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The long and short of 'web legs.' (study of webs made by spiders with regenerated legs)

The long and short of "web legs'

For those not intimidated by a spider web, its airy complexitycan be a thing of beauty--and a marvel of engineering. Among the different silken traps built by spiders is the commonplace, mostly circular web of the garden spider, which weaves spiral strands on supports slung between plants or buildings. Included in that process is construction of the initial auxiliary spiral used for support and later removed, and of the final main, or capture, spiral. From camera-carrying scientists intent on web research came the suggestion years ago that some of the eight legs on a spider are used as measuring sticks to control the distance between strands as they are spun into place. But what happens if the web-gauging appendages aren't their usual long, leggy selves?

Whether lost in battle or through the natural process ofmolting, missing legs of garden spiders usually are replaced, but the new legs are shorter than the originals. Using computers to analyze photographs of different webs, Fritz Vollrath from Oxford University in England studied what happens to webs made by spiders with regenerated legs. As he reports in the July 16 NATURE, Vollrath collected spiders that had regenerated one or more of their legs on one side of the body. He then studied the geometry of the webs they made, finding that shorter first legs (or second, if the first was missing) resulted in narrower spacing between strands in the capture spiral. However, even if all four legs on a side were shorter, the strand spacing in the auxiliary spiral was unaffected. Among other experiments by Vollrath are those showing that rotating a web-building spider in the vertical plane results in "dramatically deranged' capture spirals but normal auxiliary spirals. These observations, says Vollrath, show that different "behavioral rules' determine the pattern of the different spirals built by garden spiders.
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Publication:Science News
Date:Aug 1, 1987
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