Steatoda grossa: The continuing saga.

Female Steatoda grossa (The momma)

As you may recall I posted about my Steatoda grossa on July 9^th, 2015.

Steatoda grossa (Female offspring from first egg sac)

Steatoda grossa (male offspring from first egg sac)

Steatoda grossa female with egg sac #9

 

She was mated on May 24^th, 2015, and since that time she has produced a number of egg sacs, and hundreds of offspring. On March 3^rd, 2016 I was amazed to see her produce her ninth egg sac. She has been captive for over a year, and she has only had one encounter with a male when mating occurred. (Although there have been times when her offspring have stayed in the enclosure with her, none of them have reached maturity before they were released.) When sperm is delivered to a female spider it is coiled and encased in a proteinaceous sheath (Vöcking, Uhl and Michalik 2013) and it is known that the sperm is stored in the female in an “inactive” state, and is only activated when the female starts laying her eggs (Foelix 2011). It was shown that for Latrodectus hasselti (Redback Spiders) one mating encounter (even with a single insertion event) was enough to fertilize the females eggs for her lifetime (Andrade and Banta 2002) which could be years long. So although it is not ground breaking news it still caught me a little off guard that 284 days after she was originally mated that she was able to produce a viable egg sac.

Steatoda grossa egg sac number 9. (Left under white light, and right under UV light)

An interesting note: One day I was using a UV flashlight to look at some other specimens, and for no specific reason I decided to expose several of my captive spiders to UV light to see if I saw anything interesting. When I illuminated the Steatoda gross enclosure I noticed that there were particles in the developing egg sac that were highly reflective under the UV light. I had some of her hatched egg sacs and placed one under my microscope. I took pictures with regular white light, and with UV (black) light. Sorry that the picture quality isn’t better, but I only have a small hand held UV flashlight, and it isn’t very bright. As you can see there are particles in the old egg sac that are also very reflective of UV light. These appear to be the chorion of the old eggs. Chorion is the outer covering of the individual eggs (Foelix 2011), similar to the egg shell on a chicken egg. This egg shell is cast off and the larval spider remains in the egg sac while they continue to develop (Foelix 2011). This implied to me that at this point the eggs had hatched, and now I was just waiting for them to be mature enough to emerge from the egg sac.

Steatoda grossa hatched egg sac under white light (left) and UV (right)

On April 16^th, 2016, I was pleased to find that the spiderlings had emerged from their egg sac, and approximately 50 young spiders now share the enclosure with the female. Although I haven’t counted every individual I would estimate that each egg sac has contained at least 50 offspring. As this was her 9^th successful egg sac I would estimate she has produced at least 450 offspring! Having baby spiders emerge is always an exciting event, and I had been checking the enclosure regularly anticipating their arrival.

Steatoda grossa spiderlings from egg sac 9.

 

Steatoda grossa starting to construct an egg sac

On April 11^th, a little after 2:30pm, when I popped in to see if there were young spiders yet, I saw the female acting in an odd manner. At first I thought she might be tickling the egg sac, but soon realized that she was trimming her silk in an area of the web near the egg sac, creating an opening. The only reason I could think of that she would need an open area in the middle of the web for was to place another egg sac. I grabbed my camera and sat patiently photographing and taking video (which you can watch here) of the ensuing events. Once she had a clear area she started to lay down a pad of dense silk. This silk seemed to take tremendous effort to spin, and several times during the process she would pause. It wasn’t long before the dense silk was clearly visible, and I knew that egg sac number 10 was under construction.

Steatoda grossa laying eggs

She worked spinning the egg sac covering for about an hour and, when she shifted position, I had the honor of watching her lay her eggs. That step in the process only took minutes, and then she was back to spinning the silk covering to protect her young. By 5:30pm the egg sac was complete and she rested off to the side of her creation. She appeared shriveled up due to the loss in mass from her abdomen, but regained her figure by the next morning. So now the countdown in on for the next emergence of young, which I will be eagerly anticipating! (So for those of you keeping track this egg sac was laid 323 days after mating!)

Steatoda grossa putting the final touches on her egg sac

Andrade, Maydianne CB, and Erin M. Banta. “Value of male remating and functional sterility in redback spiders.” Animal Behaviour 63.5 (2002): 857-870.

Foelix, Rainer F.,. 2011. Biology of spiders. Oxford; Toronto: Oxford University Press.

Vöcking, Oliver, Gabriele Uhl, and Peter Michalik. “Sperm dynamics in spiders (Araneae): ultrastructural analysis of the sperm activation process in the Garden Spider Argiope bruennichi (Scopoli, 1772).” PloS one 8.9 (2013): e72660.