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Determining the gender of a tarantula

Is it male or female?

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.

The same molt (Female G. porteri) approx. 5 1/2″ DLS. The spermathecae is highlighted in red (below)

The spermathecae will often vary in size and shape depending on the age and species. Aside from using the spermathecae to determine gender this reproductive organ is often used to identify and distinguish certain species.Below is the molt of a 3-4″ female B. cabocla (Brazilian Red Head)Here is the same B. cabocla molt, a little closer, with the spermathecae outlined in yellow:

Now compare these females molts to that of a male Avicularia (Pinktoe) below.

Notice it’s completely flat between the first set of book lungs? There is no flap/presence of a spermatheca confirming this male. Male Avicularia (Pink Toe) approx. 3 1/2″ DLS Has no spermathecae.

The Looking Methods

So, you don’t have an intact molt handy? Be advised the looking methods are not very reliable, can not be used on spiderlings and small juveniles as the smaller specimens look more or less the same (at least to me…)

The exception to this rule is mature males as once a male has reached his mature (also known as “final” or “ultimate” molt) he can be easily identified and his gender 100% confirmed by the presence of his male reproductive organs.

You can use the looking method to visually sex the actual tarantula two ways, by ventral sexing, that is looking at the tarantulas ventral side, the underside of it’s abdomen or by dorsal sexing, this is looking at the tarantulas dorsal or back/top side.

Ventral comes from latin venter meaning belly, stomach or womb. Dorsal form the latin dorsum meaning back and/or ridge of a hill.

We do not use the looking methods to determine gender here at Jamie’s Tarantulas with the only exception of “suspect, not guaranteed males” offered every-so-often. Although the looking methods are not considered to be completely accurate the topic still be covered in depth as to help others to make educated guesses as to the gender of their specimen, at least until an intact molt/exuviae can be recovered.

Ventral Sexing It is possible to make an educated guess at the specimens gender by examining the ventral side of the abdomen. You’ll want to try this with tarantulas minimum about 2″ DLS Ventral sexing is not considered an accurate way to determine gender however, most often the specimens intact molt is not immediately available and we must rely on what we have and accept the answer will only be a “best guess”

Some advice for those wanting to ventral sex: Getting good at ventral sexing is something that comes with experience. No one starts off good at it, In my early hobby days can recall going crazy because I couldn’t detect any difference. I can tell you the more you practice, the better you’ll get! Look at lots of tarantula undersides. It will become easier and easier!

Here is an Aphonopelma chalcodes (Arizona Blonde) 4 1/2″ male first unedited:

Second, we have added a yellow pencil line to show the more flat angle 5-7 degrees between the first pair of book lungs:

Third, we have added another yellow pencil line to show the “triangle” or “arch” around the area of the epiandrous fusillae, only present in males

Here is an Aphonopelma chalcodes (Arizona Blonde) 5″ female first unedited:

Second, we have added a yellow pencil line to show the larger angle of 15-20 degrees between the first pair of book lungs. Notice there is no “triangle” or “arch”?

Originally I took photos of Brachypelma emilia for this ventral sexing article however, their black undersides did not make for good, clear photos. I then choose the lighter-colored Aphonopelma chalcodes (Arizona Blonde).I must warn sexing from photos can be difficult to impossible. Personally, it’s hard for me to look at something 2D representing a 3D image. Sometimes the lighting can play tricks on us, and lightening photos can sometimes reinforce sometime that was never really there.This article is using photos of an adult and sub-adult lighter-colored species, the absolute best I could find for this job from my vast collection. These photos I personally took and was very careful about selecting for this article, I wanted to make sure they easialy and accurately showed the visual differences between the two genders.Keep in mind that typically the smaller/younger the specimen the specimen is, the more subtle the differences. The darker the color, the harder it typically is for me to make a good ventral best guess.Determining gender from a photo is very difficult and even those (such as myself) with some experience ventral sexing will likely have much more difficulty sexing from a photo vs being there, looking at the tarantula. We appreciate if those refer to this and other resources online for general sexing, and to try to get eyes on your own spider(s) to gain the experience to get better at sexing. I recall in my early hobby days it was so difficult but with time and practice it gets easier to make an “educated guess.” Don’t get discouraged and stick with it. You will get better with time and experience!

Here are some easy-to-spot visual characteristics between mature males and mature females

…that don’t require looking at their underside.

When a male matures (has his final or “ultimate” molt) he gains some distinguishing characteristics such as “tibial hooks” (present in most species) and bulbous pedipalps which are often referred to as “boxing gloves”

Mature Male C. cyaneopubescens (Green Bottle Blue) “Boxing gloves” are circled left & tibial hooks are circled right Also notice the lankier overall appearance, including longer legs and smaller, more narrow fangs of the mature male…

Mature Male C. cyaneopubescens (Green Bottle Blue) below:

Mature Female C. cyaneopubescens (Green Bottle Blue) pictured below:

What about this photo? Of these two B. hamorii/smithi (Mexican Red Knee) can you tell which one is the mature male and which one is the female?

The male can identified (top) by the presence of his “boxing gloves”. One of his tibial hooks is just barely visible (as a cream colored lump) on the right side near where they’re “holding hands”. Just like the GBB notice the males lankier overall appearance, including longer legs and smaller, more narrow fangs when compared to the mature female (bottom)Here is the same photo again, with the males “boxing gloves” and his visible tibial hook circled in yellow:

Dorsal sexing immature specimens:

Larger juvenile and sub-adult specimens can sometimes be identified by their “body type.” Just like the adult male GBB and B. hamorii/smiti adults pictured above immature males typically have a lankier overall appearance including longer legs and smaller, more narrow fangs when compared to the females same size DLS. Be aware that females of most species go though a leggy adolescent phase and can be sometimes be mistaken for males during their “awkward teenage” years. Occasionally I might see an unusually stocky immature male.

We hope you found this article useful!


For those looking to purchase from Jamie’s Tarantulas:

If the gender of the specimen is known it will be included in the title.

If the gender is unknown no gender will be stated and the specimen will be sold as “un-sexed”.

Those tarantulas are sold as “unsexed” because we are unable to determine, or even guess their gender at this time.

We do not attempt to “pick out” females or males from the “unsexed” specimens.

Your chance of getting a male/female is roughly 50/50 with an “unsexed” specimen.

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