneath.
Do Armadillidium espanyoli roll into a ball?
Yes, but not into a perfect sphere. The body is pseudospherical, so it closes into an oval ball.
Are Armadillidium espanyoli good for beginners?
Yes. Our panel rates them easy, and they suit a keeper who can hold a damp end and a dry end without over-watering. Breeding is steady rather than fast, so for a colony that fills out quickly, start with a faster species.
Where to Go From Here
For a small, pale, patterned pill woodlouse with an unusual story, the Marbleized is a rewarding one. Have the damp end and the dry end holding steady before the animals arrive. Our Armadillidium care guide explains what the rest of the genus needs, and our Armadillidium collection lists the other species we keep.
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