Isopods are surprisingly unfussy eaters, but a handful of foods can sicken or kill them. The short list of things to avoid includes aromatic woods like cedar and pine, plants from the onion and garlic family, copper-contaminated materials, and certain fruit tree leaves. Knowing what to keep out of your enclosure matters just as much as knowing what to put in.
Cedar, Pine, and Other Toxic Woods
Cedar and pine are the two biggest offenders. Both contain volatile organic compounds (VOCs), aromatic chemicals that irritate skin and respiratory membranes in small animals. In an enclosed isopod habitat, these compounds build up quickly because there’s no natural ventilation to disperse them. Research on laboratory animals housed on pine and cedar shavings found enlarged livers, impaired immune function, and decreased reproduction over time. Rats and mice actively avoid these shavings when given a choice, and isopods show a similar aversion to pine needles in feeding studies, consuming far less of them and absorbing fewer nutrients compared to preferred leaf litter like oak or alder.
Beyond pine and cedar, several exotic hardwoods are also unsafe. Cocobolo, ebony, purpleheart, rosewood, padauk, sassafras, and greenheart all contain compounds that can harm invertebrates in an enclosed space. Black walnut is particularly worth remembering because it’s common in North American yards. Its wood and leaves both produce a chemical called juglone that is toxic to many organisms. If you’re collecting bark or wood from outdoors, stick to hardwoods like oak, maple, or birch that don’t carry these risks.
Leaves That Can Harm Your Colony
Leaf litter is a staple of the isopod diet, but not all leaves are safe. Avoid leaves from cherry, chokecherry, birdcherry, peach, and apricot trees. These members of the Prunus family contain compounds that can release cyanide when chewed and digested. Since isopods are cleanup crew animals that munch directly on decaying leaves, this is a real concern rather than a theoretical one.
Pine needles and cedar leaves should also stay out of the enclosure for the same VOC reasons discussed above. Eucalyptus leaves are another poor choice. In feeding studies, isopods showed very low consumption of eucalyptus, along with poor assimilation ratios and low assimilation efficiency, meaning the animals couldn’t extract useful nutrition from them even when they did eat. The essential oils in eucalyptus likely act as a deterrent and a digestive irritant. Oak and alder leaves, by contrast, are consistently among the most preferred and nutritious options for terrestrial isopods.
Onions, Garlic, and the Allium Family
Onions, garlic, leeks, shallots, and chives all belong to the Allium family, and all contain sulfur-based compounds that are broadly toxic to small animals. The primary culprits are sulfoxides and aliphatic sulfides, chemicals that damage red blood cells by interfering with an enzyme needed to protect them from oxidative stress. The principal toxin, n-propyl disulphide, is present in all Allium species. While most toxicity research focuses on dogs and cats, isopods are far smaller and more vulnerable to these same compounds. There’s no reason to offer Allium scraps, and many keepers report their colonies simply refuse them anyway.
Copper-Rich Foods and Materials
Copper has an unusual relationship with isopods. As crustaceans, they need copper for their blood (it’s part of haemocyanin, the protein that carries oxygen in their bodies). But unlike aquatic crustaceans, land isopods get nearly all their copper from food, which makes dietary copper levels critically important. In uncontaminated leaf litter, copper sits around 5 milligrams per kilogram of dry weight. Concentrations above 1,000 milligrams per kilogram significantly increase mortality.
In practice, this means you should avoid feeding leaves collected near roadsides, industrial sites, or areas where copper-based fungicides have been sprayed. Isopods can detect copper-contaminated food and will try to avoid it when given a choice, but this self-regulation only works to a limited degree. In studies where isopods had access to both contaminated and clean food, their body copper levels still rose over time. When only contaminated food was available, mortality climbed sharply with longer exposure. If you collect leaf litter from the wild, source it from clean woodlands away from traffic and agriculture.
Pesticide-Treated and Chemically Contaminated Foods
Any produce or plant material treated with pesticides is dangerous for isopods. Organophosphate insecticides like dimethoate inhibit a key enzyme in the isopod nervous system (the same class of chemicals used in many garden pest sprays). Research shows that contaminated food decreases isopod performance across multiple measures: less consumption, lower assimilation, and increased oxidative stress in their tissues. Temperature makes this worse, since warmer enclosure conditions amplify the toxic effects of chemical contamination.
If you feed vegetable scraps, use organic produce or wash conventional produce thoroughly. Avoid anything from lawns or gardens that have been treated with herbicides, fungicides, or insecticides. Even “pet-safe” lawn treatments can contain chemicals that are harmful to invertebrates.
Citrus, Salt, and Processed Foods
Citrus fruits are widely avoided by experienced isopod keepers. The high acidity and essential oils (particularly limonene) in oranges, lemons, limes, and grapefruit can irritate isopods and disrupt the pH of the substrate. Small amounts of citrus peel probably won’t wipe out a colony, but there’s no nutritional reason to offer it when safer options exist.
Salty, spicy, or heavily processed foods have no place in an isopod enclosure. Isopods breathe through gill-like structures that must stay moist, and salt draws moisture out of tissues. Processed foods also introduce preservatives, artificial flavors, and oils that isopods have no biological ability to handle. Stick to plain, unprocessed plant matter: decaying hardwood leaves, vegetable scraps (zucchini, carrot, squash, cucumber), and calcium-rich supplements like cuttlebone or eggshell.
Quick Reference: Foods to Avoid
- Woods: Cedar, pine, black walnut, sassafras, rosewood, cocobolo, ebony, purpleheart, padauk, greenheart
- Leaves: Pine needles, cedar, eucalyptus, cherry, chokecherry, peach, apricot, black walnut
- Alliums: Onion, garlic, leeks, shallots, chives
- Produce: Citrus fruits, anything treated with pesticides or herbicides
- Other: Salty or processed foods, anything collected near roads or industrial areas, copper-contaminated materials
The safest approach is to mimic what isopods eat in nature: decaying hardwood leaves, rotting wood from safe species, and the occasional vegetable scrap. When in doubt about a food source, skip it. Isopods thrive on simplicity, and a clean diet of oak leaves, calcium supplements, and the occasional bit of squash will keep a colony healthy for years.