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.

Steatoda grossa (aka the false widow)

Steatoda grossa female

Some time ago I found a spider in my kitchen that I identified as Steatoda grossa. For most people that means very little, but for me it was rather exciting as they are not considered common in Ohio, where I live. Identifying spiders isn’t as easy as looking at the abdominal patterns, which is what most amateurs do when looking through a field guide. The patterns on spiders can be variable. You must look at the genitalia for most spiders in order to conclusively identify them. For female spiders you must look at the epigynum, which is located on the ventral side of the spider’s abdomen near the epigastric furrow. Viewing this on larger females can be accomplished by placing the spider in a Ziploc bag, placing her so that she is ventral side up, and holding the bag tight enough to reduce movement without squishing her. I was able to do this with my Steatoda and was able to confirm that she was in fact Steatoda grossa. If you want to see an example of the epigynum diagram you can see one on Bugguide.

Steatoda grossa epigynum (viewed through a microscope)

 

Steatoda grossa are members of the Theridiidae family, commonly referred to as cob web weavers, due to the tangle web they weave (Adams and Manolis 2014). Worldwide there are more than 2,200 species of Theridiidae (Bradley et al. 2013). This family includes the Latrodectus (the widows); Steatodas superficially resemble Latrodectus, leading to the common name of “false widow” (Adams and Manolis 2014). Steatodas are not usually black, but as they are dark in color in low lighting they can appear black (Howell), and unlike the true widows, Steatodas lack the hourglass marking on the ventral side of the abdomen. They tend to hang inverted in their cobweb (Adams and Manolis 2014) which gives a clear view of the ventral side to determine that no hourglass is present. The females can live up to six years (Bradley et al. 2013). They are not considered harmful to people (Bradley et al. 2013) but in many ways provide us benefits as these spiders eat a lot of the things that we considered pest species. They like to live in and around our home, and I like to think of them as my personal pest control army.

Steatoda grossa male

 

A short time after I found the female in my kitchen I found a male Steatoda in my bathroom.  I was fairly confident that the male was also Steatoda grossa, but the trick with the Ziploc bag doesn’t work with males as it is the structures of the pedipalps that you need to see to determine species. I placed the male in a vial, and tried to photograph him at various angels to see if I could determine species. Although I didn’t get any images that confirmed 100% he was S. grossa, I felt that I could see enough of the structures to be confident enough to try introducing him to the female.

Steatoda grossa male and female. (Male web building (left), and mating (right)

 

On May 24^th, 2015 I decided to introduce the male to the female. This can be a stressful event as either one of the spiders can decide not to be friendly to the other, and you can end up with both spiders injured or dead from the ordeal. I was very nervous, but gently placed the male in the enclosure with the female. (It is better to introduce the male into the female’s enclosure so that he can get chemical signals from her web regarding her reproductive status.) There were a few tense moments when they approached each other, and then the male retreated to the bottom of the enclosure where he started spinning a small web. The best I can describe it was a platform that he suspended himself inverted beneath, about as big around as he was with his legs outstretched. He carefully attached lines to the webbing of the female. Once he was done he started tugging on the female’s web. I have heard that male spiders will use this to communicate with the female that he is of the same species and eager to mate. It didn’t take long for her to proceed to his location in the enclosure. There was some front leg tapping, and a couple of attempts to pull the female closer that ended with her retreating, but after a couple of tries he successfully wooed the female and mating ensued. I have posted a couple of videos documenting this, the courtship, failed attempt, and successful mating here, and a better view of the mating here.

The first Steatoda grossa egg sac.

Once the mating was complete I removed the male from the female’s enclosure. On June 6^th she created her first egg sac, and not long after that she created a second egg sac. I have been keeping her well fed, mainly on Isopodas, as they are easy to catch and she seems to enjoy them.

 

Steatoda grossa spiderlings with the second (yet to emerge) egg sac.

On July 7^th, 2015, I was thrilled to see that nearly fifty spiderlings have emerged from the first egg sac. They are still very small, and I personally think they are adorable. Now I just need to wait for the second egg sac to hatch, and then I can release them in and around my home, so that the next generation of pest control is in place.  For those of you interested I have since preserved the male in ethanol, and was able to get some decent photo of his palps, to be 100% certain that he is Steatoda grossa. He will be donated to the Ohio State University’s Museum of Biodiversity. I am looking forward to finding many more in and around my house!

Male Steatoda grossa pedipalp

 

 

 

Work Cited

Adams, Richard J., Manolis, Tim D.,. 2014. Field Guide to the Spiders of California and the Pacific Coast States. Berkeley, CA: University of California Press. .

Bradley, Richard Alan., Buchanan, Steve., American Arachnological Society.,. 2013. Common spiders of North America. Berkeley, CA: University of California Press.

Howell, W. Mike., Jenkins, Ronald L.,. 2004. Spiders of the Eastern United States : A Photographic Guide. Boston, MA: Pearson Education.