Steatoda Cobweb Weavers

2013 December 14

I found these nearly-black spiders on August 11, 2012, nder the hatch leading to the old basement (although I could have found them there at any time, they always seem to be around in there). The first one is a male.

You can tell he’s a male from his big, boxing-glove-like pedipalps. I’ve sometimes seen these spiders being accused of being “black widows” by people who’ve never seen an actual black widow. But they clearly aren’t, as they are more of a very, very dark burgundy than a true black, and have light-colored underbellies.

Here’s a closer look at his pedipalps, from below this time:

The females are somewhat bigger, mainly in the abdomen, and have thin pedipalps, but otherwise look pretty similar.

The underside of the female is supposed to be useful for species identification, so here it is.

The female looks to have three openings on her underside: the gonopore is the one closest to the legs, the spinnerettes are closest to the abdomen tip, and I think the one in the middle is her anus.

For comparison, here’s a male abdomen. He seems to be lacking the full gonopore opening, although it does look like he might have a structure there to secrete sperm that he can transfer to his pedipalps.

So anyway, the shots of their undersides show enough detail that I think these are Steatoda borealis, a native northern species. They are known for living under bark and stones, in rock crevices, on bridges, and in outbuildings and unfinished basements. Well, what do you know? That’s exactly where I found these!

3 Responses
  1. December 14, 2013

    I’ve always thought that cobweb spiders were the trashy slobs of the arachnid world.

  2. Carole permalink
    December 14, 2013

    Interesting. Need to look up gonopore. that’s a new term.

  3. Judy permalink
    December 23, 2016

    Years later, your post came in very handy! I’m in Western New York, and have my mother’s car (along with my mother) up from Maryland for a few months. Today I needed to get something out of the hatch, and when I closed it, I discovered a spider on the outside of the hatch. It’s been below freezing for days, although now it’s just barely over it. Our garage isn’t heated, and while it doesn’t get as cold as outside, it definitely ain’t warm. Anyway, we love spiders, so I gently encouraged her to walk on to my hand, and I took her down to our plant room where I start seeds and keep my more tropical plants in the winter. She instantly perked up and quickly made herself at home on a pineapple top. My concern, though, was, what kind of spider is this? I have a car coming from warmer climes, I also have received packages from South Africa in the last few days, and, well, it could have come from anywhere. I was able to rule out anything potentially dangerous (we have a child and a senior citizen with us) and happily rule IN what she is, a Steatoda borealis, which makes perfect sense up where I am. I’m glad to have her as a guest this winter, and I’m glad to have found your post – thank you!

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