Male cobweb-weaving spider

2007 April 28

The spider below had made a minimalist mesh-style web on the frame of our back door, so I took a bunch of pictures in-place with the improvised macro lens. By bracing against the surface of the door and taking lots of pictures, I managed to get a few that showed decent detail, but it was a lot of effort. Keep in mind that this is a little guy, only about 5 millimeters long. If there had not been a surface to brace against, there is no way I could have held the camera still enough to get an unblurred photograph.
But, not to worry! We have so much forgotten junk in the lab, there must be something that can be used to hold a camera steady, right?

Right! I would like you to meet “The Beast”, about 10 pounds of the finest brass machining the 19th century had to offer![1]
I found this old microscope frame stuck away in the back of a cabinet, along with a bunch of other microscope parts that were probably scrapped out sometime before I was born. This one was obviously the stage and mount for a dissecting scope, the mount is a nice 3-dimension positioner, moving up/down/forward/back/left/right with several inches of travel in each direction. With a bit of adaptation (mainly just getting a 1/4-20 capscrew to mount the camera, and drilling one hole so that the screw would fit), the camera and macro lens mounted up just fine.

So, how well does this work? I went back to the door, and the same spider was still hanging out a day later, so I coaxed him onto a piece of paper and got him onto the stage for a photo shoot:
The answer is, quite well! It was trivial to get it in focus, and the frame was so rigid that it easily stayed focused while I took the photo. The images were sharp enough that I could even zoom in on the head for a closeup.
Again, keep in mind that the spider’s *legs* were not much bigger in diameter than a cat’s whisker, the fuzz on the spider’s pedipalps (the boxing-glove-like appendages on either side of the mouth) is ludicrously fine. All in all, I’m very pleased with this apparatus.

So, given all that photographing, what is this little spider, anyway? It appears to be a member of the family Dictynidae,[2] which are small “mesh-weaving” spiders. More specifically, it is a male, because they are the ones that have the red bodies and the huge pedipalps. The females are kind of grey, nondescript spiders. This is another one of those spider families where you need to dissect the genitalia to figure out the genus and species, so a family-level ID is probably as good as I’m going to get. Especially since, immediately after his photo shoot, the little guy scurried off behind the stove and vanished.[3]

[1]I really have no idea how old this microscope frame might be, but judging from appearances, it might very well have been part of one of the first microscopes that the university bought when it was founded back in the 1880s. The optics have gone off to where the wild geese go, but hey, I don’t need them anyway. And there’s no fear that anyone will want this thing, the last person who would even in theory have remembered about the existence of it retired over a decade ago (and with the continuing crunch on for lab space, I would have had to throw it out in the next lab-cleaning binge anyway).

[2] Well, it is now almost a year later, and I’ve found a number of other spiders that appear to be the same genus as this one. I’m currently leaning away from the Dictynidae, and more towards some sort of cobweb-weaver, family Theridiidae. Possibly something in the genus Steatoda. Man, spider ID from photographs is hard!

[3] So more years have passed (it is now 2013), I’ve learned a lot more about spiders in the meanwhile, and I am now convinced that this is one of the Steatoda cobweb-weavers. Mesh-weaving spiders don’t enter into it. We may have some somewhere, but this one isn’t one of them.

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