Tarantulas are often split into multiple groups by keepers, one of them describes how a tarantula naturally prefers to live and its behavior. Some tarantulas might not totally fit within each group and may appreciate an enclosure that mixes two of them. However, fossorial tarantulas normally dislike and won’t use any kind of arboreal additions to their setup.
Fossorial tarantulas are burrowing species that need deep substrate and don’t spend much time on the surface. They build their burrows deep under the ground and need the substrate to be at least 1.5x deeper than their leg span. Fossorials usually appreciate a taller/narrower enclosure for extra digging room.
Knowing what type of tarantula you have is important to meet all their needs. Giving a fossorial species an enclosure better suited to an arboreal will make them very stressed which then causes health problems. Knowing what fossorial means before getting your first tarantula will save you and your new pet a lot of trouble.
What are Fossorial Tarantulas?
Fossorial tarantulas live in burrows underground and don’t venture outside on the surface very often. They can be confused with terrestrial species sometimes since some terrestrial species also live in burrows but those don’t dig down as deep. In some cases, it’s common to never see your fossorial tarantula since they live almost entirely underground.
These are burrowing species who want an enclosure where they dig down deep to make their ‘house’ for them to live in. For the most part, they will not leave their burrow. After completing their burrow, some species may wander outside on occasion and others may prefer to molt outside of their burrow. Others will molt inside and push their old exoskeleton outside instead.
Fossorial vs Terrestrial Tarantulas
Terrestrial tarantulas generally live most of their lives at ground level as opposed to underground or off the ground. They can be easily mixed up as fossorial species by inexperienced keepers who don’t fully understand the differences between them. Terrestrial tarantulas might make burrows below the ground but these are not very deep and are much more likely to be seen walking around outside.
The flip side of this is that fossorial tarantulas will dig deep under the ground to make their burrow. They will spend almost all their life below the ground.
Fossorial vs Arboreal Tarantulas
Arboreal tarantulas do appreciate tall enclosures but for a different reason to fossorial tarantula species. Those who naturally live above the ground in trees are considered to be arboreal tarantulas since they also create burrows above ground level. Arboreal species don’t spend much time on the ground and very rarely do any digging. There are always individual differences where some people report their arboreal species has decided to become fossorial for a bit but this isn’t very common and should not be considered normal.
Fossorial tarantulas prefer tall enclosures not for the height but for the depth. Tall enclosures can be filled with a lot of substrate. This makes them perfect for both fossorial species who appreciate the depth and arboreals who can make use of the extra height.
Can a Tarantula be Fossorial and Terrestrial or Arboreal?
Some species of tarantula are known to be semi-arboreal and semi-fossorial. This means while they aren’t totally fossorial, arboreal, or terrestrial, they display a range of behaviors across their lives which means they benefit from a mix of both.
The skeleton tarantula (Ephebopus murinus) is considered to be semi-fossorial and a terrestrial species. This means they appreciate both a deep enclosure with lots of substrate and also space to roam a little.
How do Fossorial Tarantulas Hunt?
Tarantulas who live underground are passive hunters. Fossorial species wait for prey to pass their burrow before striking and taking them down into the burrow to eat. These tarantulas will wait near the entrance to the burrow for potential prey to come close. When you see some tarantula legs poking out of the entrance, they’re waiting for prey to come to them. These tarantulas will not usually hunt on open ground and will not venture very far if they do.
They hunt similarly to fossorial spiders who also don’t leave the burrow often. Trap door spiders will spring out of their burrow and attack prey that comes close to take back down into their burrow. Fossorial tarantulas hunt similarly with a surprise attack on prey who come close before taking it down into the burrow.
How to feed a Fossorial Tarantula
Feeding a fossorial tarantula is simple. While it might seem like a tarantula that lives underground would be difficult to feed, the process isn’t complicated. Your fossorial tarantula will tell you when they’re hungry and actively looking for food. When you see them close to the entrance of the burrow or see their legs poking out, this means they’re waiting for prey.
Placing the food near the entrance to their burrow is ideal for them. The food will immediately be in their attack range and will quickly be grabbed. If the tarantula wants to eat they will attack the prey and take it down into their burrow. Otherwise, they will ignore it or just kill it if it comes too close to them.
Putting the food close to them gives the tarantula the option to take the food quickly without needing to wait for the prey to finally wander close enough to their burrow. Placing it inside their burrow can be stressful to the tarantula. For a fossorial species, it can be hard to know when they’re in a molting period. This means you could put them in a dangerous position if they’ve recently molted in the safety of their burrow.
The safest way to offer a fossorial tarantula food is to put it near the entrance of the burrow and remove it if the tarantula shows no interest.
Examples of Fossorial Tarantulas
1. Skeleton Tarantula (Ephebopus murinus)
This species is aptly named the “skeleton tarantula” due to their dark colors and white highlights on their legs that look similar to bones. A new world species from Brazil, they grow quickly and are known to appreciate a deep enclosure to burrow. While they have some fossorial characteristics, they will also explore the surface too making them a semi-fossorial species.
2. Trinidad Dwarf Tiger (Cyriocosmus elegans)
Reaching only 5cm max, this dwarf tarantula is a new world species from South America, Trinidad and Tobago. They might not be exclusively fossorial but this species appreciates a deep enclosure with lots of substrate and some of them appreciate some extra height for climbing too. Many individuals are explorers despite living in deep burrows which also makes them relatively active on the surface too.
3. King Baboon (Pelinobius muticus)
The King Baboon is a large tarantula where females can grow to over 7” in size. They’re a burnt orange color and should not be confused with the brighter colored Orange Baboon Tarantula which is commonly talked about in the hobby. This species comes from Africa and is an old world species which means they lack urticating hairs but are more prone to biting. However, it’s also entirely fossorial meaning that most keepers rarely ever see this tarantula leave their burrow.
Due to the size of this tarantula species, they are capable of eating mice and other similar-sized mammals, amphibians, and birds. The healthiest diet for them is predominantly insect-based with the occasional larger meal which mimics their natural wild diets.
Species Commonly Mistaken as Fossorial
Some species are commonly thought to be fossorial due to them being opportunistic burrowers and often digging down into the substrate. While they can live in burrows, it’s not their usual choice of home in captivity and their behavior doesn’t quite fit in with typical fossorial species.
1. Chilean Rose Tarantula (Grammostola rosea)
Interestingly, this species is fossorial in the wild but in captive settings, they act more like a terrestrial tarantula. In the wild, they will live in deep burrows where they remain for most of their lives but captive Chilean Rose Tarantulas are more willing to be exposed on the surface. While they don’t need a deep enclosure to be happy, giving extra substrate lets them burrow deep down if your tarantula decides they want to be fossorial.
In captivity, the Chilean Rose Tarantula is a terrestrial species but in the wild, they’re mostly fossorial!
2. Orange Baboon Tarantula (Pterinochilus murinus)
Nicknamed the “Orange Biting Thing” in the hobby, the OBT is an old-word species from Africa that is an opportunistic burrower. They’re usually considered to be a terrestrial species that is happy to live in a deep pre-made burrow but they’re also semi-arboreal. Orange Baboon Tarantulas are happy to spend a lot of time off the ground, on the ground, and will live deep under the ground when the opportunity presents itself.
It’s very easy to mistake them as fossorial or arboreal but in reality, this species is terrestrial.
3. Giant White Knee Tarantula (Acanthoscurria geniculata)
Some new keepers can mix up the Giant White Knee with the Skeleton Tarantula due to their similar color patterns. The Giant White Knee is also dark-colored with white stripes on the legs however, the pattern is less “bone-like”. They’re a largely terrestrial species but they’re also known to burrow when the mood suits them. Keepers are usually advised to give them a big and deep enclosure with plenty of substrate so they can burrow as much as they like.
Just because a tarantula is known to burrow and may prefer living in a burrow instead of a hide does not mean they are fossorial.
A better understanding of fossorial tarantulas will make your life much easier as a tarantula keeper and reduce a lot of stress. True fossorial species are unlikely to leave their burrows and there’s a good chance you’ll have a “pet hole” because you may only see the tarantula a handful of times. If you’d like a fossorial tarantula that does sometimes leave its burrow then consider looking into semi-fossorial species instead.
Caring for a fossorial species is simple. Just ensure the enclosure is big enough for them and deep enough then fill it with as much substrate as possible. Remember to not put food into their burrows and remove any food they aren’t interested in.