How to Sex a Tarantula (Without Losing Your Mind)
One of the most common questions I get is: “Is my tarantula a boy or a girl?”
Short answer: you usually can’t tell just by looking at them in the enclosure. The most reliable way is by checking the moult (shed skin).
There are some ventral (underside) clues on live spiders, but they’re easy to get wrong and depend a lot on species, size, and experience. So in this post I’m focusing on the moult method, because it’s the gold standard for most hobbyists.
Why the Moult Method Works
When a female tarantula matures, she develops a set of reproductive organs called the spermathecae inside the moult, right behind the book lungs. Males don’t have this structure.
So in simple terms:
- Female moult = a little flap / pouch / “U” or “V” shaped structure inside the exoskeleton
- Male moult = flat skin, no obvious flap or pouch
Once you know what you’re looking for, it’s actually pretty satisfying.
What You’ll Need
- A fresh moult (ideally within a day or two of being shed)
- Good lighting
- Tweezers or a small paintbrush
- A bit of water
- Optional but helpful: a magnifying glass or your phone camera zoom
Step-By-Step: Sexing From a Moult
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Wait for the moult to dry a bit
Let it firm up so it doesn’t turn to mush when you handle it, but not so dry that it’s crispy and brittle. -
Find the underside of the abdomen
You’re looking for the skin that used to cover the belly of the tarantula, between and just in front of the back pair of book lungs. -
Gently soften the area
Lightly mist or dampen the abdominal skin with water. This helps you unfold it without tearing. -
Carefully open the abdomen
Use tweezers or a small brush to tease it open. You want that area to lay as flat as possible. -
Look at the epigastric area
This is the section between the top pair of book lungs on the underside.
Female: you should see a noticeable flap, fold, or pouch – that’s the spermathecae. It can look like a tiny set of lips, a “V,” or a thicker raised area depending on the species.
Male: the area is smooth and flat, with no distinct flap. -
Take a photo and zoom in
If you’re unsure, snap a clear pic with your phone and zoom in. Sometimes the difference jumps out once you’re not squinting over the table.
Ventral Sexing (Why I Don’t Rely on It)
You’ll see people online talking about sexing tarantulas by looking at the underside of a live spider (the epigastric furrow, the shape of the epiandrous fusillae, etc.).
That can work:
- on larger juveniles/sub-adults,
- with certain species,
- and with practice.
But for most keepers, especially newer ones, it’s very easy to mis-sex an animal this way. If you’re selling or planning breeding projects, moult sexing is the responsible option.
Common Reasons You Can’t Tell Yet
If you can’t see anything clearly, that doesn’t always mean “male”. It could be:
- The tarantula is still too small – early moults can be hard to read.
- The moult is too damaged – the abdomen may have torn right where you need to look.
- The moult is too dry and brittle – it rips when you try to open it.
In those cases, don’t stress it. Just wait for the next moult and try again.
Quick Summary
- The most reliable way to sex a tarantula is by checking the moult, not just eyeballing the spider.
- Look on the underside of the abdomen, between the first pair of book lungs.
- Female: visible flap / pouch (spermathecae).
- Male: flat, no flap.
If you’re ever unsure, keep the moult, take a clear photo, and ask other keepers for a second opinion. We’ve all stared at a fuzzy little flap wondering if we’re seeing things.