A Basic Guide to Sexing

Sexing is best and most accurately done with a shed skin (Exuvium). There are other methods but these take more experience and do not seem as accurate for the sub adult spider. Adult males on the other hand are hard to mistake for anything other than male.

This is the sub adult exuvium of an immature male Brachypelma emilia.(Mexican Red Leg) The 4 white areas are the book lungs, and between the furthest set of lungs the area is smooth. Denoting a male.

This one is the sub adult exuvium of a Lasiodora parahybana. (Brazilian Salmon Pink) Here the space between the first set of lungs has a horny, paler coloured lip. That is the spermethecae, or sperm storage sack of the female tarantula.

This is an over simplified idea of sexing, as there are several shapes of spermethecae, dependent on species, but this at least gives you the right place to look. There are some species where the male may have very small organs in the same place as the females, and it takes years of experience to sex the harder species. A binocular microscope is an invaluable tool if you want to try to sex your own spiders.

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If you look at the picture on the left, you can see the ends of the palps are a different shape to the picture on the right. Both are of the same spider. These are now rounded. This is a newly moulted male and you can see the red area under the spider where the red hairs and now white soft fangs are. In a few days these will be back to normal. This species does not have tibial spurs which most species have when the male matures. The palps on the immature picture on the right look like the rest of the spiders feet.

There are people trained in sexing from a shed skin. There may be a nominal charge for the service.

Mature male Theraposa blondi

Immature picture of the same spider

Adult male tarantulas are generally very easy to identify. The main difference is noticable on the small set of "legs" at the front. These are called pedipalps, or palps. In the mature male the palps become  highly sophisticated secondary sexual organs. Often a male will look like he is wearing "boxing gloves". Also in most, but not all species, you will find a "finger" on the underside of the first set of front legs, these are called tibial spurs and are used in the act of mating, to hold the weight of the female at the difficult angle necessary for insertion of the palpal bulbs into the pouch of the female.

This is a fairly good picture of the pedipalps and tibial spurs of the male tarantula. If you look on the leg at the top of the picture, you can see a small protuberance on the underside, that is a tibial spur. This one is small, some are almost finger like. The picture also shows the "boxing glove" look of the mature palps.