Immature Running Crab Spider

2013 August 24

I found this spider (which I think was not yet fully grown) wandering around on our house siding near the front door on June 30, 2012.

Even though it was wandering around as a free hunter rather than crouching in a web, I don’t think it was a wolf spider, because it just has eight beady little eyes rather than the two big eyes and six small ones that are characteristic of wolf spiders.

Originally, I thought this was an immature funnel-weaver, and was going to put it in a combined post with the male funnel-weaver I posted last week. But once I had pictures of both spiders together in one document, they were clearly not the same thing at all.

Looking at the eye pattern and carapace[1] shape, and doing the best I can with the keys in “Spiders of North America”, I think this is one of the Running Crab Spiders in the genus Philodromus. These are distinct from the “regular” crab spiders in that their second pair of legs is longer than their first pair[2], and they roam about to hunt rather than setting up ambushes. I also think it is an immature spider, because a mature female would have a bigger abdomen, and a mature male would have enlarged “boxing glove” pedipalps. The book says that the only reliable way to identify an immature spider to species is to raise it up to adulthood and re-examine, so this looks like where we stop.

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[1] The carapace is the back of the body segment that all of the legs come out of. This particular one has a carapace that is about as long as it is wide, while the funnel-weaver from last week has a carapace that is much longer than its width.

[2] Looking at the first picture, though, I notice that the second leg on the left is significantly longer than the second leg on the right. The spider may have lost the second leg on the right when it was younger, and it has been growing it back little by little on every molt since then. It might have gotten the new leg up almost to full length by the time it reached adulthood.

3 Responses leave one →
  1. August 24, 2013

    Running Crab is its Indian name. It’s English name is Thaddeus.

  2. Carole permalink
    August 24, 2013

    And, you’ve taught me to look at the eye pattern. Thanks!

  3. August 27, 2013

    Yes you are correct, it’s a “Running Crab Spider”. These spiders can easily be distinguished by the fact that there, second pair of legs are twice longer than the other legs.

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