Choosing the Right Substrate for Your Tarantula

Pick your poison…

Since getting into the hobby, I’ve spent a lot of time (more than I’d like to admit) experimenting with various substrates. When I bought my first T about 18 years ago, the popular choice for spider bedding was dry vermiculite. A lot has changed since then, however, and better (and more appropriate) options are now recommended.

Ask any group of tarantula keepers what material they choose to keep their prized pets on, and you are likely to get a variety of responses. A recent poll on the Arachnoboards forum did reveal that there are a handful of popular choices that tarantula keepers mix and match to get the properties they desire. Much is up to personal choice, and I actually find it quite fun to experiment with different combinations.  What follows is a list of some of the more popular choices as well as some pros and cons of each.

COCO FIBER (Eco Earth)

Coco fiber

Made from ground up coconut husks, and sold loose in bags or in compressed bricks, coco fiber substrate has become one of the most popular substrate choices for those who keep tarantulas. Although the bags save you the effort of having to re-hydrate the compressed bricks, they are much more pricey. Zoo Med’s Eco Earth is probably the most popular brand, but other companies also produce the bricks (and some are less expensive).


  • Fairly inexpensive if you purchase it in bricks. Buying bricks in three packs makes it even more affordable. ($7.99-$9.99 for about 21 liters)
  • Absorbs water well for species that need some moisture.
  • Great when used dry for arid enclosures.
  • Seems to resist mold.


  • Can become expensive when filling larger enclosures.
  • Re-hydrating the bricks can be a bit time consuming and messy.
  • Re-hydrated coco fiber has to be dried out before being used in an arid enclosure (I put mine in a large foil turkey pan, then slowly bake in in an oven at about 250°, watching it at all times)
  • When dry, it can be “fluffy” and more difficult for burrowing species to create homes.
  • Dries out quickly (could be a positive with arid species)



Regular old run-of-the-mill topsoil can be a great and inexpensive substrate choice. It can be purchased at any Walmart, Home Depot, or Lowe’s in large bags for only a couple dollars. If using topsoil, it’s important to make sure that it’s organic with no fertilizers added (this includes animal waste). I have found myself using top soil mixes more and more due to the cost-effectiveness, availability, and water retaining qualities. It should also be noted that many European hobbyist have been using regular topsoil from their yards for years with no ill effects.


  • Very inexpensive (a .75 cubic foot bag runs about $2.25).
  • Easily procured.
  • Mixes well with other substrates to get desired properties.
  • Packs down well; good for burrowing species.


  • Inconsistent quality. Often comes with jagged chunks of branches and wood chips that must be filtered out
  • Very heavy when used to fill larger enclosures.
  • If used straight up, spraying/moistening of the substrate can create puddles or mud. It does not absorb water as well as other substrates.



Peat moss is another readily available and inexpensive substrate alternative. Again, it can be purchased in a variety of places, and the large bags are very convenient for filling up large enclosures. As with the top soil, you want to go with a product that is organic and contains no fertilizers.


  • Very inexpensive and comes in large quantities (a 3 cubic foot bag is only $9.99)
  • Packs and forms very well for burrowing species
  • Absorbent when wet down for species requiring moisture.
  • Mixes well with other substrates.


  • Can be a bit dusty if used dry
  • Like top soil, the quality from bag to bag can vary. Large chunks or sticks must be filtered out.
  • Can be prone to growing mold or fungus.

As stated earlier, these three are the top choices among enthusiasts, and each can be used alone, or they can be mixed and matched to create a substrate to fit any need. For the majority of my enclosures, I’ve been using a 50/50 mix of coco fiber and peat moss. This has become my “all-purpose” substrate for many of my specimens.

VERMICULITE (As an additive)


Although the days of using vermiculite as a substrate for my Ts are long over, that is not to say that it can’t be very useful. For species requiring more moisture, I put a 1/2″ thick layer of vermiculite on the very bottom of the enclosure, then mix some in with the 50/50 coco/peat combination and use that to fill the rest of it. I find that the vermiculite retains water better than coco or peat alone, and allows for better water percolation. This enables any water I pour in to filter down to the bottom, keeping the lower levels humid and moist like the tarantula’s burrow in the wild. For Ts requiring more humidity, this also allows the water to evaporate more slowly, elevating the humidity inside the enclosure as it does.

The trick is to not add too much, as overdoing it keeps the soil “fluffy” and prevents it from being packed down well. Vermiculite is relatively inexpensive (an 8 quart bag costs about $3.99), and I always keep some on hand.



Sphagnum moss is another useful additive when you are trying to maintain humidity in an enclosure. Moss absorbs water like a sponge and holds onto it quite well. When used inside an enclosure, it can be wet down to provide a source of humidity. I like to place some around water bowls to soak up the overflow. Although various mosses are produced by reptile supply companies, clean organic horticultural moss can also be purchased at Walmart, Home Depot, Lowe’s, and gardening supply stores.

Some things to avoid when experimenting with substrates:

Anything with jagged sticks or pieces. These could be harmful to the tarantula, as a falling T could rupture its abdomen on something sharp. If you buy substrate with jagged pieces, they must be removed before use.

Substrates with with fertilizers or additives. Make sure to check the labels before you buy. Even some “organic” soils have natural fertilizers added, including animal waste.

Pine chips or products made from cedar. Compounds in conifers and cedar are suspected to be harmful to Ts (Note: it is widely believed that mulches or peat mixes containing pine or cedar products are safe)

Aquarium Gravel. Although used for years, its use as a substrate is now generally frowned upon. Besides holding water too well (it tends to puddle and stagnate beneath the surface), it can trap a tarantulas leg or prove hazardous in a fall.