Substrate for Isopods

Many people come into the isopod hobby because of an interest in bioactive enclosures, and with experience in the care of some rather finicky animals such as frogs, geckos, and roaches. Due to this, most people have very high expectations of what substrate to use, fearing the worst of what is commercially available and that it will harm their animals. While some options can be harmful (even those that are typically recommended for the pickier animals!) sourcing a cheap substrate source for isopods isn’t as difficult as many would believe. Many people choose to make their own substrate mix; so, we will discuss different ingredients that may be used, as well as commercial mixes available.

A cute little P. dilatatus butt can be seen poking out of one of the many burrows of this species

The best advice to consider when selecting a substrate for isopods is to treat them like expensive, sentient plants. A proper substrate provides not only a home for isopods, but also serves as a food source. No isopods can live exclusively off substrate, but a nutritious substrate that allows for burrowing and moisture retention is a key aspect of a healthy, thriving colony.

The first go-to that people usually grab at is coco fiber or coco husk. Lots of people have this on hand because it is a sterile material that is cheap, widely available, and easy to find. It’s immensely popular for reptiles, amphibians, and invertebrates alike so keepers of all types are very familiar with it. Coco husk is useless for animals like isopods, however, because it does not retain moisture well, does not maintain burrow structure, and has no nutritional value. Isopods won’t eat and break it down like other substrates and cultures kept on coco fiber are comparatively weak to those kept on other substrates, with increased risk of collapsing entirely. Coco fiber can be used as an additive to substrates in instances where the volume is lacking but should never be used on its own.

Sphagnum moss has many uses.

Sphagnum moss is a popular item to add to substrate mixes. It is a renewable resource grown in bogs that is widely used with plants such as orchids. We use sphagnum when packaging and shipping isopods. The most important aspect of sphagnum that makes it so attractive is a system of capillaries that absorb and distribute water – this provides a constant source of hydration to isopods in an enclosure and reduces the risk of the colony dying from drying out. Some people place a pile of sphagnum in the corner of the setup and wet that area; others mix it into the substrate. Isopods will eat sphagnum, but it is a very dense material and takes a long time. Sphagnum is not an absolute needed component for a healthy tub, but it is a good resource for new keepers concerned about their tubs drying out.

Similar in origin, peat moss is another item used in substrates. There is some debate over the use of peat moss because the product harvested and distributed is not the live peat moss, but old, buried peat moss that is dug up. It is a nonrenewable resource containing large amounts of carbon and its harvest is believed to be driving climate change. It is a highly nutritious mix popular in use with plants and on first inspection, looks like fluffy dirt. Isopods do well with peat moss as an exclusive substrate.

I just plucked this out of an old bio setup that is 5 years old. It's so clunky it floats to the top.

Charcoal is considered an important part of bioactive substrates; it helps combat the smell of bacteria from standing water, and springtails love it! Isopods do not get any benefits from charcoal though, so it is a largely unnecessary additive. Isopods will die from excess standing water long before charcoal warrants any benefits, and isopods do not eat or derive any nutritional value from charcoal. Since the isopods do not eat the charcoal, it remains behind when frass (waste or bug poop) is removed, and the substrate becomes clumpier over time. Springtails will establish themselves and eat several other food sources without the addition of charcoal.

Fun fact: perlite is a very popular hatching medium for reptile eggs.

Perlite is an ingredient keepers try to avoid. Perlite, while not inherently harmful, has no nutritional value and only functions as a soil expander. It is the result of superheated volcanic glass that reached the point it has “popped” like popcorn. Perlite is filled with tiny air pockets and is an asset in potting soil because these air pockets both encourage water retention and drainage, so in this aspect it is more useful than charcoal. Perlite does pose a problem for the same reason as charcoal, because when the frass is sifted from the substrate the perlite remains and builds over time. Perlite is typically small and in minute quantities, so if a mix contains perlite this does not mean it should necessarily be avoided.

A component keepers frequently inquire about adding to their mixes is sand. Unless the isopod species is native to a dry or sandy area, sand doesn't pose much benefit when being added to a mixture. Sand is typically a silica mix and offers little to no nutritional value. Sand can add structure to a substrate mix, holding burrows intact. Something to keep in mind is that sand will increase the weight of an isopod culture considerably.

Earthworm castings is a resource that is great for both volume and nutrition. Isopods positively thrive on the waste of other animals, invertebrates included. Earthworm castings on their own pack down, and cannot be used exclusively, but work well mixed into other substrate components. Similarly, leftover substrates from roach, cricket, and millipede enclosures are coated in the wastes of the insects and isopods go bonkers for it.

Flake soil is a product made for millipedes and many species of beetle that need rotten wood to survive. Flake soil, similarly, is particularly valuable for isopods that depend on rotten wood to survive, like many giant Spanish Porcellio. All isopods do benefit from rotten wood, so the nutrition that flake soil offers is beneficial to all species. Flake soil can be either made at home from a mix of water, bran, and sawdust, or purchased from online retailers. It isn’t suitable as a stand-alone substrate because it is both expensive and tends to mold.

ABG (Atlanta Botanical Gardens) substrate is what many people defer to for naturalistic and bioactive setups. Isopods do well on ABG, but it does have a high charcoal content which is a pain over time. ABG can be an unrealistic substrate for keepers that have multiple, large enclosures because it is expensive.

Topsoil is a cheap option to offer isopods, for as low as $2 for 5lbs. Topsoil is what we initially started keeping our isopods on. Topsoil is popular in landscaping, because it does have some nutrition, and is readily available in bulk. However, topsoil is not enriched and does not have any soil expanders added, so compacts easily over time.

For commercial substrate mixes, what we recommend is Jungle Earth produced by ExoTerra. Jungle Earth has a perfect balance of moisture retention, nutrition, and best of all, no charcoal! It is available in large bags as well. We have tried other commercial mixes and our cultures have done best on this mix. There are also many commercial substrates available on the market for invertebrates, it is best to avoid those tailored to roaches, dry species, scorpions, or tarantulas and use those for millipedes or even isopods. Read labels carefully if vendors supply them.

This potting soil has perlite, but for the price you can't really go wrong.

Substrate for isopods doesn’t have to be limited to products specific for animal use; often these are repackaged from the plant trade with a more expensive label. Many potting soils have everything that isopods need, and even are safe and effective for use with reptiles. Initially, the labels on potting soils can be intimidating because of the ingredients listed, but just because something is unfamiliar doesn’t mean it is bad. One thing to avoid in potting soils is plant food additives or Miracle Gro. Plant food typically presents in substrates as round yellow or green balls filled with a liquid. These liquids are manufactured with the intention to burst over time and provide nutrition for plants. If being used in a reptile terrarium, it may poison reptiles that consume them or be harmful to the keeper’s skin, causing chemical burns. Potting soils available varies regionally based on where keepers are located, so we cannot recommend a specific brand.

Most of those scary additives in potting soil are largely beneficial to isopods for their nutritional value. Mycorrhizae, for one, seems intimidating because of its role as a root fungus (and who likes fungus?) but isopods love mycorrhizae and many species positively thrive with it available, lining burrows with it for their young. Potash is a natural compound added to soils for the potassium content. Some potting mixes say “natural fertilizer”- this means animals waste or poop, not liquid plant food. Limestone is added to many due to calcium it offers. There are several organic soils available on the market, many of these are exclusively worm castings or peat moss and overpriced, so read labels carefully.

Potting soils may use all, only a select few, or even more ingredients than we have discussed in this article. When in doubt, break down the package label by ingredients and search what they are one at a time. When buying substrate, you can save a lot of money by carefully buying soil intended for plants that work just as well, if not even better, than substrate made specifically for animals.