VIBRATIONS IN THE ORB WEB OF THE SPIDER NEPHILA-CLAVIPES - CUES FOR DISCRIMINATION AND ORIENTATION

Transmission of natural and arteficial vibrations in webs of Nephila c lavipes was examined using laser Doppler vibrometry to determine how t his spider discriminates and localizes stimuli. 1. Vibration signals o f four entrapped insect species peaked at different frequencies from 5 -30 Hz, but their spectra overlapped considerably. Peak amplitudes spa nned 50 dB. 2. Transmission of longitudinal vibrations along individua l radii was attenuated over ca. 12 cm by 4.0+/-2.7 dB; attenuation val ues for transverse and lateral vibrations were 22.2+/-4.6 dB and 26.2/-4.3 dB, respectively. Some transmission spectra characteristics may be explained by ''resonances'' of the spider and threads. 3. Radial th read transmission increased by 2.2-5.8 dB after cutting the connecting auxiliary spirals, demonstrating that vibrations ''leak'' from stimul ated radii via these threads. Auxiliary spirals provide structural sup port to Nephila webs at the expense of degraded directional transmissi on. 4. Upon single-point stimulation. vibrations measured around the w eb hub and at the spiders tarsi revealed 2-D vibration amplitude ''gra dients'' of 20-30 dB indicating the stimulus direction. In contrast, m easured vibration propagation velocities of 70-1500 m/s resulted in ti me-of-arrival differences at the spiders tarsi of <1.5 ms. which may b e too brief for stimulus direction determination.