ORIENTATION TO VIBRATIONS IN SAND BY THE NOCTURNAL SCORPION PARUROCTONUS-MESAENSIS - MECHANISM OF TARGET LOCALIZATION

Paruroctonus mesaensis accurately determines the direction and distance of a local source of substrate vibrations in sand. This scorpion has two types of vibration-sensitive mechanoreceptors on its tarsal leg segments and one of these receptors, the basitarsal compound slit sensillum (BCSS), appears to mediate the information used to determine vibration source direction. 1. The tarsal leg segments contact the substrate at eight points in a circular array (Fig. 2). All eight of the BCSS on these segments are used to determine direction of a wave source, not just those closest to the source (Fig. 3). When some of these sensors were eliminated, the response to local disturbances of the substrate was biased toward the direction of the remaining receptors. 2. The time delay between arrival of a substrate-borne signal at the BCSS is the most important cue for determining direction of a distant signal source (Fig. 4). The scorpion can detect time delays as small as 0.2ms but is maximally sensitive to 0.8 to 1 ms delays. The conduction time of surface waves in sand from tarsi nearest the source to tarsi farthest away is about 1 ms. 3. A mechanism for target localization is proposed where target direction is determined by the temporal pattern of activation of the slit sensilla, and target distance by the spatial pattern of stimulation of tarsal mechanosensory hairs. © 1979 Springer-Verlag.