The most accurate method of determining the gender of a live tarantula is to examine the interior of the abdominal portion of its exuvium (molted skin)*. A female tarantula sheds the spermathecae lining along with the rest of her exoskeleton and an experienced examiner can look for the presence of spermathecae. This usually requires the use of a stereo dissecting microscope with lighting above and below the stage, but spermathecae are visible to the naked eye with most skins of large adult tarantulas. Examining exuvia (molts) for the presence or absence of spermathecae requires experience, softening the skin, and carefully unfolding and untwisting the abdominal skin so that the four book lungs and the genital opening are stetched flat. Spermathecae lie above the genital opening [epigynum] between the anterior book lungs. The spermathecae are surrounded by the uterus externus. In some species, the males have accessory organs that can be mistaken for spermathecae by inexperienced examiners and carefully looking for the uterus externus is important.

Since accurate sexing by this method requires a great deal of experience and a good microscope it is best for most tarantula keepers to save their molts and send them to someone like myself who will examine them at no cost. I accept skins that are 2 inches in legspan or greater and email the results at my earliest convenience.

There is a means of determining gender by examining the external features a live tarantula. A male tarantula has additional spinnerets [fusillae] along the epigastric furrow that are connected to silk-producing epiandrous glands. It is believed that these auxiliary organs are used in sperm web production. For more information on this "epiandrous fusillae" method of sexing tarantulas click here.

Directions

• place just a few drops of rubbing alcohol into a vial, film canister or ziploc bag - do not wet skin
• label the vial, canister or bag with scientific name and any number or name you use for identification in your collection
• carefully remove the exuvium from the cage using forceps
• ensure that the molt is complete [missing legs are fine] and is at least 2" in legspan
• gently place the exuvium in the labeled vial or bag
• double bag one or more containers of exuvia
• pack in a small box that will protect during shipping - padded envelopes can be used for molts in film canisters, but not those in baggies or brittle plastic vials
• place a note in the box including your name and email addy
• send package to: Michael Jacobi [my sexing service is temporarily suspended, my apologies for the inconvenience]

Terms

My sexing service is provided free of charge to anyone. Since I donate my time to do this I hope you will understand certain policies I have implemented regarding examining exuvia. First, I do this at my convenience as time permits and your patience is expected. Please do not email to inquire whether your molts have been received or examined unless you mailed them at least several weeks earlier. Also, if contacting me becomes necessary please do so via email, not phone. Second, results are sent only via email. Please do not request that I call you. If you have limited email access you may enclose a self-addressed stamped envelope and I will mail the results. Finally, with very few exceptions, exuvia are discarded, not returned. If you wish to have the skins returned to you must ask me prior to sending the molts — a self-addressed return envelope or package with plenty of postage will be required. Many skins become damaged when they are manipulated during examination and having them returned is not recommended.