Mould in an Isopod Enclosure: What It Is and What to Do

Quick answer: the white fuzz on your wood is almost certainly saprotrophic fungus doing what fungus does to dead wood in a damp box, and no fungal disease has ever been recorded in any terrestrial isopod. What to do about it is usually nothing, or a small change to airflow and to how much fresh wood and food you are putting in. What not to do is dry the enclosure out.

The longer version is more interesting, because much of what the hobby repeats about mould has nothing behind it, including something we have printed ourselves.

What the white fuzz actually is

Nobody knows. That is the state of the evidence, not evasion: no published study has sampled the fungi growing in a hobby invertebrate enclosure.

What has been sampled is the fungus growing on the animals. A 2025 study used DNA metabarcoding on Armadillidium vulgare and found a community roughly two-thirds Ascomycota and one-third Basidiomycota, dominated by wood-rot and soil genera. The important finding was that habitat, not the animal, shaped the community. The fungi on a woodlouse are the fungi of the place it lives. And it took genetic sequencing to identify them, which tells you how much confidence to place in anybody who looks at a photograph of white fluff and names it.

So we will not tell you your fuzz is Mucor or Penicillium or anything else. We can tell you what it is doing: colonising dead wood, leaf litter or uneaten food, which is the normal first stage of decomposition (see rotten wood) and the reason those materials are in the enclosure at all.

Does mould kill isopods?

Not one documented case exists. We searched the medical and veterinary mycology literature for the two fungi that famously kill insects, Beauveria and Metarhizium, paired with isopods. Zero results for both. A broader search for fungal infection in woodlice returns a single paper, and in it the woodlice are a reservoir for a fungus that causes skin lesions in horses, not victims of it.

Meanwhile the things that genuinely are documented as isopod pathogens are bacterial, viral and parasitic: a Rhabdochlamydia that infects Porcellio, a rickettsial disease recorded in British woodlice, Wolbachia, parasitoid flies, and the nematode-plus-bacterium complexes sold as garden biocontrol. The isopod immunity literature challenges animals with bacteria and viruses. Nobody has published a fungal challenge study at all.

The honest position is therefore "no documented case", not "impossible". Fungal disease is well known in aquatic crustaceans; terrestrial isopods simply have not been studied as a host. But if mould were routinely killing colonies, somebody would have written it up by now.

The bit the hobby gets backwards

You will read everywhere that isopods eat mould and will clear it for you. They do graze fungus, and there is good work behind that: woodlice grazing wood-decay mycelium in the lab change which fungus wins a territorial contest, and Porcellio laevis grazing a white-rot fungus reduced its biomass in the grazed patch.

But two things complicate it. In that same P. laevis experiment the fungus compensated, growing more elsewhere in the dish instead of less overall. And a 2023 study states plainly that Porcellio scaber does not selectively graze fungi, with fungal abundance rising in the animals' presence.

Fungal identity also matters more than fungal presence. Given a choice of diseased pear leaves, Porcellionides pruinosus ate one fungus almost to nothing, largely ignored a rust, and survived worse when fed the rust.

So: isopods interact with fungi, sometimes heavily. They are not a mould-removal service, and buying more of them will not clear a bloom.

Springtails do not clear mould either

This one is stated as fact across the hobby and has never been tested. No study has ever measured whether adding springtails to an enclosure reduces visible mould.

What the soil literature does show is that springtails are selective fungivores, preferring fungi without chemical defences, and that the direction of the effect depends on how hard they graze. Low-intensity grazing frequently stimulates fungal growth. In one experiment that ranked invertebrate groups directly, the large animals did the most damage to mycelium while the small ones often stimulated it, which puts isopods ahead of springtails on this specific job. Grazed fungi can also fight back, increasing toxin production and fruiting.

Keep springtails because they are excellent at consuming waste and moulding food before it sours, and because they are a genuine early-warning system for a tub going wrong. Do not keep them as a mould treatment.

What actually kills a humid enclosure

Here is where we have to correct ourselves. We have printed, on nine of our own Ardentiella pages, that stagnant humid air is the fastest killer they face, and described it as the best-corroborated fact about the genus because nine independent sources said so. Going back through it carefully: those nine sources are nine shops. Nine vendors agreeing is one hobby belief repeated, not nine pieces of evidence. There is no study, no measurement and no case report behind it anywhere.

We still ventilate those species heavily, because the reasoning is sound and because it works on our shelves, particularly for the Ember Bee and its relatives. But it is house practice, not a fact, and we should have said so.

What is measured is more useful anyway:

They breathe out ammonia, and they cope with it

Woodlice release most of their nitrogen as gaseous ammonia straight through the body wall, not in their droppings; faecal ammonia is only about a tenth of the total, and output rises roughly fivefold in warm weather. That is a real mechanism and a good argument for airflow. But the one study that measured toxicity found P. scaber tolerating ambient ammonia to an extraordinary degree, with a seven-day LD50 around 880 parts per million, which is far above anything a vented tub is likely to reach. So the folk explanation that a sealed box poisons them with ammonia is not supported. Nobody has measured ammonia in a keeper's enclosure.

A moisture gradient only works if part of it is genuinely dry

This is the most actionable thing in this article and it comes from 1937. Testing P. scaber in humidity gradients, Gunn found the animals could detect a six per cent difference in relative humidity and would gather in the damp end reliably. But he also found no reaction at all when the whole gradient sat above 65 per cent.

In other words, a tub that runs 75 per cent at one end and 85 at the other does not give your animals a choice. It gives them one condition. If you want a working gradient, one end has to be genuinely dry, and that single change fixes more mould complaints than anything else we suggest.

Check whether your species even has lungs

Turn a live woodlouse on its back and look at the underside of the rear section with a hand lens. Pale white patches are pleopodal lungs. Trachelipus has five pairs and they are obvious. Porcellio, Porcellionides and Armadillidium have two. Oniscus asellus shows none, and neither do the small woodland species. It takes five minutes and it is a real diagnostic character.

What we will not do is tell you it predicts anything about tolerating still air. It is tempting, and the one study that tested metabolism against lung type found the relationship did not hold cleanly, with one lunged Porcellio behaving like a lungless species. Nobody has tested lungs against ventilation at all.

Mites, and the number worth knowing

A mould bloom and a mite bloom have the same cause, because the mites in question eat fungus. If white specks are moving, you have grain or mould mites, and the useful fact is that they are far more sensitive to humidity than your isopods are.

At 25°C and 70 per cent humidity, every larva of two of the commonest species died and neither reproduced. Population growth roughly doubles between 80 and 90 per cent. Bringing the dry end of a tub genuinely down is therefore a mite control as well as a mould control. There is no evidence that these mites harm isopods; the documented reason to care is that storage mites are a well-established human allergen. We have a fuller piece on mites and pests.

So what should you actually do?

Read the fuzz as information. A flush on fresh rotten wood or new leaf litter is normal, usually peaks in a fortnight, and settles as the culture matures. Persistent mould on uneaten food means you are feeding more than the colony can process. Mould creeping across the whole surface with no dry ground anywhere means .

The fixes, in the order we would try them: give the tub a genuinely dry end; add ventilation before you remove moisture, which on a Braplast box means vents, not a propped lid; feed less protein and take out whatever they leave behind (the feeding guide covers quantities); leave the wood alone. Do not sterilise, do not tear the setup down, and do not dry the whole thing out, which trades a cosmetic problem for a real one.

Common questions

Should we remove mouldy wood?

Not usually. The mycelium is decomposing the wood, which is why the wood is in there. Remove it only if the growth is slimy and foul-smelling rather than dry and fluffy, which suggests bacterial souring instead of fungal colonisation.

My isopods are sitting on the mould. Is that bad?

No, and it is the commonest thing people panic about. They are grazing microbially conditioned material, which is well documented as preferable to fresh litter.

Will more springtails fix it?

Probably not, on the evidence above.

Is white mould different from black mould?

Nobody has identified enclosure fungi by colour or otherwise, so anyone telling you what a colour means is guessing. Use texture and smell instead: dry and fluffy is ordinary, slimy and sour is a wet-substrate problem.

Can mould make me ill?

Take reasonable care. Storage mites are documented allergens and mould spores affect some people. Ventilate the room, keep your face out of the tub, and wash your hands.

How wet should the enclosure be?

Species-dependent, and we cover it in humidity for isopods. The universal part is the gradient: whatever your damp end reads, the dry end needs to be genuinely dry for the animals to be able to choose.

If a colony is going backwards rather than just looking untidy, our colony crash guide works through the causes that are actually documented. Setting up for the first time? Start with substrate and the beginner's guide.