Trichorhina tomentosa, or as they are better known by their common name “dwarf white isopods”, are a variety of isopods massively popular in the reptile hobby for their use as cleaners and feeders. We even wrote an article about them and their benefits! So why would there be an article about dangers revolving around them?
Dwarf whites are an excellent cleaning crew for a variety of reasons; they don’t exhibit aggression, they don’t pose a risk to soft skinned animals (even without proper diet), and they are a small, chubby feeder that micro geckos and frogs can eat. Dwarf whites are one of few isopods that keepers can comfortably use in any sort of bio without fear of the isopods swarming and overwhelming their animals. They’re the go-to cleaner especially for sensitive species like amphibians and delicate reptiles.
The most evident issue lies in their proclivity for reproduction: although they are docile, dwarf whites breed to startlingly high populations in a short period of time. Dwarf whites are an all female species that reproduce through a process called parthenogenesis, due to this, a single individual can produce a brood monthly and infest a setup. While this doesn’t bother vertebrates (they are typically too large to notice them, and if they do, they eat them), it is a situation that becomes very stressful for smaller animals that live in the same level, such as other species of isopods. While the dwarves don’t directly attack the other isopods, the presence of a large population of tiny sentient rice is stressful for the larger species of isopods, specifically the females. Females become so stressed they may abort their broods or eggs prematurely, and this may cause female death. Both males and females may become so stressed that this inhibits breeding entirely.
If a brood is released from the brood pouch prematurely, they have a drastically lower survival rate. For species that protect and guide their young the first few weeks of life, this has even more of a drastic effect because the females may abandon their broods, lowering the survival rate even more. The combined effect of weak, stressed females, females dying from premature birth, and females not receptive to breeding at all causes a population to deteriorate very quickly.
The range of animals that dwarf whites affect is further expanded to other burrowing invertebrates as well. We’ve noticed that roaches in the Therea and Gyna genera specifically having issues with dwarf whites setting up shop. These roach species release their ootheca, or egg sac, and leave the baby roaches to hatch in the substrate externally. The exposure of the egg sac to the dwarf whites leaves an opportunity for it to be eaten by them. Roaches have a similar issue of being stressed by a large population of dwarf whites, and the female roaches may abort their ootheca prematurely. In many species of roach, this may be a death sentence that causes prolapse. Millipede keepers have had issues with dwarf white in cultures as well- millipede eggs are susceptible to being eaten by a large population of dwarf whites and the dwarves may stress out the millipedes. Roaches that utilize vertical areas, such as egg crates, and whose eggs hatch internally (this is called oviviparous, and is the same process that isopods reproduce), such as hissing cockroaches and dubia, can safely cohabitate with dwarf white isopods. Since they have a vertical space to escape the dwarves, and their eggs are not exposed, they are not as prone to stressing from a close environment with a large population of dwarf white isopods.
Dwarf whites are also a problem with millipedes. Millipedes lay and disperse their eggs throughout the setup, and although the isopods don't stress out the millipedes themselves, they will eat the eggs. We also recommend staying away from dwarf whites in other ground dwelling, egg laying invertebrates such as tarantulas. For invertebrates in a more arboreal setup (mantids, for example), or if the goal isn't breeding the animals, it is perfectly safe to use them as cleaners. Another animal that dwarf whites are a safe cleaner for is snails, however please keep in mind they may also eat snail eggs if given the opportunity.
If dwarf whites are noticed in an invertebrate setup, we recommend quarantining the setup completely. Remove as many of the visible desired isopods by hand from the setup, and then carefully sift through them again to ensure dwarf whites have not accompanied them along on their journey. We recommend using a paintbrush for this task to move the isopods one by one. Place the desired isopods in a fresh setup, with new substrate and leaves, and do not take any décor from the previous setup. If it is preferred to keep a piece of décor (such as bark) bake at 200F for 2 hours to kill any dwarf whites that may be hiding inside. We recommend keeping the culture contaminated with dwarf whites and weekly harvesting the isopods as they grow to maintain as much of them as possible. Eventually, the culture will be only dwarf whites – at this point they can be labeled as such, or disposed of by freezing for 72 hours or baking/microwaving the substrate to sterilize it.