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Unformatted text preview: J. Exp. Biol. (1965), 43, 185-192 185 With 1 plate and 9 text-figures Printed in Great Britain THE SIGNAL GENERATED BY AN INSECT IN A SPIDER'S WEB BY D. A. PARRY Zoological Laboratory, University of Cambridge (Received 29 January 1965) INTRODUCTION It is generally accepted that web-spinning spiders detect and find prey in their webs through the mechanical signal generated by the prey. There is also a good deal of evidence that spiders discriminate between different types of signal. Barrows (1915) caused Epeira sclopetaria to orientate, or move, towards a tuning fork; and found the frequency-band of 24-300 cyc./sec. most effective. Meyer (1928) obtained responses from several species of Agriopidae (orb-web spinners) to a tuning-fork (435 cyc./sec). Peters (1931), with Epeira diademata, found that the spiders did not respond to a dead fly placed gently in its web; if, however, the fly arrived in the web with a jerk or if, once in the web, it was suddenly tapped with a needle or stimulated with vibrating forceps, then the spider responded. Liesenfeld (1956) also found, with Zygiella x-notata, that a vibrator suddenly switched on would produce a response, while, if the amplitude of vibration was slowly raised, no response occurred. Walcott & Van der Kloot (1959) obtained responses in Achaearanea (= TheridionV) tepidariorum to a vibrating phonograph needle over the range 400-700 cyc./sec., while between 700 and 3000 cyc./sec. the spider retreated or dropped from the web. Tretzel (1961) similarly obtained responses from Coelotes terrestris to sinusoidal vibrations generated by a loudspeaker movement and drew attention to the ability of females to distinguish between prey and their own young. Most recently Bays (1962) has conditioned Araneus diadematus to discriminate between tuning forks vibrating at 262 cyc./sec. (= c) and 523 cyc./sec. (= c'). In contrast to the amount of work on the response of spiders to sinusoidal and other artificial signals, there is little information about the natural signal generated by living prey. Liesenfeld (1956) analysed cinematograph records of flies moving in the web of Zygiella and recognized wing vibration, body movement and the resonance of the insect in the web as components of the movement pattern. Tretzel (1961, see above) tape-recorded signals from the web of Coelotes produced by prey and by young spiders, and compared their frequency content. He found that the signals produced by prey contained higher frequencies, and showed a greater range of intensities, than those produced by young spiders. But he doubted whether the spider's evident ability to discriminate between prey and young did in fact depend on frequency. Walcott (1963) published spectral analyses of recorded signals produced by bees and flies in the web of Achaearanea but found the energy distributed over a wide frequency range (mostly within 100-5000 cyc./sec.) Thus we have evidence that various spiders discriminate between sinusoidal signals The signal generated by an insect in a spider's web...
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