Isopod Substrates & Enclosures

Terrestrial isopods are increasingly popular pet invertebrates, and I imagine this has much to do with how simple they are to keep in captivity. Most of the species in the hobby thrive on similar diets and in nearly identical enclosures. Accordingly, the environments I provide for my isopods are broadly similar to most isopod keepers' setups, although I've made a few changes to the basic isopod tub that make maintenance easier and mimic natural habitats. As a disclaimer, I'll mention here that some of the materials I use might be difficult to replicate since I gather them myself, but I hope that this writeup gives you some helpful tips even though I don't think you need to recreate it identically. It works well for me though, so I’d like to share it! Suggestions, critiques, and questions are all welcome.

Porcellio scaber morph mix

The tubs and cups I keep my isopods are old plastic bins once used for storage or were leftover from other invertebrate projects. My isopod enclosure style should work in most containers though, but due to the thickness of the substrate a taller container might work better than a shallow one. I tend to add a lot of cross-ventilation to my enclosures since I stack them on top of one another. 

I start with soil that is compressible and holds its shape well. Most isopod substrates I see used are either coir/cocofiber or peaty potting soil, and while I'm sure they work well for people who like them, neither of these compact well. What I use is a mixture of silty clay I dug up from the garden and strained until pure, plus varying amounts of topsoil, old potting soil, used centipede substrate, cocofiber, Pycnoscelus cockroach frass, sand, and other sundry substrates. It really doesn't matter what this compacted layer is made of, so long as it stays firm and doesn't shrink away from the sides too much. Topsoil for gardens probably works just as well as my bizarre dirt mix and a big bag of it won't require you to sit around sifting clay for a whole summer. Be careful of topsoil with fertilizers, and check for worms, centipedes, and other hitchhikers that might bother your isopods.

    

Next, I compress the substrate until it's too firm to dig and essentially forms a solid brick of dirt. Adding a layer of substrate, then misting with water helps make compression easier but be careful not to make the soil into mud, in which case it will need to dry a little longer after compression. I typically just use my hands to pack it down but an old spoon or other implement works too. It's a bit time-consuming, but the reason I love well-compacted substrate is that it's fairly permanent. As isopods defecate, their frass builds up in the upper, loose layer of substrate, while the lower compact layer acts as a floor and doesn’t become fouled. I often find that my substrate doesn't easily become hydrophobic, so it's less irritating to water than peat-based soil. A good compact layer also resists deep burrowing, which can be a nuisance when I'm trying to keep count of the inhabitants. All of these mean that the compact layer can be swept clean and reused, and only needs to be torn up, re-mixed, and compacted again if I want to refresh the entire culture.

The inspiration for the substrate is actually from the place I find wild isopods in large numbers in the garden: under slates and bark on top of hard clay soil, with little burrowing going on and slight frass buildup. I’m not sure if it’s still widely given as advice, but when I’d just started keeping isopods more than a few caresheets recommended a wholly edible wood-and-leaf substrate. Unlike millipedes, most isopods don’t need to burrow deeply and prefer dead leaves over wood in my experience, so there’s no need for a deep edible substrate, just one that can retain moisture and is a good texture to walk on. 

However, most isopod species do appreciate having some sort of loose material in which to make shallow burrows, so I typically add a layer of gritty material on top. The very smallest baby isopods can take refuge between the larger particles, and larger juveniles and adults can make hollows in it to rest or molt. Armadillidium tend to make good use of this layer, so I give them enough to bury themselves in. Other, non-conglobating species seem to benefit from this layer keeping the bark pieces elevated so they can fit under them, and also as texture to walk on. Most of my grit is hardened bits of clay, mulch or bark sifted out of topsoil, and a few pieces of gravel or calcareous chicken grit for variety. Cocofibe, coconut husk chunks, hardwood mulch, or non-coniferous bark fines for orchids would probably work very well here. The reason that I use larger grit particles is so that I can sweep out the entire loose layer, sift the smaller frass particles out, and then return the clean grit back to the enclosure. I let a moderate amount of frass build up, since it's a decent medium for baby isopods to burrow in, and they'll also eat it to gain their parents' gut flora.

Once the substrate is built, I'll lay in the bark pieces. I tend to use bark I find from local dead trees since it can be lighter and thinner than cork, but cork bark is a safe and reliably clean material that most breeders use since it comes in large pieces that fit large tubs. I'll probably do the same if I ever keep that kind of volume of isopods, although I don't like how heavy cork can get. Lighter bark can be stacked to maximize surface area for clinging, although not all species like to be that far from the soil. A good rule of thumb is that there should be plenty of room left over even when every isopod is clinging to bark; although the entire colony might choose to cluster together under one piece quite tightly, it's important to give individuals the option of having some space if they need it.

The final component of the enclosure is the dead leaves that will form the majority of the isopods' diet. Laying them on top of the bark can also help maximize surface area, and my isopods often climb to the leaf layer to molt away from the bustle of the colony in the bark layer. I find that they have a strong preference for soft, non-waxy, and very well-decayed leaves. I mainly use maple, since that's what's most common locally, but very old cottonwood litter is another favorite of theirs. Isopods will eat most any kind of dead leaf if they have to, but magnolia and very glossy oaks don't seem to be well-received. I soak my leaf litter in water for a few days to leach out the tannins, and dry it for storage—not a required step, but it keeps the leaves clean and makes them more edible.

Maintenance on enclosures of this style is mainly piling more leaf litter on as it gets eaten and adding water to the substrate as it evaporates. The loose layer needs to be sifted every month or two, but more frequently for a dense population and less for a small one. I use a cheap mesh strainer for kitchen use to sift the substrate. The frass that falls through might include baby isopods, so I sift into a container and pluck them out. Putting the entire old frass layer into another tub and letting the baby isopods grow to a more visible size also works. I also keep springtails with all of my cultures since they don't appear to bother isopods at normal population densities and work wonders on fighting mold. My substrates also tend to be inhabited by small oribatid mites, which serve the same function as the springtails, and larger predatory mites, which eat the springtails but also any grain/mold mites or fungus gnats that can be nuisance pests (I haven't seen a fungus gnat indoors for over 5 years).

For isopod populations of 2-20 adults, and especially when they're a new morph or otherwise part of an important breeding project, I'll house those few in 1/2 qt, 1/4 qt, or small condiment cups (I think mine are 5.5 oz). I build these exactly like the big tubs, with a compact layer, bark, and leaves to scale with the cup. The grit layer is optional at this size for clinger-type isopods but I recommend it for Armadillidium and other roller-types. The benefits of a small cup are that it's easy to find every individual, including newborns, and also to check food availability. Because crowding is more of a concern in these smaller enclosures, it's important to offer a lot of surface area by stacking bark and also to keep a close eye on the population.

These cups don't last very long. For example, a breeding pair of Porcellio scaber raised from small immatures (to maintain single-pair mating) in a 5.5 oz can be moved with their first clutch once the offspring are ~4 mm into a 1/4 qt cup, and then maybe into a 1/2 qt once they grow a bit more. A group of 10-15 small adults in a 1/2 qt should be moved with their started offspring into a tub before the offspring start getting too crowded. The entire run from pair to 50-strong colony can happen in under a year, so each size of cup might only see use for a few months.

Overall, I quite like my method of building isopod enclosures, though there are probably a few things I might need to improve for species that need to burrow deep (though I don't expect to keep Helleria or Hemilepistus anytime soon), burrow in sand (same for Porcellio spinipes, P. albinus), or need very moist substrate. Otherwise, the enclosures are easy to clean, waste little to no substrate beyond the discarded frass, and are easy to find locate individuals in. The downsides are that the tubs can get quite heavy due to the solid clay substrate, and when poorly maintained can dry so that gaps form between the walls and the compact layer, allowing baby isopods to get stuck or get lost under the entire substrate. 

Still, for the ~4 years I've been using this method, I've had great success with my collection, and as picky as I am about how I build them, these enclosures work well for my purposes. I plan to follow this up with a sheet on feeding isopods, and another on selective breeding for color morphs, both of which will probably be more applicable for general use!