Transmission of natural and arteficial vibrations in webs of Nephila clavipes was examined using laser Doppler vibrometry to determine how this spider discriminates and localizes stimuli. 1. Vibration signals of four entrapped insect species peaked at different frequencies from 5--30 Hz, but their spectra overlapped considerably. Peak amplitudes spanned 50dB. 2. Transmission of longitudinal vibrations along individual radii was attenuated over ca. 12cm by 4.0 + 2.7 dB; attenuation values 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 thread transmission increased by 2.2-5.8 dB after cutting the connecting auxiliary spirals, demonstrating that vibrations "leak" from stimulated radii via these threads. Auxiliary spirals provide structural support to Nephila webs at the expense of degraded directional transmission. 4. Upon single-point stimulation, vibrations measured around the web hub and at the spider's tarsi revealed 2-D vibration amplitude "gradients" of 20-30 dB indicating the stimulus direction. In contrast, measured vibration propagation velocities of 70-1500m/s resulted in time-of-arrival differences at the spiders tarsi of < 1.5 ms, which may be too brief for stimulus direction determination.

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Dragline use by an orb web spider (Nephila clavipes) was analysed by observing both intact spiders and those prevented from producing a dragline. The behaviours observed were those associated with returning to the web hub and prey capture. Upon returning to the hub, spiders resume the resting position by rotating within the hub, producing several new dragline attachment points during the rotation. The importance of the spider's use of the dragline was made clear by preventing experimental animals from producing the dragline. During resting, the permanent dragline-to-web attachment enabled the spider to maintain the correct posture. Prey capture behaviour was adversely affected in spiders prevented from using the dragline: without a dragline, all relevant components of the behaviour required more time to perform, and movements within the web (e.g. toward prey and back toward the hub) were directed less accurately. The bene®t of the dragline to the spider, in terms of safety, time, energy and reduced exposure to predators, is likely to be signi®cant.