Single male spider seeking mature female. Must have pitted carapace, be between 6 and 7 mm, and have white “T” marking on the front of the abdomen. Likes to hang out, do ropes courses, and enjoys romantic insect dinners at twilight.
I was visiting family in the Jefferson Hills area south of Pittsburgh over the winter holiday in December. In the corner, where the white wall met the white ceiling, a black spider with huge palps stood out like a piece of coal in the snow. Palps are the short, leg-like appendages near the face of the spider. If the palps are swollen, like boxing gloves, the spider is male. The huge palps and his other unique spider characteristics, helped me ID him as Steatoda borealis. Steatoda is a genus in the Theridiidae family (comb-footed or cobweb spiders). There are nineteen different kinds of Steatoda spiders found in North America and the borealis species is common around Western Pennsylvania, yet, this guy seemed to be all alone in that giant continent of a house wandering for a mate. Not any ordinary spider female would do…he was looking for the right type, a Steatoda borealis lady!
On a mild January day at Round Hill Park near Elizabeth, PA, I caught a small (5mm), blackish cobweb spider and guessed her as Steatoda borealis. Richard Bradley’s Spiders of North America lists them as 6-7mm for adults She was immature and not ready to start dating. Aside from that fact, she had all of the qualities of a fine, female S. borealis with her pitted carapace, and light “T” mark on the front of her abdomen. I fed her well hoping to prompt her to molt into maturity. I also hoped the male wouldn’t keel over of old age before I could introduce them!
February came, about a week past Valentine’s Day. Lady borealis had molted into a mature female with a shiny, oval abdomen of purplish brown, lightly banded, tan legs, and measured a petite 6.25mm. Since it’s the males who travel looking for stationary females, I thought her house would be an appropriate meeting place. Her “house” consisted of a curled piece of paper towel roll which she draped indiscriminately with silk, a characteristic of all cobweb weavers. Her cobweb spread out around the house attaching to the lid and sides of a reused live cricket container measuring 4.5 x 4.5 inches. During the day, or when disturbed, she would hide in the paper towel roll. On quiet nights, she’d hang on her porch waiting for food delivery.
I dropped the male into her container. Lady borealis was in her house. He landed in one corner, a good bit away from the house and didn’t move. I started on something else thinking he would need to acclimate and cautiously announce his presence, like any polite spider would do. This could take awhile. I checked in about thirty minutes later and he was IN her house! The female seemed to be cool with it – she had her legs pulled close and sat motionless while the male walked in circles just millimeters away, adding his own silk to her web. I thought this might be moving a little too fast… he was already decorating! The male seemed to be confident turning his “back” to her. She could’ve attacked, but didn’t. Apparently, she liked him! This went on for almost forty minutes. Every few minutes, the male looked like he was stumbling. Since it was a repetitive motion, I thought it might be intentional. I dug for some info about this and found out there are stridulating organs on the front of S. borealis abdomens which they rub against their carapace to make noise. The silk “decorating” behavior has also been documented in a few scientific papers (see below) and is part of this spider’s mating ritual. Both males and females have stidulating organs. He was decorating and making lovely spider music to lull his lady! It must have been the Borealis Exclusive mix because it was inaudible to me. Finally, he approached her face to face with front legs tapping hers. She tapped back and then all of the stars aligned – they mated! An hour later, I called it a night leaving the two alone. It is interesting that these spiders are usually very shy darting into a retreat at the slightest bump. While they were mating, they were oblivious to my intrusions as I documented, photographed, and yes, filmed.
The next morning they were both hanging out in the house. Female spiders don’t eat the males as often as you think, but it can happen. Later in the day, the male was outside of the retreat so I gave him a lift back to his own container where he lived as a bachelor for only two more weeks. During that time, Lady borealis became gravid and a small, cottonball-like egg sac appeared in her house hanging like a chandelier. Male borealis was successful and his wait was not in vain!
The spiderlings emerged in April and not long after that, a second egg sac appeared. From this ONE successful date, there could be close to one HUNDRED Steatoda borealis babies! Thankfully, human dating does not end up this way.
Lady borealis does little to care for the young. She has free-range kids whom are allowed to come and go as they please. In fact, she even ditched them during a late photo shoot for this blog! She used her dragline to seemingly catapult out of the vial I was using. I felt something light hit my hand and she disappeared! I could not find her! I even called the cats in for backup. I gave up and figured since she was a cobweb weaver and cobweb weavers usually stay in one place, eventually, I’d find her. And I did two days later. She moved into a gap under the desk leg and was sitting outside on her porch waiting for food delivery. I put her in a new container where she has the whole place to herself. The kids have already moved out to the backyard, on their own into the big, wide world of the compost pile.
Although the hero of the story died, there is still a happy ending. He did find the mature female was looking for. I’m sure at least one of his spiderlings will live to perpetuate his original post in the spider personals. The Steatoda borealis romance continues here in Western Pennsylvania!
Bradley, Richard. Common Spiders of North America. University of California Press, 2013.
Dondale and Redner, Evidence for displacement of a North American spider, Steatoda borealis (Hentz), by the European species S. bipunctata (Linnaeus) (Araneae: Theridiidae) Canadian Journal of Zoology, Vol. 64 #
Lee, R.C.P. / Nyffeler, M. / Krelina, E., 1986, Acoustic communication in two spider species of the genus Steatoda (Araneae, Theridiidae)
Levi, Herbert, 1957, The spider genera Crustulina and Steatoda in North America, Central America, and West Indies. Bulletin of the Museum of Comparative Zoology, Vol 117, No. 3
Ubick, Paquin, Cushing and Roth. Spiders of North America – an identification manual, 2nd ed. American Arachnological Society, 2017.