Cubaris sp. 'Black Pearl' Isopods

Some isopods win you over with pattern; the Cubaris sp. 'Black Pearl' works the other way. It stays dark and understated until the light hits it, when a soft, pearl-like sheen rises across the shell and gives the morph its name. That lustre over a deep, near-black body is the whole appeal for me, elegant rather than flashy, the sort of isopod that rewards a slow look under a torch.

Adults reach around 15 mm, which is small to medium for the genus, and the colour holds from birth, so juveniles arrive dark and simply deepen as they grow. An individual can look a shade paler for a day or two after a moult, which is normal while the new exoskeleton hardens. The sheen is what sets Black Pearl apart from its dark relatives: not the hard, cut-gem sparkle of the faceted Black Diamond, nor the flat solid black of a Black Sapphire, but a softer, lower-key lustre. Like the rest of the genus, these come from humid, limestone-rich cave country in Southeast Asia, most likely Thailand or Vietnam, and that background shapes their care.

I keep mine warm, in the 20 to 26°C band that suits most tropical Cubaris, and steadiness matters more than the exact figure, so I avoid windows and radiators. Humidity sits around 70 to 80%, arranged as a gradient rather than kept even: a damp side with sphagnum moss that I mist, and a drier side that still carries leaf litter. Cross-ventilation on a low-to-medium setting keeps the air fresh without drying the box out. Substrate is where this care is won or lost. I use a moisture-retentive, calcium-rich mix of pesticide-free topsoil, sphagnum and flake soil with crushed limestone worked through, at least 5 to 8 cm deep so they can burrow. I avoid coco coir as the main ingredient, since it holds little calcium and turns acidic. A constant calcium source, be it limestone, cuttlebone or powdered eggshell, keeps moults clean. When startled they conglobate into a tight ball, and a dark, faintly glossy sphere is a lovely thing to find.

Feeding is undemanding. As detritivores they graze on decaying hardwood leaf litter, with oak, beech and hawthorn all working well, plus soft white-rotted wood. Everything else is a supplement: a little carrot, courgette or squash cleared within a day or two, the odd scrap of fruit, and a pinch of protein such as fish flake or dried shrimp once or twice a week. I feed fresh food sparingly, since leftovers invite mould in the humid conditions the colony needs, and a springtail culture alongside them clears most of it. They are shy, nocturnal and happiest hidden, so cork bark, leaf litter and moss help them feel secure. If you want isopods forever on show this is not the species, but a night-time sighting of that sheen is worth the wait.

Breeding is steady rather than explosive. Females carry their young in a brood pouch and release them fully formed, broods tend to be small, and a starting group of six to ten gives a colony the best chance to settle. Stable warmth and humidity do most of the work, so the kindest thing is to resist digging to check on them. Black Pearl sits among the premium dark Cubaris, and if you are weighing it against the rest of the Cubaris collection, pick it for soft lustre over a dark body rather than bold pattern. Whichever you choose, colonies leave us double-boxed with a live-arrival guarantee, dispatched from the UK.

Common questions

Are Black Pearl isopods good for beginners? I would treat them as a step up. They are not the hardest cave Cubaris, but they reward some experience with humid, stable setups, so a hardier species first is sensible.

How big do they get? Adults reach roughly 15 mm.

Do they keep their colour as they grow? Yes. Juveniles are born dark and hold it, though an individual can look slightly paler for a day or so right after a moult.