Tarantula Sex Identification

How to sex your tarantula

There are two ways to sex your tarantula— ventral sexing (external view) and molt sexing (internal view). Generally speaking, ventral sexing is a lot less accurate than molt sexing due to the fallibility of the human eye and camera, as well as confusion on how to properly ventrally sex a specimen. Both types look for signs of one sex: ventral sexing looks for signs of a male, whereas molt sexing looks for signs of a female. An absence of male characteristics— or absence of female characteristics, in the case of molt sexing, is what we use to confirm male or female, respectively.

Ventral Sexing

In ventral sexing, we look for signs of the epiandrous fusillae, specialized glands that only male tarantulas have and use when depositing sperm onto a sperm web.
In juveniles and spiderlings, this is not as developed, but can still be seen.
In subadults and adults, it is a lot more obvious as it manifests as a concentrated patch of hairs between the top set of booklungs.
This is generally a semicircle shape, curve-side up, on the tarantula’s ventral side. This patch is not necessarily darker in color, but it is different enough to where there is a discernible shape, even in juvenile specimens.
However, this shape is not necessarily particularly large, and depends on species and specimen age as to how obvious it is. In females, this is where their epigastric furrow is— there will be no epiandrous fusillae to see here, and will appear more uniform throughout.

Molt Sexing

In molt sexing, we look for the spermathecae, which is the organ that exists in female tarantulas to store sperm.
Similar to ventral sexing, these signs are not as obvious in younger specimens. However, microscopic analysis of even a spiderling’s molt can sex a tarantula by molt, if you know how to spot them developing.
The spermathecae vary in shape and structure from species to species, ranging from appearing as small curves to distinct horn-like structures. Males do not have spermathecae, and subsequently, a male tarantula’s molt will have no internal structures of this sort and appear flat in contrast.
The uniqueness of each species’ spermathecae shape is as unique as the shape of the male’s pedipalps, as the two fit with one another like a lock and key during the mating process. The spermathecae are generally very obvious in adult females, as they are fully developed structure with a clear, symmetric form.

Note: The shape of epiandrous fusillae can be seen with molt sexing, but it’s easier to simply look for the more obvious female internal anatomy versus imprints of male external anatomy.

Link to sexing guide image -Archived from birdspiders.ch

Tarantula Dan’s how to guide for sexing molts

Thank you to @spidertacular on Discord for this guide!