This is often one of the biggest questions that goes through a keepers mind when acquiring a new tarantula. Females are prized among hobbyists for their larger size, longer lifespans (some species can live decades!) and ability to produce eggsacs. Males are often requested for breeding projects or for those who want a pet with a lifespan (and commitment) of a only few years. Determining the sex of a tarantula can be tricky though, especially when it is younger as male and female tarantulas will often look and act extremely similar until mature.
How can you determine the gender of a tarantula?
The ONLY way to absolutely know the gender of a specimen is to look at it’s molt/exuviae.
The other, and not so reliable method is by looking at the tarantula itself, either ventrally (underside) or dorsally (topside) which we’ll cover later in this article.
What about spiderlings?
With over 35 years combined tarantula keeping experience we still do not know of any method to determine the gender of spiderlings. If we come across even semi-reliable method to sex spiderlings I will update this article with instructions.
So how do I molt/exuviae sex a tarantula?
By using the tarantulas exuviae (also: exuvium) also known as a cast skin or molt. Exuviae sexing, also known as molt sexing is the most reliable way to confirm the gender of a specimen and the only tried and true way to absolutely confirm the sex of larger, immature or mature specimens. In order to properly determine the gender first you will need an intact molt.
Getting an intact, read-able molt is a feat in itself… You must be quick to grab the molt soon after the tarantula has shed it’s skin or else the tarantula is likely to much on it. Bon appétit!
If the molt gets eaten you’ll have to wait until next time for the chance to revel it’s gender.
Not all tarantulas will much on their molt however, if the molt is recovered quickly after the tarantula has shed not only will the molt be soft and pliable (which makes the next step much, much easier) but you won’t give him/her the chance to eat it.
If you are able to get to the molt before it’s eaten be extremely careful not to disturb the soft and very vulnerable tarantula!
I have the intact molt, now what?
Is the molt soft? If not take care not to break it (the molt will crumble easily when completely dry) soften it in some warm soapy water for 15-90 minutes, or overnight. How long it needs to soak depends on how large and how dry it is. Make sure the molt is completely soft before proceding.
With the molt pliable, carefully unwrap the abdomen section. Examine the molt to look for the presence of a spermathecae. This female reproductive organ is where sperm is stored until the eggs are laid.
While a female can be identified by the confirming the presence of a spermathecae, a male can be identified by confirming the absence of a spermathecae.
The spermatheca is located between the first pair of book lungs.
Pictured below is a female Grammostola porteri (Rose Hair). The spermathecae is being manipulated with a toothpick.