Female Crab Spider

2008 April 5

Back in November, I posted pictures of a male crab spider, today we have some pictures of a female, for contrast. She probably isn’t exactly the same genus, but she’s fairly close.

femalecrabspideredf1reduced.jpg

She’s got pretty hairy legs for a crab spider. I originally thought she was in the genus Misumenops based on the hairy legs, but it is pointed out in a comment below that she has some traits that are more consistent with the genus Xysticus.

Incidentally, while it is usually possible to tell a crab spider by their shape and stance (laying flat, with elongated front legs held in front ready to snatch things), the way to *really* tell them from other spiders is their eyes. They are arranged like this:

femalecrabspidereyes.jpg

If you ever go through a spider identification key, the jargon that the arachnologists use for the eyes is:

AME (Anterior Median Eyes) – the two eyes in the front center
PME (Posterior Median Eyes) – the two eyes in the back center
ALE (Anterior Lateral Eyes) – the two front eyes that point to the sides
PLE (Posterior Lateral Eyes) – the two rear eyes that point to the sides.

Arachnologists like to use the sizes and shapes of the eyes for identifying spiders because that is something that tends to stay very similar between closely related spiders. It is evidently very easy for spiders to evolve different coloration patterns and even changes in their body shapes, but evolving a new eye distribution or resizing the eyes takes a lot more generations. So, the species in a given family will all tend to have the same eye pattern. The unfortunate part of this is that you really can’t make out the eyes without magnification, and sometimes not even with magnification. So, for a quick ID of a spider that is rapidly scurrying behind the refrigerator, the eye pattern doesn’t really help much.

Anyway, the crab spiders all have this fairly characteristic arrangement of eyes: two sweeping curves running around the front of the face, with all the eyes about the same size and pretty much equally spaced along the curves.

femalecrabspideronstage.jpg

As for how they hunt, spiders in this genus typically hang out in flowers and wait for some pollinator to come by. Then, as David Brady so eloquently put it, they bite it in the face. This unfortunately means that crab spiders aren’t as beneficial to us as other spiders, because instead of mostly eating pest species, they eat pollinators. Luckily, they don’t really get plentiful enough to make a serious dent in the pollinator population, so our crops still get pollinated. There’s no real need to worry about crab spiders.

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This spider is still from last summer, but it is probably the last of my “backlog” bugs that I’ll be posting for a while. Why? Because the spring flush of insects is on! We found a bunch of “winter stoneflies” yesterday (they were being stalked by tiny spiders), and there are caterpillars coming out of hibernation and new insects in the house that haven’t been seen all winter. Time to get cracking, these bugs won’t photograph themselves!

2 Responses
  1. Stephanie C permalink
    October 9, 2008

    I like your pictures!
    I may be mistaken, but it seems to me that this female belongs to the genus Xysticus, not Misumenops. Members of Misumenops have their lateral eyes on large tubercles whereas members of Xysticus have lateral eyes on small discrete tubercles, as in your pictures. It also seems to me that Misumenops would have longer legs I and II than the specimen in your pictures. The tan/brown pattern on the abdomen also fits Xysticus.

  2. October 10, 2008

    You may very well be correct, I have changed the post to include the possibility that it is Xysticus. Thanks!

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