Quick answer: Ardentiella, the group most keepers still call Merulanella, are Vietnamese isopods that need wet air and moving air together. Vent two facing walls through fine mesh, hold humidity somewhere in the 60s or very low 70s, as a slope rather than a fixed figure, and leave them at ordinary room temperature, anywhere from 19 to 26°C, with nothing added to warm them. They scale glass, they never dig, and warm still air is what empties a colony. Not one of them is a beginner animal, and when they fail it is nearly always the box at fault rather than the keeper.
This covers the group as a whole. If you have already settled on an animal, there are separate guides to Red Diablo, Ember Bee and Tri Colour, plus a rundown of how the morphs differ. What follows is what they all have in common.
Two names, one animal
Half the shops selling these say Merulanella and half say Ardentiella. Search both. You are looking at the same isopods whichever label turns up, and the change dates from March 2025, when Kästle and Regalado Fernández went back through museum material and concluded the old genus had been holding several unrelated things at once.
One detail is worth carrying, because it tells you how much weight a label deserves. The new genus was raised around two Myanmar species, and the Vietnamese animals that fill the pet trade were never part of that study at all. Everything now sold under the new name sits there on the hobby's reading rather than on anything published. No trade morph has a formal description, a type specimen or a recorded wild locality, which is why a careful listing gives you the genus, then a nickname in quotation marks, and stops.
The same paper raises something the trade rarely mentions. Parts of this group are regarded as threatened by collection for the pet market, even though none of them carries an IUCN listing. Wild-caught stock is also far harder to settle than captive-bred, so on this occasion the ethical answer and the practical one point the same way.
The problem that defines the genus
Everything difficult about these isopods traces back to a single demand. They want humid air that keeps moving, and those two things work against each other. Nearly anything that lifts humidity, whether you seal vents, deepen the substrate or mist harder, cuts airflow at the same moment. Get the balance wrong and the colony thins out quietly across a few weeks with nothing obvious to blame.
The answer is cross-ventilation rather than extra ventilation. Put fine mesh in one wall and more in the wall it faces, so air travels the width of the box instead of stalling. One vent, however generous, leaves dead volume behind it. This is the best-evidenced fact about the whole group, agreed on by every source that has anything to say about them, and one specialist supplier puts it flatly: without enough ventilation these animals do not survive.
With airflow sorted, aim for the 60s or very low 70s, damper at one end and drier at the far one so the animals choose for themselves. Published figures for this genus run anywhere from 60% to 90%, which should tell you to treat a single number as a starting point rather than a target. Keep the substrate damp throughout and never let it turn to swamp. Our humidity guide covers the mechanics.
Do not heat them
This is the correction I most want to make, because we gave the opposite advice ourselves until recently.
These are not cave Cubaris and a heat mat is the wrong instinct entirely. They tolerate 19 up to 26°C, sit happiest in the lower half of that, and start struggling past about 26. Sellers on two continents talk about summer heat killing colonies outright rather than merely slowing them down, and at least one specialist runs the entire genus at around 20°C by choice.
A British room manages this unaided. What threatens them here is a July heatwave, not a January night, so a steady spot out of the sun and clear of radiators is worth more than any equipment you could buy. Put a mat under one end of a small box and you dry the substrate out while building a hot corner that an animal which cannot burrow has no way to leave. If your house genuinely bakes in summer, sort that out first. There is broader context in our temperature guide.
They go up, never down
These are flat, quick, semi-arboreal animals. Sheer glass and polished plastic slow them not at all, the young manage it as well as the adults, and a manca will exploit a gap you cannot see. Go over the fastenings, the joins and the rim of every vent, and assume anything not sealed is an exit.
Since they spend their lives on wood rather than in soil, they get more use out of vertical space than floor area, and a tall box gets worked from bottom to lid. Set cork bark upright, give them branching routes off it, and far more of the colony stays in view than any flat hide will show you. Being Armadillidae they are built to roll, though it happens rarely enough that climbers is the better mental filing.
Substrate, litter and calcium
Build the floor from soil and sphagnum with rotted hardwood and leaf mould folded through. Coco coir alone will not serve, since it holds water without feeding anything living in it. Five to eight centimetres is ample for animals that spend their time above the surface, and what goes into the mix counts for far more than how deep you pile it. There is a working recipe in our substrate guide.
Bury that under a deep covering of hardwood litter, then add white rotten wood, which between them account for most of the diet. Something chalky stays in the box permanently: cuttlebone, oyster grit or limestone chips, whichever you can get. Rather than feeding to a timetable, replace the litter layer as it vanishes, offer a little soft vegetable, add protein from time to time, and remove any fresh food still sitting there a day later. At this humidity leftovers go mouldy fast.
Which one should you start with?
They are not equally difficult, and the differences are worth knowing before you spend.
Ember Bee is the usual door in. Sources with nothing to sell rate it the gentlest of the group, it happens to be the largest, and it is unusually willing to be out in daylight where you can watch it. That still does not make it a first isopod, but it leaves you more room for error than its relatives will.
After that, Red Diablo and Scarlet are the vivid reds, Phoenix is the parent form the yellow line was selected out of, and Tri Colour wears tidy bands of red, yellow and black. Everything above applies to all of them unchanged. The rest of the ones we stock are gathered in our Ardentiella range.
And if none of this sounds enjoyable yet, that is a fair conclusion to draw. Keep something tougher first, get comfortable with what ventilation actually does, then come back. Our beginner list is where to start.
Frequently asked questions
Is Merulanella the same as Ardentiella?
To a buyer, yes: both names sell you the same animals. Technically, no. The 2025 work left Merulanella covering three species from New Caledonia and set up Ardentiella around a pair of Myanmar species, with the hobby then shifting its Vietnamese morphs across on that reasoning. Both labels are still in circulation.
Do Ardentiella isopods need a heat mat?
They do not, and fitting one is a common way to lose them. A British room sits inside their range the whole year, and they favour the cooler half of it. In this country heat is the hazard and cold is not.
Why do Ardentiella colonies crash?
Stagnant humid air, nearly every time. Plenty of moisture with no cross-flow is how this genus is most often lost, and it works slowly enough that keepers usually blame the food or the animals. Vent two facing walls before you blame anything else.
Can Ardentiella isopods climb glass?
Yes, and so can the young. Your lid has to close tight everywhere apart from the vents themselves.
Are they good for beginners?
No. Even Ember Bee, the gentlest of them, gets rated intermediate to advanced by everyone who rates it at all. Come to this genus once you have kept something hardier alive for a while and understand what airflow is doing in an enclosure.
Are Ardentiella isopods captive-bred?
Ours are. Wild-collected animals in this group are considerably harder to establish and carry a real conservation question, given what the 2025 authors said about collection pressure. Worth asking any seller which you are being offered.
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