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Spider Web Capture Thread
Argiope luzona
15.456, 119.922
Field Notes
Description:
Spider webs are, obviously, an extremely important element in the science of arachnology and there have been many scientific papers published on various aspects of web construction. One of these papers recently caught my attention - https://www.researchgate.net/publication/232679040... It was written by a group of French scientists who were checking the accuracy of mathematical formulae used in determining the Capture Thread Length of Orb-Weaver Spiders. Their purpose was to provide a formula which could be easily used by arachnologists in the field, enabling them to calculate the size of a spider web’s “Capture Area” (and, therefore, estimate the cost in energy to the spider). Apparently, the sticky silk thread of the capture area is the most “costly,” to the spider. It is absolutely fascinating stuff and it gave me the idea for this spotting. When I have been out on overnight spider observations, I have had the privilege of seeing Argiope luzona spiders sitting motionlessly, for hours, and then suddenly erupting into a non-stop, machine-like burst of activity, laying down the sticky silk thread in a spiral, on the radials of their webs. In the case of A. luzona (I don’t know about other spiders), the Capture area takes around an hour, or slightly more, to complete. Since witnessing these amazing bursts of energy from spiders, I have often tried to convey, to others, the sense of awe that I experienced, but it is difficult to engender much interest in a tiny creature performing a task in an area the size of a dinner plate. In 1954, when Roger Bannister was the first man in the world to run a mile (round an athletic track) in under four minutes, it was celebrated all over the world. When a tiny spider greatly exceeds that achievement, every night of its life, it doesn’t create much excitement. So, I have thought “What if I could “scale up” the creation of the Capture Area spiral, to human size. Would that make it more interesting?” Please see Notes below.
Habitat:
This spider web was spotted in our backyard. It was moored on two plants; a Painted Nettle (Plectranthus scutellarioides) locally called Mayana and a Miracle fruit (Crescentia cujete) called Kalabas in the Philippines. Plant information from stuartxchange.org.
Notes:
Using both of the methods employed in the scientific paper (and working with the photograph) – (1). I measured the entire Capture Thread Length using a divider compass (the scientists used an electronic caliper) and (2). I measured only the shortest and the longest laps of the Capture Thread, added them together and divided the total by 2, giving me the average length of a lap. I then multiplied the average length by the number of laps. Both methods produced the same result – the length of the sticky silk Capture Thread was 22,680 mm. At this point, I no longer followed the steps taken by the authors of the paper because they went on to develop several ways of arriving quickly, easily and accurately at the size of the Capture Area. For my purpose, I only needed to know the Capture Thread Length. Now that I had the length, my only remaining problem was scaling it up to human size and the simplest way was as follows: I measured the spider. It was 8 mm. (body length, excluding legs). Then I divided the Capture Thread Length by 8. The result was 2,835. Now I had a new unit of measurement which I called a “Spider Length”. So, the Capture Thread Length could now be considered to be 2,835 spider lengths. In order to “scale up” to human size, I measured my own body (excluding legs) and found it to be 900 mm. When this is divided by the size of the spider i.e. 900 ÷ 8 = 112.5. Therefore, I am 112.5 times the size of the spider. Now all I had to do was multiply the Capture Thread Length by 112.5 and the result is 318.9 metres. So, what’s all the fuss. A human can walk that distance in a few minutes. However, we have to bear in mind that the spider stops for a fraction of a second at each radial and sticks down the Capture Thread with a spot of “glue”. So, to draw a fair comparison, how about we give the human 320 metres of string, a pot of glue and a paintbrush so that he can stop at every radial and glue the string to each one. Then he would really be creating a spider web capture area. Now it might take him a bit longer to carry out the task. There are 52 radials supporting the Capture Thread in the web in my photo (and the Capture Thread makes 42 laps. So, the human would have to stop, bend down and glue the string 42 X 52 = 2,184 times. I think that would slow things down a bit. I know that some might not like this “childish” way of “scaling up” the spider’s work to human size, but I think that it really demonstrates the enormity of the spider’s task which it carries out, almost every night of its life.
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