Some isopods are built to roll. Porcellio spatulatus is built to lie flat. The body is broad and low, wide for its length, and it presses itself against bark and stone like a lid. That shape gave the species its name, and the older name it once carried, latissimus, simply means the broadest. The Coros line is a slate to powder-blue animal with a darker band down the back and a pale, almost glassy skirt around the edge. Ours are captive-bred here in the UK, and the current stock is on the Porcellio spatulatus 'Coros' listing.
Names, and Where Coros Is
The species is Porcellio spatulatus Costa, 1882, in the family Porcellionidae, the same family as the Dairy Cow and the common rough woodlouse. The World List of isopod crustaceans accepts it under that name and treats two other names as synonyms of it: Porcellio latissimus, Budde-Lund's name from 1879, and Porcellio nobilii, Tua's from 1900. Its distribution in the same list is four places: Sardinia, Corsica, Sicily and Tunisia. It is not a Spanish species, which is worth saying because its care is close to the Spanish giants' and the label gets borrowed. The big Spanish Porcellio are different species with their own care guide; this is a western Mediterranean animal.
Coros is a place rather than a colour. It is a historic district in the north-west of Sardinia, in the Logudoro a few kilometres from Sassari, around the towns of Ittiri, Uri and Usini, where the landscape is old olive groves and vineyards. A locale name like this means the line traces back to one population from one area rather than being bred up in a tub for a colour, and that is the appeal. Other Sardinian localities of the species exist in the hobby, and Coros has the reputation of being the brightest of them; it is the one we keep.
What They Look Like
The shape is the thing to fix in your mind. An adult is a broad oval, flat on top and low to the ground, with the side plates flared out into a wide rim. The ground colour is a slate grey that shades to powder blue, with a darker stripe down the centre of the back, fine pale speckling across the plates, and that pale rim which looks almost translucent at the edges. The eyes are black, the antennae long, and the uropods at the back show as two short points. Juveniles come out pale, cream to a washed-out grey, and darken towards the blue as they grow.
Size is 15 to 20 mm at adult, the figure on our care panel, and the hobby's sheets say much the same, up to 20 mm; no published adult measurement seems to exist. That puts it in the middle of the genus: bigger than a scaber, smaller than the Spanish giants, and because it is so broad it looks larger than the length suggests. Like every Porcellio it cannot conglobate. Instead of rolling it has two answers to being disturbed: it wedges its flat body under whatever it is sitting beneath, and if that fails it runs, with a turn of speed that surprises people used to pill woodlice.
Temperature: A Warm Room, and a Cable for a Cold One
Our panel gives 20 to 26°C as the ideal band, and that is where a colony grows and breeds at its best. An English home over the heating season averages around 19°C, which is just under the bottom of that band, so a colony on a shelf in a living room will slow through winter rather than stop, and pick up again as the room warms in spring. In a cold room, an unheated spare bedroom or a garage, they will stall, and the fix is the one I use on my own racking: a heat cable on a thermostat run along the back of the shelf, so the back of the tub sits a few degrees warmer than the front and the animals choose. Our heating guide covers the options and the mistakes. In a heatwave the danger runs the other way. Keep sustained temperatures under about 28°C: a tub in a sunlit window will cook, and our hot-weather guide says what to do on those few days a year.
Humidity: The Drier End of the Genus
This is the part that decides whether you keep Coros or lose them. The panel says 45 to 55%, a dry-country figure for a dry-country animal. The setup that works is a gradient with the bulk of the enclosure dry: keep roughly four fifths of the floor dry to the touch and one corner damp over a handful of sphagnum moss, watered when the moss dries out and not before. The animals use the damp corner when they need it and spend the rest of their time on the dry ground. A wet, sealed tub is how this species is lost.
Ventilation does the other half of the job. A tub for Coros wants air moving through it, not just a few holes in the lid. I fit two to four of our screw-in vents per tub, and the racking has oscillating fans that run through cycles of different speeds, which keeps the air moving without drying the damp corner out. Put the vents on opposite sides so the air has a path through. If the lid ever fogs, there is not enough airflow. The trade-off between ventilation and moisture is in our ventilation and humidity guide, and if fuzzy patches appear on the food or the damp corner, our mould guide explains which ones matter.
Substrate, Cover and Calcium
They are surface animals, not burrowers, so the substrate can be shallow: a few centimetres of flake soil is the base, because they eat what they live on and flake soil is food as well as ground; coir is ground and nothing more. Over it goes a layer of leaf litter, which is the everyday grazing, and a piece or two of rotten white wood. The substrate guide has the mix in full.
What matters more than depth is what sits on top. A flat isopod wants flat cover with tight gaps: bark flats stacked in layers, a piece of slate, cork with a narrow space beneath it. Give them a stack and you will see far more of the colony than with one lump of cork in the corner. I keep mine in 11-litre tubs, which hold a moisture and heat gradient better than a small box; our tub size guide goes through the options.
Calcium stays in the tub permanently. A broad animal has a lot of shell to rebuild at every moult, and a colony that runs short shows it as failed moults. A dish of crushed oyster shell or a lump of limestone in the dry zone covers it; our calcium guide explains why, and the moulting guide shows what a good moult looks like.
Feeding
Leaf litter and rotten wood are the background diet and they should always be there. On top of that, Coros are protein-hungry, like the Spanish giants: a protein feed two or three times a week. I use a pinch of dried shrimp, a few dried calciworms or a sprinkle of fish flake, rotated so the diet varies, because a varied diet boosts breeding. Protein shortage is the usual reason a Porcellio colony starts eating its own moulting animals: a moulting animal is soft and defenceless, and a hungry colony will not leave it alone. Vegetables in small amounts round things out, put in the dry zone and taken out before they mould. Our feeding guide and the piece on feeding insects cover the wider menu.
Breeding: Seasonal, and Willing
The Coros line has a reputation among keepers as a prolific breeder once it is established. A settled group in a warm, dry, well-fed tub produces broods through the warmer half of the year and slows in winter. The first weeks after arrival are slow: the animals need time to find the damp corner, the cover and the food, and a colony that seems to do nothing for the first few weeks is settling, not failing, provided the floor is dry and the lid is clear.
Sexing follows the genus: males carry longer uropods, the paired points at the rear, and our sexing guide covers it. Start with enough animals for a real mix of sexes. I start my own colonies at twenty or more, and the listing offers groups of five, ten and twenty; the colony size guide explains the maths. Mancae are tiny and pale and live in the leaf litter for their first weeks, so do not clean the litter out. If a settled colony has not produced anything by the end of a summer, the usual causes are in our breeding troubleshooting guide: too wet, too cold, or too little protein.
Who This Species Suits
Not a first isopod, and only because of the dry setup. Everything else about Coros is forgiving: it is hardy, it eats well, it breeds, and it tolerates a normal room. What it will not tolerate is a damp, sealed tub, and the moisture gradient takes a little confidence to run. If you are new to the genus, the scaber mix is the place to learn the basics, and our guide to the types of Porcellio lays the genus out. Once a dry gradient is second nature, Coros is the natural next step, and after it the Spanish giants. The rest of the Porcellio collection shows where it sits among its relatives.
Frequently Asked Questions
Where is Coros?
A historic district in north-west Sardinia, a few kilometres from Sassari, around the towns of Ittiri, Uri and Usini. The line is named for the locality its founding population came from. Our animals are captive-bred in the UK.
Is Porcellio spatulatus a Spanish isopod?
No. The World List of isopod crustaceans records it from Sardinia, Corsica, Sicily and Tunisia. The care is close to the Spanish giants', but it is a western Mediterranean species, not an Iberian one.
How big do Coros isopods get?
15 to 20 mm at adult, and broad for their length: spatulatus means spatula-shaped, and the old synonym latissimus means the broadest. No published measurement seems to exist; the figure is the hobby's and ours.
Do they need heating?
Not in a normally heated room. The band is 20 to 26°C and an English home over the heating season averages around 19°C, so a living-room colony slows in winter and picks up in spring. In a cold room, a heat cable on a thermostat along the back of the shelf is the fix.
What humidity do they need?
45 to 55%, which means a mostly dry enclosure: about four fifths of the floor dry, one corner damp over sphagnum, and enough ventilation that the lid never fogs.
Can Coros isopods roll into a ball?
No. No Porcellio can. They flatten themselves under cover instead and run if they have to, and they are quick.
Are they good for a bioactive enclosure?
Only a dry one. A rainforest vivarium is far too humid for this species and it will not last there. It does best as a colony in its own tub, where the gradient is under your control.
Every animal is captive-bred here, and every order is boxed double-walled around a ventilated tub of damp sphagnum and posted Monday to Thursday by tracked next-day Royal Mail within Great Britain, with a live-arrival guarantee and a 20% overcount included as standard.
Leave a comment