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!

House centipede caresheet

This caresheet is for Scutigera coleoptrata and Thereuonema tuberculata, two species of house centipede introduced to North America. Both species have similar needs, but other scutigeromorphs that are more adapted to desert or rainforest habitats may require different care and conditions.

Identification:

    With large compound eyes, hypersegmented legs, unpaired dorsal spiracles, and an unparalleled ability to make most people freak out, house centipedes are some of the most unique and recognizable myriapods. The two scutigeromorph species most common in the US are actually nonnative: Scutigera coleoptrata, introduced from the Mediterranean, and Thereuonema tuberculata, introduced from East Asia. I will refer to both together as “house centipedes” in this caresheet. Distinguishing the two can be difficult when comparing juvenile specimens, but while even adults can sometimes appear similar they are usually straightforward to identify using color and patterning. S. coleoptrata is generally a pale grayish yellow, with well-defined stripes on its tergites, while T. tuberculata can be quite dark brown in color with variably colored markings around its spiracles. Due to the two species' superficial similarities, the presence of T. tuberculata in the US was not detected until very recently although iNaturalist data shows that it is almost as widespread as the more familiar S. coleoptrata. Based on limited observations, T. tuberculata seems to prefer outdoor habitats, especially in warm weather. At the site where I collect mine, I often find T. tuberculata in small groups under stones although I have not experimented keeping this species communally yet.

Scutigera coleoptrata; Thereuonema tuberculata

Obtaining:

    Scutigeromorphs are not commonly kept, bred, or sold as pets, so you will need to catch your own if you wish to keep them. While quick and evasive, they can be captured with the cup-and-paper trick or chased into a cup or vial held flush with the ground. Avoid picking them up directly unless absolutely necessary (such as if someone else is trying to kill one) since a house centipede will likely autotomize many of its legs as an escape mechanism. House centipedes desiccate quickly in an empty container, so either have an enclosure on hand or be prepared to set up temporary containment that maintains humidity.

Enclosure & Conditions:

• Compact substrate: compacted soil or peat moss, can be mixed with clay/sand
• Climbing space: bark or corkboard at an angle with room to hang and molt
• Enclosure: should provide some height and some floor space
• Ventilation: drill or poke holes in the side for airflow.
• Temperaure: Roughly 60-75 F / 15-24 C. Tolerant of a range of temperatures.

    House centipedes are not very picky about substrate, but compacted soil seems to work better with their leg structure over fluffy and loose materials like coir/cocofiber (although coir can work in a pinch). Substrate depth is not greatly important since scutigeromorphs do not burrow, but the substrate should be deep enough to hold moisture. A diagonal or vertical, textured surface such as a piece of bark, corkboard, or even plastic mesh is necessary because house centipedes prefer to spend time clinging upside down and may prefer to molt in this position. I use corkboard since it is easy to cut to size, somewhat flexible, and feces or mold is easily scrubbed off the flat surfaces.

Scutigera coleoptrata on corkboard hide

    S. coleoptrata and T. tuberculata prefer moderately humid environments with dry surfaces to walk on. My clayish substrate holds moisture well, so I only add a small amount of water to it every two weeks or if it feels too dry to the touch. A wet, humid enclosure with condensation on the sides is likely too moist. Scutigeromorphs do best with a plenty of cross-ventilation in the sides of their containers. Use many small holes or mesh inserts since house centipedes can slip through surprisingly tiny spaces! Too much ventilation can also be dangerous as the enclosure should retain enough humidity to molt. Smaller centipedes probably need more humidity than larger ones.

    Both species of house centipede do well at room temperature. They are quite tolerant of heat and cold, although extremes of either are probably not survivable. Warmer temperatures encourage quick growth. You may want to keep them in a darker room as they are nocturnal and hide from light.

    Since both house centipede species I have get just over 1.5in/4cm body length, I house juveniles to small adults in ½ quart deli cups. The material is easy to poke pinholes in and the height is ample for molting. Adequately cross-ventilated cups also stack quite well to save space. Before offering well-ventilated deli cups with climbing surfaces I was never able to keep a house centipede alive for more than a few months, but my current specimens thrive under this method. However, the long terminal legs and antennae of larger adults may not always fit comfortably in that size of cup, and I’m still looking for a good substitute for the otherwise perfect deli cup.

1/2 qt. deli cup enclosure

Diet:

• Prey should be about ¼ of an individual’s body length or smaller.
• House centipedes prefer soft-bodied moths, flies, spiders over hard-shelled prey.
• I recommend feeding roughly once a week.

Scutigeromorphs use their long, flexible legs to literally lasso the limbs of their prey, restraining the arthropod so the centipede can deliver a quick-acting dose of venom. Accordingly, house centipedes show a strong preference for small, soft, and leggy prey such as spiders, moths, flies, silverfish and young crickets. Unfortunately, some of these animals aren’t practical to culture or available to buy as feeders. Crickets, red runner cockroaches, fruit flies, houseflies, wax moths, and firebrats are probably the feeders most available to buy or culture. House crickets and red runners grow too large for most house centipedes to hunt, so it's best to offer juveniles of these insects as prey. Waxworms can be fed and kept warm to produce adult wax moths for a hearty meal. Firebrats are heat-loving silverfish that probably make decent prey and are apparently simple to breed.

The common and easily cultured Blaptica dubia roaches and various mealworm beetle larvae are too heavy and shelly for house centipedes, although they might scavenge these species if pre-killed or chopped into pieces. Preferred prey like flies can also be fed if freshly killed (freezer) to prevent escape.


I feed mine a large amount of wild prey. Lawn pest crambid moths attracted to lights, house- and soldierflies from compost heaps, and indoor cobweb spiders are conveniently sized and readily eaten. Non-cultured prey carries a risk of exposure to pathogens, parasites, or pesticides and is also inconsistently available, but I regrettably do not have a reliable source of cultured prey. I’m working on rearing common pantry pest moths such as Pyralis farinalis and Plodia interpunctella for a more reliable source of moths and have had some success with them.

I feed my specimens about once per week, but I offer extra prey to skinny or recently molted individuals, and house centipedes in premolt will fast for 1-2 weeks before and after molting. Despite their relatively large eyes, scutigeromorphs require tactile cues to strike at prey. When tong-feeding, I grasp prey in fine forceps and gently tap the centipede's antenna or terminal leg with the prey item. House centipedes will refuse food if they are full, about to molt, or have just molted. A recently molted centipede will start eating again when it regains its normal coloration. Remove live, uneaten prey as soon as possible to reduce stress. Pre-killed prey can be left in for longer for them to scavenge at will, which is useful for easily frightened or recently molted specimens. Remove dead prey after a day to prevent mold. Centipedes produce droppings curiously similar to those of reptiles and tend to defecate in a set location. I spot clean my cups for feces weekly and wash the corkboard tiles about monthly with an old toothbrush. Springtail species (not isopods) that can handle drier conditions may be useful as a cleanup crew to reduce mold, but they cannot replace spot cleaning.

Growth & Breeding:

Scutigeromorphs display the unusual feature of anamorphic growth: they hatch from eggs with just 4 pairs of legs, and grow 1-2 pairs of legs with subsequent molts until they reach a total of 15 pairs. I have observed that Scutigera coleoptrata do not feed during the first few instars. Baby scutigeromorphs molt rapidly and might only eat 1-2 small prey items before molting again. Older juveniles and adults molt one to several times yearly. Adults continue to molt and grow past sexual maturity which is reached at around 1in/2.5cm (quite a bit smaller than the maximum size of either species). A feature common to centipedes but well-exemplified in scutigeromorphs is autotomy, or self-amputation of a leg or antenna in response to a predator grabbing the appendage. Scutigeromorphs can regenerate limbs and antennomeres in molting just as readily as they drop them. While you should treat house centipedes with care as they are delicate, missing legs can always grow back and hardly seem to slow them down. I once rescued a T. tuberculata from a spiderweb which tore off all fifteen legs on its right side. It ate live and pre-killed prey (with a tendency to chase them in circles) and grew back all fifteen in a single molt.

Unlike the more commonly kept scolopendromorph centipedes, scutigeromorphs do not brood their eggs and young. A mother house centipede uses her gonopods to bury her clutch of 30+ eggs in soil or crevices, coating them with soil particles and abandoning them afterwards. On the firm substrate I use, females oviposit in the shallow sand layer and gentle digging with forceps and a fine paintbrush should expose the eggs. They are hard-shelled and can be picked up with featherweight forceps to move into a separate cup. Eggs are best incubated under the same conditions as the adults. Since the first few instars do not feed, you do not have to worry about cannibalism, but they should be isolated soon prevent stress. These youngest instars can successfully molt standing on the ground, although as they grow more legs they will prefer to molt while hanging.

I have yet to successfully breed any pairs, but every female of reproductive size I caught in spring or summer was gravid. To mate, male centipedes deposit a spermatophore on the ground and lead the female to pick it up. Scutigeromorphs are the most easily sexed out of all centipedes: females have large, protruding gonopods which they use to manipulate their eggs; males’ gonopods are smaller and much less obvious. Since scutigeromorphs are not well-suited to hunt conspecifics of the same size, a pair can be cohabited for a while and observed to see if they mate. Keeping a male Scutigera coleoptrata with an already gravid female for too long resulted in her attacking and injuring him, likely because she perceived him as a threat.

S. coleoptrata pairing attempt; female at right

First post!

    I've been meaning to make a blog for a while now, so here it is. There will be more bugs here, and also more words. Most of the words will be about bugs. As promised, next post will be the house centipede caresheet!