At the end of the school day yesterday (4 PM) I found one of my large Mexican redknee tarantula juveniles (Brachypelma smithi) laying on its back with all eight legs spread apart. I’ve seen this enough now that I readily recognize it as the start of the final phase of the molting process.
I’ve observed the duration of each successive molt increases. It makes sense – the more tarantula there is, the more molting that needs to occur. The evening’s events unfolded in a way that allowed me to drop by school shortly after 9 PM to check on the success of the molt.
As I expected, I encountered the newly eclosed individual on its back, s l o w l y moving all eight legs, which had just recently emerged from the old exoskeleton. Its newly eclosed drying abdomen lay on top of its former abdomen, in a shallow pool of exuvial fluid, the liquid mixture that allows the developing new exoskeleton to separate from the old exoskeleton that housed it only a few hours earlier.
The newly emerged tarantula rolled slightly to its side, allowing me to remove the old exoskeleton in it entirety. Or so I thought. I typically try to manipulate the legs and body parts back to their original positions so that my students can readily see the old exoskeleton proportions. This also allows me to photograph the newly emerged individual next to its former exoskeleton.
The moist exoskeleton’s legs and body regions readily moved back to their original positions, though the dorsal regions of the cephalothorax and abdomen separated from the original exoskeleton prior to my manipulations.
The result? I now had in front of me an exoskeleton that looked just like the ones that others exhaustingly prepare for gender determination. (See Sexing a tarantula tutorial 1. Other videos in the series can be accessed by clicking on titles to the right of the video on the YouTube page.)
Everything I needed – camera with macro lens and extension tube, a fast computer with a quick Internet connection and an array of dissecting microscopes and lights – were already in my lab. A new adventure began.
According to Michael Jacobi (tarantulas.com), “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 or exoskeleton). 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, which is the sperm storage receptacle of the female.”
He continues with “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.”
Quick manipulation of the abdomen using two dissection pins, combined with a rapid succession of photographs while the exoskeleton was still quite moist, led to the photograph below.
Enlargement of my digital image made clear the similarities between this individual and those pictured in the high quality images accessible at http://www.tarantulas.com/sexing.html, http://www.arachnofreaks.com/forum/forum_posts.asp?TID=188, http://giantspiders.com/sex_determination.html, and http://milehighbugclub.com/Methods%20for%20Sexing%20Tarantulas.htm .
Nonetheless, I sought confirmation regarding the gender of this individual from several experienced tarantula keepers/breeders. Thanks to Joe Mastous, Dale Wooley, Paul Lawinczak and Jamie Lessee for confirming my first gender identification!
This tarantula’s sibling is in pre-molt and has predictably molted within twelve days of the first tarantula’s molt. Perhaps the timing of the sibling’s molt will allow me to practice again!