Cobweb spiders

2008 January 26

This is a species of spider that has successfully colonized the dark corners of our house: so far S_ found me three specimens to photograph in December and January (two females and a male). I could tell that one of them was male because he had enormously swollen pedipalps, which I understand means he was ready to mate. He was within a few inches of one of the females, so we suspect that he was courting her when he was caught.


I was trying to get a good idea of the size and arrangement of the eyes, because that’s one of the features that is useful for identifying them, but man, are they hard to make out. In this face shot, I can only really see a few of the eyes, but from the way the ones I can see are spaced it looks like there are eight eyes arranged in two horizontal rows of four each.


You can see on the females that their pedipalps are much smaller than the male. In this shot, you can also see the first female’s “chelicerae”, which are her mouthparts. They are closed at the moment, they open sideways to expose a pair of fangs that unfold kind of like a pocket knife.


These are pretty cold-tolerant spiders, they weren’t slowed down much by refrigeration. In fact, they went ahead and spun webs right there in the jar. Very minimalist webs, mainly just a bunch of apparently random strands, and they would hang pretty much in the middle of them, like this:


This next one is the second female, you can see that she has a much bigger abdomen than the male does[1]. She also has a pattern of “dimples” on her abdomen that he didn’t have.


Based on the kind of web that they made, I figured that they were probably some sort of cobweb weaver, possibly in the genus Steatoda. I actually posted some of these pictures on BugGuide in hopes that somebody might be able to confirm this, but I only got one response from a person who said it looked like a Steatoda hespera. This is a possibility, I suppose, but it doesn’t really look quite right and it would be nice if some expert could confirm it. It probably won’t happen, though, since positive species ID of spiders usually needs a microscope and a view of the underside of the female.

Anyway, since we’re finding them in the middle of the winter, it is safe to say that they are part of our house fauna and not just incidental visitors from outside. In addition to these relatively clear shots, I have pictures of what are probably two more[2][3] that we spotted last spring: one because it was busy working on killing and eating a centipede about five times its size:


and one that had somehow caught a tick:


They certainly have ambition, I’ll grant them that. In particular, eating a large centipede like that was probably pretty risky, considering that centipedes are also carnivorous. The tick was probably no danger to the spider, but the web it was in was about 5 feet from the floor, and it is unusual that a tick would have crawled up so high.

[1] These pictures are using a different grid than usual. Sam had been playing with my photography dish, and the 1 mm graph paper circle got lost. So, these are photographed on the only other graph paper I could find at the moment, which had a 0.2 inch grid (about 5 mm)

[2] It’s a little hard to be sure if they are the same species, because the pictures from last spring came out a bit blurry, but they are certainly consistent with being the same species. I don’t think anybody can prove that they aren’t.

[3] I think I actually already posted a picture of a male of this species, back almost a year ago. At the time, I thought it was a mesh-weaving spider, but now I’m not so sure.

6 Responses
  1. January 26, 2008

    The picture of the spider killing a centipede is pretty cool. I’m wondering how often that technique is successful – my understanding is that centipedes can be pretty nasty (to insects their own size, anyway). Pretty cool for the spider that can take it on and win.

  2. January 26, 2008

    It’s too bad the spider vs. centipede came out so blurry. This was actually one of the first spider pictures I took, and I was still having trouble getting the macro mode to work right at the time. I did get a very short video of it, which is actually a bit clearer.

  3. February 3, 2008

    These look to me like the common American house spider, Achearanea tepidariorum. I have a series on my blog on these: I’ve been watching one particular spider for a full summer, and now am keeping an eye on her egg cases.

    You can see my blog posts and photos here, or on Flickr.

    And yes, these spiders are quite able to take on prey twice and more their size. My “Fat Momma” regularly grabbed big moths and crane flies.

  4. February 4, 2008

    Nice pictures of your spiders in action! Thanks for the pointer, they certainly do look like, if not the same species, at least a closely related one.

  5. August 26, 2012

    I am particularly interested in the one with the dimples, could someone tell me if a smallish wolf/funnel web weaver could take on one.

  6. August 27, 2012

    Anonymous: I expect that the answer to most “which spider would win?” questions is “whose web are they on?” If they both meet in the cobweb-weaver’s web, then the wolf or funnel web weaver is probably doomed because it will get tangled up in the random, sticky strands that it can’t hold onto properly, and the cobweb weaver will have them for lunch. But if they meet in the funnel-weaver’s web (or, for the wolf spider, out in the open), then the cobweb weaver probably doesn’t stand much of a chance, because then the cobweb-weaver can’t use its normal means of getting around (swinging quickly between individual web strands). Spider webs are a tremendous advantage to the spider that inhabits them, and a spider out of its web is often practically helpless.

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