Last Wednesday, I was so optimistic. I’d paired up Vera with a first-generation son of Gwyneth (GI-♂), they’d gone at it hot and heavy, and had produced an egg sac — an egg sac with a peculiarity I’ll get to in a moment. My plan was to go in today and open up the sac and see what embryos I’d find.
The peculiarity was that although I’d classified all my spiders as Parasteatoda tepidariorum, there was still a little uncertainty. The patterns of pigment on their cuticles were a bit ambiguous. Here’s part of the description of P. tepidariorum from Common Spiders of North America.
This is a medium-sized to large cobweb weaver. The abdomen appears teardrop shaped as the spider hangs updide down in its web, spinnerets uppermost. The cephalothorax is tan or brown. The abdomen color is extremely variable, usually shades of light brown with a mottled tan or brown. Some individuals are nearly black, others unmarked and pale. The legs are darker at the joints.
The egg cases of this spider are tan and tardrop-shaped, point uppermost.
This describes my spiders perfectly, given that there is variability in the patterning of the abdomen. They look different, which had me worried that I may have gathered a couple of different species, but then the description of the egg case settled it for me: Gwyneth had produced lovely tan, teardrop-shaped egg cases. Case closed, right? Gwyneth and her progeny were P. tepidariorum.
Then Vera produced an egg sac. Vera herself also fits that description of P. tepidariorum to a T.
But the egg sac she produced was a cottony, pure white ball. What? I flipped through my books looking for some indication of what this might mean, and found a description of Steatoda triangulosa, which is also common in this part of the country.
This is a medium-sized cobweb weaver. The cephalothorax is reddish brown. The legs are light brown with dark brown bands. The apdomen is light brown with two rows of angular spots or bands of dark reddish brown separated by white areas with a mottled appearance. In some individuals this pattern looks checkered.
The egg case is a fluffy white sphere.
Uh-oh. Are Vera and Gwyneth from two different genera? There’s nothing in Vera’s abdominal pattern that fits S. triangulosa, but maybe that’s highly variable in this species, too, and the egg case definitely fits this description. But she’d bred with P. tepidariorum! Were the new eggs hybrids? Was I just a terrible ignorant klutz playing the taxonomy game poorly? I went into the lab to take a few steps towards finding out.
And…disappointment. The “fluffy white sphere” was gone — it had been torn apart. The eggs within were dried up lumps. Uncertainty reigns.
I put the two lousy parents into a petri dish and made a video. You look and tell me: Parasteatoda tepidariorum or Steatoda triangulosa? Looking at just the adult morphology, I’m saying P. tepidariorum, but what do I know. Video below the fold, with an agitated pair of spiders scurrying about.
All I can do is move on. Vera is in a new vial all by her lonesome. I’ve bunked GI-♂ with a GI-♀ (that’s right, he’s with his sister committing incest, and yes he was inseminating her within minutes). But at least it’s not miscegenation!
I’ve also paired up another GI-♂ with a daughter of Xena, XI-♀. So I’ve got two pairs breeding right now. The females are young and on the small side, about half the size of Vera, so we’ll have to see if they’re old enough to reproduce.
Cross your fingers, or whatever superstition brings you a sense of satisfaction.