Sexing

There are three main ways to determine the gender of your tarantula:

• Sexual maturity
• Presence of Epiandrous Fusillae
• Looking inside the molt

Male Aphonopelma sp.

The main reason you would like to determine the gender of your tarantula is if you want to keep your pet for a long time. But you also have to consider that their longevity makes it likely you will pass it down to the next generation. Keep in mind that if your tarantula is a male, it will probably reach the end of his life in about four to six years, which is pretty long. However, a female could live up to 10 to 30 years, depending on the species.

I can recommend, though, that you buy more than three spiderlings (baby tarantulas) to increase the likelihood of getting the gender you want.

Sexual maturity

You will never be able to tell when a female reaches sexual maturity, unless you bring a male close to her and she becomes receptive, instead of eating it as she would if she wasn’t mature.

When a male matures sexually, he will undergo radical changes, and he will only have about a year more to live.

Males experience physical changes that can be easily seen. The main one is that a pair of small appendages called spermatic hooks or copulating bulbs grow on the tip of the pedipalps. These will be used during copulation as described in the section on Biological Cycle and Reproduction.

Spurs and hooks on Brachypelma vagans.

Spurs and hooks on Grammostola rosea.

In plain sight are the small boxing gloves on the tip of the pedipalps. Another new feature they grow are the tibial spurs that, as their name suggests, are a pair of hooks that grow on the tibia section of the first set of legs. These will be used to hold down the female’s fangs. There are some exceptions and this feature is not present in all species; that probably means that they have a more tranquil and less aggressive ritual than species that do.

Another characteristic is that the adult male is no longer “chubby”, and becomes slender and very attractive. He will be very active in searching for females, so he can’t afford the excess weight that can cause him to get hurt during this search.

In this link you can find various spermatic hooks of other species.

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Presence of Epiandrous Fusillae

This can be the hardest way to determine the tarantula’s gender, but in time it can become easier, and very useful.

The Epiandrous Fusillae are tiny spinnerets that are able to produce a very special silk that does not have capillarity. This silk will be used to make his spermatic web, just as described in the section on Biologic Cycle and Reproduction. These can come in various shapes - they can be in the shape of a dark triangle, half-circle, or diamond – and are located on the epigynium or genital groove. The following are some examples:

I recommend that you visit Rick West’s page where you can download a PDF article on this subject, and I also recommend this page that has a bit less information, but is in Spanish.

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Looking inside the molt

This is the easiest way to determine your tarantula’s gender. All you need is patience, a lamp, and a magnifying glass.

What you have to look for in the molt is the presence or absence of the spermatic sack or spermatheca on the inner part of the opisthosoma.

Unfortunately, this is the softest part of the molt, and it shrivels once it dries. But you don’t have to worry, even if it’s dry, pour a few drops of water on it, and it will be pliable again in a few minutes.

You need to extend this part very gently, and look between the four book lungs for the presence or absence of the spermatheca. If it is not there, you have a male, and if it is, then you have a female.

The shape of the spermatic sack changes as the tarantula grows, but if you can’t find anything at all, it is most definitely a male.

This is very simple, and to make it easier for you, I show some pictures here that can help.

In this link you can find many pictures of spermatic sacks of different species.

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