A raised plate on the forehead, a measured 21.5 mm and an Orange line that is one of the brightest in the hobby: Armadillidium pallasii is the big Adriatic and Black Sea pill woodlouse that part of the UK trade still sells as the Rhino Horned Roller. It is an easy species once it has settled: a heated room at 18 to 26°C, a tub that is mostly dry with one damp end, deep leaf litter and rotted wood, calcium within reach, a little more protein than a small isopod would get, and a starting group of twenty or more. What follows is the published record, the trade's figures held up against it, and the way we keep our own colonies.
Which Species It Is
Johann Friedrich Brandt named Armadillidium pallasii in 1833 in a single line of Latin: a granular, grey, unspotted back, a very long frontal plate, and a locality. For the locality he wrote Crimea, then put a question mark after it, and the question mark has never gone away. When Helmut Schmalfuss re-examined Brandt's specimens for his 2011 revision of the Armadillidium of the Ionian islands, he fixed one as the lectotype and noted that the label may be a mistake, because the animals look Dalmatian, though the species is recorded in Crimea all the same. The name almost certainly honours Peter Simon Pallas, though Brandt did not say so.
Three later names turned out to be the same animal: Budde-Lund's A. frontirostre of 1885, described from museum animals labelled Trieste, Rome and Ischia, the last two well to the west of the range Schmalfuss now accepts; Verhoeff's A. frontisignum of 1901, from a single 11 mm male in southern Herzegovina; and Strouhal's A. pallasii garganum of 1937, named for the Gargano. Schmalfuss sank all three in 2011 after comparing them with Brandt's types. Part of the UK trade still sells this species as the Rhino Horned Roller under the name frontirostre, often misspelt; the horn is the frontal plate.
One split went the other way: Armadillidium peraccae, which we also keep, was lumped with A. pallasii until Schmalfuss separated the two in 2006 on its heavier tubercles, a differently shaped frontal shield and a narrower tail tip. The peraccae wants a drier tub than this one, which our Armadillidium peraccae care guide sets out.
What It Looks Like
Look at the face first. In the nasatum group, which this species belongs to, the frontal shield is drawn up into a plate that stands clear of the head. Here it is narrow, with rounded corners and a groove behind it, and once you have seen it you can pick the species out of a mixed tub at a glance. Behind it the back is granular, though the descriptions disagree on how strongly, and the tail piece is longer than wide with a broadly rounded tip.
The wild animal is grey. Brandt called it grey and unspotted, Stein in 1859 called it lead-grey, reading five faded museum specimens, and Schmalfuss gives grey to blackish grey with faint muscle spots. The animals in our own photographs of the wild-type line are a pale lilac-grey with a scatter of paler spots, the light end of that description rather than a different colour.
The Orange line is sold across the European hobby as a selectively bred form of Corfu-labelled stock; we could not find who first bred it or when, and no wild orange animal is on record that we could locate. The colour is a warm, semi-translucent orange with paler edges to each segment, which is why it looks lit from behind under a lamp, and the smallest animals in our photographs are cream rather than orange. Two UK sellers call the colour hypomelanism, a shortage of dark pigment. We do not: woodlouse body colour comes from ommochrome pigments rather than melanin (no melanin has been found in the woodlouse cuticle, and the albino A. vulgare turned out to be an animal that cannot make ommochromes), the one colour line that has been studied, a red A. vulgare, was a shift in that same pathway, and we found no work on this one.
Size is the species' claim to fame, and here the record is better than usual. Schmalfuss measured the largest animal in his material at 21.5 mm long and 9.5 mm wide, which is the published maximum and what our care panels carry; Budde-Lund's series in 1885 ran 16 to 18 mm, with the odd animal at 20. The trade quotes anything from 20 to 25 mm, and none of those figures cites a measurement. At 21.5 mm it edges the Clown's published 21 mm, so calling it one of the largest Armadillidium in the hobby is fair; calling it 24 mm is not. In 1859 Stein called it almost twice the size of the Sandstone, a comparison rather than a measurement, and our Sandstone isopod care guide has the other half of it.
One more animal needs separating from it, because the two share a colour and an island. The Armadillidium frontetriangulum 'Orange', which other sellers from the Netherlands to the United States call "Orange Corfu", is much the smaller at 15 mm, its orange carries white and yellow spots, and its forehead comes to a triangle rather than a shelf. If the orange is plain and the animal is big, it is pallasii.
Where It Comes From
Schmalfuss's 2011 range runs along the east coast of Italy, down the Dalmatian coast and its islands as far as Corfu, then round the Sea of Marmara and the Turkish and Bulgarian shores of the Black Sea, with Crimea carrying Brandt's question mark. Photographic records add the Karst and coast of Slovenia, the far south of Albania, Anapa on the Russian Black Sea coast and around twenty sightings across Crimea. Older records reach as far as Egypt and the Caucasus, but Schmalfuss says every record published since Brandt's needs re-examining, and we do not count them.
Corfu, then, is the southern end of the confirmed range, and a published locality: Budde-Lund listed the island in 1885 on another author's word, and Schmalfuss records two animals collected at Myrtiotissa on its west coast in 1982. Our own wild-type listing undersold that for a while and has been reworded. Our stock came to us labelled Corfu, as most of the European hobby's does; part of the trade labels its stock Croatian, and given the range either is plausible. We found no published identification of any hobby stock, ours included.
Almost nothing has been written about how it lives. What there is puts it in numbers under stones on the south coast of Crimea and in oak forest on the island of Pag, and the photographic records add the coast, karst country and towns, one of them inside Corfu's New Fortress. We found no published record of it in a cave, and it is absent from the Croatian cave catalogue. We found no study of its reproduction, lifespan or brood size either, so everything in the next three sections is keepers' experience, ours included.
Setting Up
Our care panels give 18 to 26°C and 50 to 70 per cent humidity. Both are keepers' figures: across Europe the trade quotes everything from 15 to 30°C, we found no test of the limits, and the humidity figures run from 45 to 80 per cent. What the trade does agree on is the shape of the set-up, which is a Mediterranean one: most of the floor dry, one damp end, and enough ventilation that the surface never sits wet. A heated British room covers the temperature band for most of the year, though a summer hot spell will take a room past 26°C for a few days, and this species has never needed extra heat from us.
Build the humidity as a gradient rather than a reading: a damp patch over about a fifth of the floor, under sphagnum and litter, and the rest left to dry under bark. I keep my colonies in 11-litre tubs with two large vents on opposite sides so air moves through rather than hanging in the box, and the deeper substrate a tub that size allows stops the dry end drying out completely in a heatwave. A starter group can go in something smaller, so long as it still holds that gradient; our guide to how big a tub isopods need explains why the gradient, not the head count, sets the size.
Give them 5 to 8 cm of a nutritious base, flake soil with white-rotted hardwood and organic topsoil, never coir, which holds water and feeds nothing. Cover it with dry hardwood leaf litter and lay cork bark and a flat stone or two on top, because an animal recorded in numbers under stones will spend its days under yours. They are calm, sociable and mostly nocturnal, so expect them at dusk and under the bark by day.
Feeding
Leaf litter is the staple, oak and beech for choice, and it doubles as shelter, so keep it deep and top it up before it runs low. Add rotted hardwood for the colony to work through and vegetables now and then. Two other suppliers say this species does better with a small, regular protein source than most Armadillidium, and we find the same; we know of no test of the idea, but we offer ours protein a little more often than our smaller species get it, a pinch of fish flake or a dried insect, and a dead cricket goes quickly. Our piece on feeding isopods dead crickets covers how much and how often. Calcium stays in the tub at all times, as cuttlebone or crushed limestone: an animal this size puts a great deal into each moult, and a colony short of calcium moults badly.
Breeding
Once a colony has settled it breeds through the year in a warm room. The settling is the part to be patient about. New groups can take a couple of months to get going, and the Orange line loses a few more animals than the wild type in its first weeks; we have seen both ourselves, and one other supplier reports the same. Start with a group of twenty or more rather than the bare minimum, which is how I start every colony here, and resist the urge to keep checking on them. If a colony outruns the space you have, our guide to regulating isopod breeding explains how to slow it down without harming the animals.
Frequently Asked Questions
How big do Armadillidium pallasii get?
The published maximum is 21.5 mm, measured by Schmalfuss in 2011; most adults in Budde-Lund's 1885 series were 16 to 18 mm. The 24 mm on some shop pages has no measurement behind it. Measure body only, from the front of the head to the back of the last segment, leaving out antennae and uropods, as our care panels do.
Are Armadillidium pallasii easy to keep?
Yes, once settled. The wild type is rated easy on our care panel. We rate the Orange line medium for its first few weeks only, because it loses a few more animals while it settles; after that the two are kept the same way.
How long do Armadillidium pallasii live?
We found no lifespan figure for this species from any keeper or publication. Other large Armadillidium are reported by keepers at two to three years.
Is Armadillidium frontirostre the same as Armadillidium pallasii?
Yes. A. frontirostre is an 1885 name for the same animal, sunk as a synonym in 2011. Stock sold in the UK as the Rhino Horned Roller under that name is this species by name, though we cannot say what is in anyone else's tub.
Do Armadillidium pallasii roll into a ball?
Yes. Ours close into a full, sealed ball when disturbed, and on an animal this size the ball is a big one.
Can Armadillidium pallasii live with other isopods?
Keep it in its own tub, though not for fear of hybrids. Different isopod species very rarely cross: we know of no documented cross between two genera, the woodlouse hybrids we have found in the scientific literature are all between subspecies of one species, and the best-known hobby report of a cross between species has not been confirmed genetically. The bigger risk in a shared tub is that one species crowds out the other.
Where to Start
A big, calm, easily recognised pill woodlouse with a better paper trail than most of the hobby's species. Our Armadillidium pallasii 'Orange' isopods are captive-bred here and carry the care panel figures above, and our Armadillidium care guide covers the rest of the genus.
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