Isopods are crustaceans. That trips people up right away because they look like bugs, live in the soil, and curl up when you poke them. But they are more closely related to crabs and shrimp than to any insect. They breathe through gill-like pleopods on their underside, which is why humidity matters so much in captivity. Let them dry out and they suffocate. It really is that simple and that unforgiving.
The enclosure
A plastic tub with a clip-on lid works perfectly. Really Useful Boxes are popular in the UK hobby for good reason: they are cheap, stack well, and seal enough to hold humidity. Drill or melt small ventilation holes in the lid or upper sides. You want some airflow, but not so much that the substrate dries out within a day.
Size depends on colony size. A 9-litre tub suits a starter culture of 10-15 isopods. As the colony grows, move up to a 33-litre or larger. There is no such thing as too big, only too empty. A huge tub with five isopods in it makes food hard to find and monitoring difficult.
Substrate
This is where most of the work goes. A decent mix is roughly 60% coco coir or organic topsoil, 20% sphagnum moss, 10% fine sand, and 10% leaf litter mixed through. On top of that, add a thick layer of dried oak or beech leaves. The leaves are food as much as they are cover. Avoid anything from conifers: pine and cedar contain phenols that are toxic to isopods.
Depth should be 5-8cm at least. The isopods need to burrow, and gravid females will retreat into the substrate to brood. A thin layer of substrate gives them nowhere to go.
The moisture gradient
This is probably the single most useful concept in isopod keeping. One end of the tub should be damp. The other end should be drier. Mist the damp end regularly, and leave the dry end alone. The isopods then move between the two as they need to. A uniformly soaked enclosure is just as dangerous as a uniformly dry one. Waterlogging drowns mancae (the baby isopods) and promotes bacterial growth.
Temperature
Most commonly kept species do well at normal UK room temperature: 18-24C. Tropical species like Cubaris need it warmer, around 22-26C, and may need a heat mat on a thermostat during winter. Never place the enclosure in direct sunlight. Even a windowsill on a warm day can cook the contents of a plastic tub surprisingly fast.
Calcium
Non-negotiable. Isopods need calcium to mineralise their exoskeleton after every moult. Without it, they produce soft, malformed exoskeletons and die. A piece of cuttlefish bone in the enclosure at all times is the easiest approach. Crushed eggshell or limestone also works. Just make sure there is always some available.
Feeding
The leaf litter and decaying wood in the enclosure form the bulk of their diet. On top of that, offer vegetable scraps once or twice a week: cucumber, courgette, sweet potato, and carrot all go down well. Protein once a week, sparingly. A small pinch of dried shrimp or fish flakes is plenty. Overfeeding protein is the fastest route to a grain mite infestation.
Remove uneaten fresh food within 48 hours. Rotting veg in a warm, humid enclosure turns into a mould factory very quickly.
Ventilation and mould
Mould panics new keepers more than almost anything else. White mould on decaying wood and leaves is normal. It is part of the decomposition process and the isopods will often eat it. Green or black mould is a sign that ventilation is poor and the substrate is too wet. Increase airflow, reduce misting, and let the damp side dry out a bit. A few more ventilation holes usually sorts it.
Springtails
Adding a culture of springtails (Collembola) to your isopod enclosure is well worth doing. Springtails are tiny arthropods that eat mould and fungal spores. They handle the stuff too small for isopods to bother with. Together, the two form a solid cleanup crew. You can buy springtail cultures cheaply, and once added they tend to establish and maintain themselves.
Handling
Most isopods tolerate gentle handling. Scoop them up rather than pinching. Armadillidium species will roll into a ball, which makes them easy to pick up. Porcellio species tend to run, which makes them slightly less cooperative. Wash your hands before and after. Lotions, insect repellent, and cleaning product residue on your fingers can harm them.
What can go wrong
The colony crashes silently. That is the frustrating thing about isopods. They don't make noise or act obviously sick. You just open the lid one day and the numbers are down. Common causes:
- Desiccation from insufficient humidity or too much ventilation
- Waterlogging from too much misting and not enough drainage
- Calcium deficiency leading to failed moults
- Mite explosions from overfeeding protein
- Toxic substrate materials (conifer-based products, pesticide-contaminated soil)
Most of these are fixable if you catch them. The problem is that "catching them" requires actually checking on the colony regularly. Lift the bark, look under the leaf litter, and count roughly how many you can see. If numbers drop, work through the list above.
Where to start
Porcellio scaber and Armadillidium vulgare are the classic starter species for good reason. They tolerate a wide range of conditions, breed readily, and come in some nice colour morphs. Get a culture of 10-15, set up the enclosure properly, and leave them largely alone for the first month. Resist the urge to dig through the substrate every day. They will sort themselves out.