KEEPER BASICS: BIOACTIVE ENCLOSURES

For an enclosure to be described as “bioactive” it must contain a micro ecosystem. This usually involves an inhabitant, a clean-up crew and organic material such as plants and leaf litter. Rotten plants and animal detritus are broken down by invertebrates and turned into rich, fertile soil, which feeds the plants. The plants then grow and provide shelter for the tiny organisms that reproduce within the enclosure quick enough to avoid being predated upon by the vertebrates within the setup. Although this sounds super complicated, herpetoculturists have used this husbandry method for decades and it is quickly becoming the most popular method of keeping for a lot of different species. With dedicated products available in most shops and a whole spectrum of clean-up crews to choose from, even the most novice keeper can produce a fantastic bio-active setup for a whole plethora of species.

Step 1: Layers

A ‘drainage layer’ is an area at the bottom of the enclosure that can hold water without flooding the substrate. This hidden reservoir of water encourages plants to grow their roots downwards in a natural direction. The layer can be created using a variety of mediums such as clay balls, volcanic substratum, sand or aquarium foam. These products are called “drainage mediums”. They are filled with holes that form refuges for beneficial bacteria to grow. Like an aquarium, the bacteria that grows in the substrate will help maintain the water quality and prevent any nasty smells. Whilst all drainage mediums have a similar purpose, each one has its advantages and disadvantages. For example, aquarium-safe foam sheets can be cut into the perfect shape to create pools of water and provide a platform for moss growth, but it is difficult to drain and prone to flooding. Clay balls will provide more room to collect water, reducing the frequency that the keeper needs to empty the tank, but they are heavy meaning the entire setup will need to be deconstructed to move it.

ExoTerra’s “Volcanic Substratum” is new and quite unique, it’s light and aesthetically pleasing but it is very fine meaning a lot of it must be used, increasing the price tag.

All drainage mediums should be rinsed with water to allow them to absorb water and remove any dust or debris. In a tropical enclosure, a deep drainage layer (several inches thick) will add to humidity, particularly if heated with an aquatic heating cable. In arid enclosures, the drainage layer needs to be completely water-tight and only a few centimetres deep. They are easiest to maintain in a glass vivarium, but not impossible to apply to a wooden enclosure. This is usually achieved by sealing the base with silicon or resin and lining it with a plastic sheet to capture all water. Any leaks will quickly damage the wood, so it is worth taking a lot of time and seeking out a lot of advice before turning a wooden enclosure “bioactive”.

Depending on the drainage layer, the keeper will most likely need to add some fine mesh to stop the substrate from falling into the drainage layer. There are a lot of options available and like the medium, different products have different pros and cons. Be sure to pick a size that is larger than the base of your enclosure. The idea is that the top layer will be filled with substrate and nothing should fall through into the water section. Having a few extra centimetres of mesh around the perimeter of the substrate will help capture any loose strands of coir or extra fine soil. The Lucky Reptile Hydro Fleece is our favourite product for this. It’s super fine, meaning no solids can pass through it and when wet, it condenses to a thin layer around the substrate that serves its purpose without being too overbearing. It may look like a huge sheet of cotton wool in the vivarium, but once soaked, it’s extremely subtle.

Some keepers will also add charcoal or slate on top of this divider before adding their substrate. This helps with the gas exchange through damp substrates. By creating pockets of air, it provides a haven for clean-up crews and allows easy passage for rooting plants.

Step 2: Substrate and leaflitter

Once the drainage layer has been established and an appropriate barrier has been installed, it’s time to add the substrate. This will vary according to each species’ requirements but must be comprised of several natural components. For example, arid setups may require a mostly sand-based substrate, but soil and coir will assist in plant growth. Tropical substrates are much more soilbased but with orchid bark and charcoal to aerate the layer, whilst using moss and coir to retain water. Many keepers will mix their own substrates, but Bio Life and Bio Life Desert are excellent store-bought blends with great component ratios.

A key component that should be used in every tropical set up and should be utilised in many arid setups is leaflitter. All terrestrial rainforest species will encounter leaf litter at some point. It provides microclimates and shelter for small animals, as well as sensory enrichment and burrowing opportunities for larger animals. Leaflitter also helps provide higher humidity and contributes to a natural-looking biome. However, the most important function of leaf litter within a bio-active enclosure is to feed the clean-up crew. Without organic matter for the clean-up crew to feed on, they will soon perish. In our opinion, very few keepers (even the most reputable of online educators or long-term experienced breeders) use enough leaf litter in their enclosures. In the rainforest, terrestrial animals are exposed to 5, 10, maybe 15+ inches of leaf litter at a time. This leaf litter dries, is soaked, rots and replenishes at different rates across the forest, producing extremely valuable niches for the animals to move between. This is especially important for reptiles, amphibians and invertebrates. Remember that this leaflitter, once wet, will reduce in size, so it is okay to go a little “overboard” with leaves when recreating the amazon. It is at this point when the clean-up crew should be added, amongst the leaves and substrate.

Step 3: The clean-up crew

To establish a functioning ecosystem, clean-up crews are required to break down waste to a suitable size for microorganisms to break it down completely. There is a vast array of species that fill this niche, but for beginners, springtails (Collembola sp ) and isopods tend to be the go-to. Advanced keepers can utilise millipedes, beetles, earthworms and various other detritivores (waste munchers) to do the job. Some of these species will breed prolifically, consume waste at different rates, or become food for the inhabitants so it’s best to have a bit of experience tending to a bioactive setup before these are used. The novice, however, should consider a healthy amount (perhaps one or two pre-packs) of springtails, plus one culture of isopods for a 45x45x45 terrarium or taller. For enclosures with a larger footprint, try adding some extra isopods as these are good indicators that your bioactive ecosystem is functioning well and a low density in a large enclosure can mean that you never see them again.

Springtails (Collembola sp.)

These are tiny hexapods that are found across the world. Collembola is actually one of the ancient lineages, that are no longer considered ‘insects’ and date back almost 400 million years. Because they are found all over the world, they are extremely adaptable and excellent for both tropical and arid setups. They can be cultured within a pot of charcoal and water and provided with grains of dry rice (which then produce mold for the springtails to eat). Of course, if a bioactive set-up is healthy with a good amount of leaflitter or fungus, a single colony of springtails should thrive for many generations.

Isopods: There are various genera of isopods readily available as clean-up crews but not all will flourish in all environments.

Clown isopod (Armadillidium klugii)

Clown isopods are easily recognised for their bright markings which are thought to be a form of mimicry of the Mediterranean black widow, to deter predators. They come from the coastal areas along the Adriatic Sea, notably Croatia and Montenegro. They are usually found beneath stones and in crevices, where they seek humidity. That being said, these isopods are generally considered a good all-around generalist species, so long as a humid area is available in your bioactive somewhere – which is usually the case even in an arid setup. They reach a maximum size of 21mm and will eat pretty much any organic material available.

Granulated isopod (Armadillidium granulatum)

This species is also a safe choice for almost any bioactive, favouring a 50:50 dry and moist environment. Keeping the humid area of your enclosure maintained will provide a good refuge for these isopods. They don’t like to be too wet, so they likely won’t be ideal for a tropical setup that needs frequent heavy misting. Younger individuals may be eaten by inhabitants, but they are a fairly large species when adults. They also sport quite an appealing colouration of yellow splotches.

Bioactive Enclosures

Pill isopod (Armadillidium vulgare)

These are the common woodlice we see in Europe and the UK. They are hardy and tolerant of some dry conditions, so they should establish well in a tropical or arid setup as long as conditions aren’t too extreme on either end. While the wild type is a bland slate grey, there are a few colour morphs now available thanks to captive breeding, including red, yellow, albino, “orange dalmatian”, or “magic potion”. Whatever the colour, they will all do the same job in the end.

Dwarf tropical white isopod (Trichorhina tomentosa)

These are usually said to be the most common species chosen for tropical setups with high humidity. Dwarf whites are soft bodied isopods that do not roll into a ball, and reproduce asexually. They are small, but hard workers; efficiently cleaning up detritus from the soil and other areas of the environment. T. tormentosa are most popular for keeping alongside amphibians such as poison frogs.

Giant canyon isopod (Porcellio dilatatus)

These are an excellent choice for arid setups, so long as a small humid retreat is available. P. dilatatus come from Western Europe and North America, and they grow quite large, owing to their name. They eat organic matter similar to most other isopod species and reproduce at a moderate rate. They don’t have a flashy appearance, but are a good choice for their hardiness in drier setups and affordability.

Speckled isopod (Porcellio scaber)

P. scaber is another common species found throughout Europe and with different colour morphs – such as the popular orange and “dalmatian” varieties. These isopods need 70-80% humidity to thrive and therefore will not do well in an arid environment with low humidity levels. They eat and breed well in captivity.

Lighting and heating

Lighting and heating are both very important components for any set-up. These have been covered in much more depth in past ‘Keeper Basics’, but there are some key considerations when applying them to a bioactive setup. Firstly, plants photosynthesise best under red and blue light, meaning LED lighting is almost essential for good plant growth. UVB and spot bulbs will also naturally dry out an area in the enclosure, so this should be considered when the flora is being planted. Heating should always come from above, or, if a heat mat is used, try to install this to the side of the terrarium. A heat mat sitting underneath a drainage layer will not fair well once the drainage layer fills with water. In this instance, heat cables are sometimes installed behind the artificial background to raise ambient temperatures slightly. This will require a good amount of planning prior to creating the enclosure to ensure the electricals can be changed and replaced if needed.

Maintenance and plant choice

Although bioactive enclosures are supposed to be “selfmaintaining”, there are a few things a keeper should do to ensure they have a healthy enclosure. The most important thing (aside from the general upkeep of the inhabitants) is to keep an eye on waste build-up. Sometimes cleanup crew cultures can ‘crash’, meaning they are no longer reproducing. This might happen because they have got too hot or too cold or the population density was not appropriate or, in the most likely scenario, they have been eaten. This can be combatted by introducing more custodians, commonly referred to as a ‘bio shot’.

Plant choice is an entirely different subject. To address horticulture in a bioactive guide would be to criminally understate the vast possibilities available to the keeper. Instead, the keeper should seek advice on what plants would be most appropriate for their animal. Most (but not all) plants sold by a reptile shop will be non-toxic and reasonably hardy. They are typically grouped into “tropical” and “arid” and although there are some species that are more challenging to work with, or require more specific positioning than others, most should be considered “beginner” plants. That being said, what works for one keeper may not work for the next and without horticultural advice, it is very difficult to define what is going wrong. In this case, try to stock as many plants as possible and do not be afraid to add more. Expect that some will wilt and die which is actually very beneficial to your bioactive enclosure and its inhabitants, but less beneficial to your purse. Beginners should begin their hobby by selecting a broad range of affordable plants, rather than being drawn towards that one pretty orchid that could very quickly become isopod food.