Structural analysts can identify vibration modes, and often locate defective structural elements, by measuring vibrational responses while applying a driving signal to the strudture under examination. This is referred to as system identification (SI). When you lightly disturb the webs of spiders of particular species (e.g., daddy longlegs) you will see the spider pumping his body to shake the web, sometimes by a reciprocating motion and sometimes by whirling in circular motion. He invariably finds a resonant frequency and his oscillations can become pretty large. Could he be employing SI to detect the presence of, and possibly locate, a prey insect? Web sites I have seen state that the shaking serves either to further entrap the prey, or as a form of camouflage for the spider itself. Could SI also be a reason? Detection/location by SI could be useful at night or if the spider's eyesight isn't very clear.
2007-07-12
02:52:12
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4 answers
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asked by
kirchwey
7