Sydney Sue's Gender Identity Crisis

MONDAY, JUNE 27, 2016   |   POSTED BY MICAH GARTMAN

Remember the time I told you Sydney Sue is a girl? Well, it turns out I was very, very wrong. Brace yourself: Sydney Sue is, in fact, a boy. How did I make such an obvious mistake, you ask? As I recently learned, determining a tarantula's gender is a complex matter. Allow me to explain…

Spiders do not have external "private parts." (Actually, mature males develop secondary sex organs called emboli on the ends of their pedipalps. We'll get to that in a moment.) Instead, their primary sex organs are on the inside of their body. The only accurate way to differentiate a boy from a girl is to look at their molted skin under a microscope—which essentially allows us to see "inside" the spider. That's where this story begins.

On March 17, 2016, Sydney Sue started fasting, signaling an impending molt. And on April 6, 2016, Sydney Sue molted—an astonishing 330 days after his previous molt. He grew so much after molting that he ran out of space in his house! Here he is one week after molting:

Sydney Sue was in no harm being in such tight quarters. Tarantulas prefer small, confined spaces and will spend most of their life in an underground burrow, a hole in a tree trunk or in a hammock made of silk suspended from a branch. Being out in the open would leave the tarantula at risk of being eaten by an eagle or coyote. Here is a wild Lasiodora sp. Theraphosinae, warm and cozy inside a fallen tree:

While making preparations to move Sydney to his new house, I decided to take a look at his molt under my new microscope. What I saw—or, more accurately, didn't see—surprised me. "Where are her 'girl' parts? They're not here?!?!" This is Sydney's latest molt:

The light tan-ish colored area within the circle is where Sydney's sex organs are located. If he were a "she" we would see the spermatheca (pronounced sper-muh-THEE-cuh). This is the organ where the male tarantula inserts his emboli (pronounced EM-bowl-ee) and deposits his sperm. Here is the spermatheca of a Grammostola grossa, the Pampas Tawney Red tarantula:

When a male tarantula reaches sexual maturity—called the ultimate molt—he makes a special web called a sperm web. As you might expect, he puts his sperm on the web, then uses his newly-formed emboli to scoop it up and store it for later use. The emboli are attached to his pedipalps (pronounced PED-ee-palps), which are the first pair of appendages on a spider's body. All spiders—male and female—have pedipalps, which look like a pair of short legs. During the act of mating, the male will repeatedly insert his emboli into the female's spermetheca and deposit his sperm. Tarantula mating is quite a site to behold. Here is an embolus of an Avicularia versicolor, the Antilles Pinktoe tarantula:

As tarantulas began to evolve 250 million years ago, each species developed its own unique spermatheca with a size and shape dramatically different from every other species. Furthermore, the male's emboli are designed to only fit into the spermatheca of the female from his own species. It's not known why this happened, but it's obvious that Mother Nature did not want tarantulas to breed across species—or even within their own genus. As of today, there are 969 known species of tarantulas. Here are only a few variations of spermethecae:

While plowing through Google reading everything I could about tarantula's private parts, I came across the name of the world's foremost expert on sexing spiders. His name is Dr. Fred Sherberger, and he provides his gender identification services free of charge to the tarantula hobbyist community. I sent him an email asking if he would take a look at Sydney's molt and he happily agreed. So I packed up the molt and dropped it in the mailbox. A week later, Dr. Sherberger sent me this image taken from his microscope:

Dr. Sherberger's finding: It's a boy!!!

(I also sent him a link to this site. He replied, "I like the Sydney Sue.")

So what does this finding mean for Sydney Sue in the long term? He will continue to eat, sleep and dig holes, molting on a regular basis. In another six or seven years, he will undergo his ultimate molt, bringing him into sexual maturity. He'll make his sperm web and prepare to venture off in search of a mate. Since there are no suitable ladies to be found in the wilds of West Houston, I will attempt to find a human with a mature female Grammostola pulchripes. With any luck we will be able to breed them and hopefully they'll make lots of babies. Then, within a year or so after maturing, he will slowly die of old age :(

Until then, Sydney Sue is free to roam around in his spacious new man cave. He moved in on May 13, 2016, with little fanfare. He slowly crawled out of his old house and onto my hand, then proceeded to walk up my arm. Once he finished his little journey, we put him in his new home and he took a nice, long nap.

Sydney's new "suit" perfectly camouflages him with his new surroundings. It's always a challenge trying to find him—you never know where he's going to be. Can you find him in this picture? If not, put your cursor over the photo for a clue:

As you can see, he has adapted well to his new home. He acclimated within a day—as opposed to his last move when he pouted for over a week. During the day he sits on top of his cork bark house, looking over his domain and enjoying the A/C. He still loves for his room to be cool and dark with the ceiling fan on low. He's not the least bit spoiled ;)

Have a great summer! Be nice to spiders!

Spiders need love, too.
IUCN and CITES classify 37 species of tarantula as threatened or critically endangered.
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