Mechanics of trichobothria in orb-weaving spiders (Agelenidae, Araneae)
- Cite this article as:
- Reißland, A. & Görner, P. J. Comp. Physiol. (1978) 123: 59. doi:10.1007/BF00657344
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When a fly is humming at a distance of about one centimetre from an orb-weaving spider (Agelenidae) the trichobothria on the spider's extremities are deflected by air streams and air vibrations. Frequency analysis of the hum of the two prey animals,Drosophila andMusca, shows that the effective sound velocities of the harmonics with frequencies inferior to some five hundred Hz exceeds that of higher frequencies by a factor of at least 5. Biologically relevant resonances would, therefore, have to be looked for in the range of a few hundred Hz. Frequency response diagrams show that single hairs have no resonance between a few Hz and approximately 2 kHz. The maximal relative amplitude of hairs of different lengths shifts from the longer to the shorter hairs with increasing frequency. As this is only a minor effect, however, it appears that there is no frequency discrimination by the mechanical apparatus. Constant air streams with a velocity of 40 mm/s cause hair deflection of about 10 degrees (the hair's bend is neglibible). Similarly, near-field particle velocity of sound fields up to a few hundred Hz is well transmitted. The mechanical directional sensitivity does not depend on the azimuthal angle of deflection. Thus, information about direction and velocity of stationary and near-field air movements is transmitted without deformation by the mechanical apparatus. This is well matched with the fact that the hair is multiply innervated.