The quickest way to find out whether an isopod colony is alive is to feed it. Drop a slice of zucchini on the litter, come back in a day or two, and look. Gone or half gone means a hungry, healthy colony. Untouched and growing mold means a small or struggling one. We use that bait test every week on tubs where we otherwise cannot see the animals at all, and it works because isopods are, above everything else, eaters. Here is what they eat, how much, how often, and the one feeding mistake that causes more crashed tubs than anything else.
The staple: leaf litter and rotting wood
Isopods are detritivores. Their everyday food is dead leaves and decaying wood, and the fungi and bacteria growing on both. Oak leaf litter is the standard because it breaks down slowly and stays palatable for weeks; magnolia and beech work too. White-rotted hardwood, wood that has gone soft and crumbly because fungus decayed it, is the other half of the staple diet and the part beginners skip. Dry brittle wood is not the same thing; it is a hide, not a meal. Both should be in the tub at all times, and when the litter layer is gone, the colony is telling you it is hungry. We top up litter whenever the surface starts showing soil.
This is also why substrate matters: a tub of pure coco coir has nothing growing in it to eat. The substrate mix we use is topsoil-based with rotted wood crumbled in, which means the tub itself is food.
The supplement: protein twice a week
Litter alone grows a slow colony. A small protein supplement grows a fast one and, in a tank with millipedes or a soft-bodied pet, it also keeps the isopods from looking for protein elsewhere. Armadillidium rollers like our zebras and Montenegros have a noticeably stronger protein drive than the dwarf species, so this matters more for them. Twice a week we put a pinch of fish flakes, dried shrimp, or dried worms on the dry side of the tub, and whatever is left after a day or two comes out. Discus flakes are what we happen to have; any plain fish food works. We tried the idea of brine shrimp and dropped it before it went in: aquatic food rots fast in a damp tub and adds nothing the flakes do not.
Calcium: cuttlebone, not eggshell
Every molt rebuilds the shell, and rollers carry a heavy one. A piece of cuttlebone, the kind sold for birds, sits in each of our tubs and gets rasped down over months. Crushed eggshell is the usual free substitute, and keepers generally rate it a weak one. We have only ever used cuttlebone, so that is a view we are passing on rather than anything we tested. One piece lasts most of a year. For Cubaris species like rubber duckies, keepers generally go further with limestone and calcium carbonate in the substrate, but for Armadillidium and Porcellio, cuttlebone is enough.
Vegetables: treats and bait, not the diet
Zucchini, squash, carrot, sweet potato, cucumber. Isopods love all of them, which is exactly why they are useful as bait for the health check and for harvesting, and why they are dangerous as a daily food. A slice of vegetable that sits uneaten for three days molds, and mold plus moisture plus uneaten food is how you get a mite bloom. Feed vegetables in an amount the colony finishes in a day or two, and pull anything left after that. A thin slice for a starter colony; a chunk for a booming tub.
How often to feed isopods
Litter and wood: always present, topped up as it disappears. Protein: a pinch twice a week, uneaten bits removed. Vegetables: a small piece once or twice a week, or whenever you want to check on them. Cuttlebone: one piece, replaced when it is gone. That is the entire schedule. A colony fed this way will show you a mix of sizes under the hide within a couple of months, which is the sign that it is breeding.
The mistake: overfeeding
More food does not mean a faster colony. It means moldy food, a sour tub, and a gray dusty film of grain mites on the surface within a week. Overfeeding is the number one killer of new tubs, ahead of drying out and ahead of too wet, and it is the easiest to fix: feed only what they finish quickly, and if you already have mites, cut the food, let the surface dry a little, and wait. The mites are a symptom of the buffet, not a plague. Springtails help here too, because they eat the mold before it feeds anything else; how to keep a culture of them is in springtail culture care.
What isopods eat in a bioactive tank
In a display tank with plants, the answer is the same food plus everything else that dies: shed skin, waste, dead plant matter, the occasional dead feeder insect. That is the cleanup-crew job. Keep the litter layer generous in a display tank, because a hungry colony with no litter will start on live plant leaves and on anything soft that is molting, including a millipede. The tank build that keeps the crew fed from day one is in how to make a bioactive terrarium. And if what you need is the litter itself, our heat-treated hardwood litter is in the shop.
Questions people ask
What do isopods eat? Dead leaves and rotting wood as the staple, a small protein supplement, and calcium from cuttlebone. Vegetables as an occasional treat.
How often should I feed isopods? Keep leaf litter and wood in the tub always. Add a protein pinch twice a week and a small vegetable piece once or twice a week, removing leftovers after a day or two.
Do isopods need protein? Yes, a little. Fish flakes, dried shrimp, or dried worms twice a week. Rollers like Armadillidium want it more than dwarf species.
Can isopods eat fruit? Small amounts, rarely. Fruit molds and ferments fast in a damp tub; vegetables are safer bait.
Why are there mites in my isopod bin? Almost always overfeeding. Cut the food, let the surface dry slightly, and the mites fade with the mold.