Thursday, June 27, 2013

An observation of Leucauge venusta trichobothria and web eccentricities

Today I had a lovely opportunity to observe the peculiarities of Leucauge venusta. When I stepped outside my office for a breath of fresh air, I stumbled upon one specimen on top of a shrub at one corner of the parking lot, and another in the corner of a metal pole fence not thirty feet away.

When I looked at the second specimen, one detail leaped out at me: some delicate, feather-like structures on the front of the hindmost legs. A memory came back to me of seeing those particular structures on that particular species. Years ago, when I first took macro shots of Leucauge venusta, I noticed these structures only after examining the shots on a computer.

Today, though, the quality of the sunlight was just right, and the spider was perched just so. I could see the trichobothria easily with my naked eye, and no, I didn't know that word until I looked it up. I didn't have my camera with me, and I probably couldn't have gotten a decent shot of the trichobothria anyway, so I took the image below from The Find-A-Spider Guide for the Spiders of Southern Queensland after making sure I wasn't violating their image use policy. Isn't that a magnificent shot, and aren't the trichobothria beautiful? It's fascinating to be able to see filaments so delicate, and to know that the spider uses them to detect sound.

As I went back into the office, another aspect of my observation intrigued me. The first specimen--the one on the shrub--hung from the center of a neat orb web over a wispy tangle web, just as I'd expect from Leucauge venusta. But the second specimen, perched in a corner of a fence made of metal rods, had only a tangle web. To the best of my recollection, I've never before seen this species build a web that didn't include an orb.

It seemed obvious why the fence-dweller "chose" not to build an orb web; it would have been impossible to build in a corner. But were there other factors involved? For that matter, why did the spider select that site to build a web in the first place? Did it begin its climb "expecting" to find an opportunity to make an orb web and then, when it found none, "decide" to make what web it could rather than invest the energy required to climb down and find another site?

I see some research articles online that indicate variances in Leucauge venusta web placement and structure, but they seem only to deal with variances in orb webs as a function of sexual development. I haven't found any mention of the species building tangle webs without orb webs. So I'm posting this partly to share my gratification at having had the opportunity to make such a curious observation, and partly in hopes that some future Google search will lead someone who can answer my questions to this page.

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