Elongated Running Crab Spider

2008 March 1

I’d like to say right now that, if you want to get pictures of all the bugs in your house, you really can’t beat having a 2-3 year old child helping you find them. Sam found this spider on the rug just a couple of weeks ago (in January)[*], and brought it to me alive and undamaged. It even has all of its legs for once!


This is a “Running Crab Spider”, of the “Elongated” type, genus Tibellus. They have a distinctive feature: they like to stretch out along brown grass stems and lurk about, like this one is doing on a bamboo skewer (it isn’t fully streched out, they can have their two front legs completely straight and flush with whatever they are hanging onto, but I couldn’t photograph it like that because it kept lifting up its front legs every time I took a picture).


For once, we can actually see the eyes clearly, because the eyes are dark while the body is light-colored. There are definitely eight equal-sized eyes, in two curved arcs of four each.


This is most likely Tibellus oblongus, a common species in North America, and evidently also in Europe[1]. The body shape and coloration are so close to an exact match that I can’t see any differences at all.

From the side views, it looks like the pedipalps are not enlarged at all, so I’d be inclined to think this is a female. Although, it’s also pretty slender, which could mean that it is a male, or might just mean that it is immature.



Its presence in the house is, I think, a bit unusual. I’m not finding anybody that mentions them as being part of the common house fauna, although this paper[2] lists Tibellus oblongus as one of a number of “winter-active spiders” that routinely rummage around in the space between the snow and the ground all winter, hunting springtails.

It was probably living outside under the snow[3], and got in through one of the numerous cracks in the foundation of the house[4]. It would be interesting to rig up something specifically to catch the little arthropods under the snow, maybe some sort of pitfall trap . . .

[*] Sam caught another one on Feb. 26. If we can find something smaller than cluster flies for it to eat, maybe we’ll raise it in a jar for a while (we already have a cobweb weaver and a European House Spider in jars, but they are both big enough to easily eat flies)

[1] For once, maybe Europe and Asia got an invasive species from us, and not the other way around. But then again, these are pretty northerly spiders, and so I suppose they could have just gone all the way around the polar regions when the Bering Land Bridge last formed.

[2] That paper is pretty interesting, it turns out that there is a lot more hunting action going on under the snow than one might normally think.

[3] The technical term for this is the “subnivean environment”, it is the gap where the warmth from the ground has melted away some of the snow, and the remaining snow is propped up a bit by dead grass and leaf litter. This leaves a few millimeters of just-barely-freezing conditions where cold-tolerant critters can move around and carry on their lives.

[4] There are some pretty substantial openings, some are evidently large enough to let snakes get in. At least, our cats periodically turn up with small garter snakes in the basement, and they are gettin in somehow. Ah, the joys of living in a drafty old farmhouse . . .

5 Responses
  1. March 1, 2008

    …but I couldn’t photograph it like that because it kept lifting up its front legs every time I took a picture).

    That’s because it was waving to you! “Cheeese!”

    I’m interested in the eight eyes. Do we know what or how spiders see with all those eyes? What advantages does that give them over having two? Increased depth perception to assist in lightning-fast attacks? Or do they perceive a wider radiation band then us?

  2. March 1, 2008

    There’s a nice writeup about spider vision at the Australian Museum Online site. The short answer is that most spiders don’t see very well, and their eyes are mainly just light/dark detectors with varying sensitivity to light. The benefit of the multiple eyes is apparently that they can see a wide field of view (remember that they can’t turn their heads or roll their eyes, so each of their eyes are permanently pointed in a specific direction).

  3. March 12, 2008

    How do you get these shots so close and clear? Any time I try to take photos of any insect they seem to want to run around at the most inconvenient times!

  4. March 12, 2008

    They run around a lot for me, too. It makes me crazy sometimes. Putting them in the refrigerator for a couple of hours first often puts them into a torpor, which gives a few minutes on the photographing stage where they hold still while they wake up. One thing that helps a lot is I have a glass petri dish to put them into, so when they warm up enough to start moving fast, they mostly end up running around the rim instead of fleeing. For really uncooperative ones, I put a piece of optically-flat glass over the top of the dish to keep them from getting out, although then I have to worry about glare off of the glass.
    As for the camera, I’ve got a pretty complete description of the whole cobbled-together photographing rig here

  5. sandy hance permalink
    August 26, 2013

    I just saw this spider yesterday and it had a black stripe down its back. it also jumped a foot in the air when I got close to it, was glad to see what it might be, thought it was a grass spider but this thing was as long as my hand and came from a cornfield or the yard. it ran so fast I lost it

Comments are closed.