How to Build a Bioactive Enclosure

Bioactive setups are characterised as a self-maintaining ecosystem which demands the breakdown of detritus such as animal waste, and in turn, creates fertile soil for plant growth. Despite a surge in popularity in recent years, these enclosures are nothing new. They have been widely used by herpetoculturists for decades before the sterile keeping trends of the 90s and 00s. Nowadays, creating a bioactive enclosure is much less specialist, with dedicated products available in most shops and a whole spectrum of clean up crews to choose from. A basic understanding of the components required to build a bioactive enclosure is required, but once established, they offer a rewarding approach to animal care. Here’s our step-by-step guide to going bioactive…

 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 is important for plant growth and encourages plants to grow their roots downwards in a natural direction. They can be created using a variety of mediums such as clay balls, volcanic substratum, sand or aquarium foam. A drainage medium with lots of holes for beneficial bacteria to grow will help maintain the water quality and prevent any nasty smells, but each medium has its advantages and disadvantages. For example, aquarium foam can be cut into the perfect shape to create pools of water and will host a whole spectrum of aesthetically pleasing mosses. However, clay balls will provide more room to collect water, reducing the frequency that the keeper needs to empty the tank. 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, usually hosted in a wooden vivarium, the drainage layer needs to be completely water-tight and only a few centimetres deep. This is usually achieved by using silicon or resin and supported with a plastic sheet to capture all water, as leaks will soon damage the woodwork.

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. Some keepers will also add charcoal or slate before adding their substrate. This helps with the gas exchange through wet or 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 leaf litter

Once the drainage layer has been established and an appropriate barrier has been installed, it’s time to add the substrate. This will vary across species and enclosure set up 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 soil-based, 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 Forest 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 leaf litter. 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. Leaf litter 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.

Step 3: The clean-up crew

To establish a functioning ecosystem, clean-up crew are required to break down waste to a suitable size for microorganisms to break it down completely. There are 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 a bioactive setup before these are used.  

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 mould for the springtails to eat). Of course, if a bioactive set up is healthy with a good amount of leaf litter or fungus, a single colony of springtails should thrive for many generations. A common issue brought up with those new to bioactive setups is the worrisome appearance of fungus or moulds. This is a normal part of the cycle that springtails will quickly take care of. What’s more, mushrooms in the soil are seen as healthy soil indicators and they will die off and break down for your clean-up crew in a short amount of time.

Isopods

There are various genera of isopods readily available as clean up crews but not all will flourish in all environments. They will generally thrive off the detritus build up in the enclosure, but to get isopods extra healthy and breeding, they should be given small amounts of a calcium and protein source. These include high protein vegetables, good quality fish flakes, sheds/waste, and cuttlebone or crushed eggshell 1 – 2X per week. In some cases, the inhabitants will also benefit from these, but for more sensitive species maintaining a separate isopod colony in a plastic terrarium can be an easier option. This prevents them being preyed upon too quickly, as they can be gradually added to the bioactive enclosure.

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-round 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 large species when adults. They also sport quite an appealing colouration of yellow splotches.

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 like 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.

Dairy cow isopod (Porcellio laevis)

The dairy cow isopods are some of the most popular and voracious of all the isopods. They will quickly eat large amounts of detritus, including shed skin, making them ideal for setups with larger inhabitants such as colubrids. 

Clown isopod (Armadillium klugii)

 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 articles, 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 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 fare 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 before creating the enclosure to ensure the electricals can be changed and replaced if needed.

Maintenance

Although bioactive enclosures are supposed to be a self-maintaining ecosystem, 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 clean up crew cultures can ‘crash’, meaning they are no longer reproducing. This can be combatted by introducing more custodians, commonly referred to as a ‘bio shot’. Of course, plants will need to be watered and pruned depending on the type of set up. Tropical set ups should always have some water in the drainage layer to feed the roots. Increased spraying or pouring water directly into the drainage layer will support this.

The finished bioactive enclosure with two blue poison frogs (D. tinctorius)