VISUAL CONTROL OF CURSORIAL PREY PURSUIT BY TIGER BEETLES (CICINDELIDAE)

Target detection poses problems for moving animals, such as tiger beet les, that track targets visually. The pursuer's movements degrade targ et image contrast and induce reafferent image movement that confounds continuous detection of prey. In nature, beetles pursue prey discontin uously with several iterations of stop-and-go running. The beetle's dy namics were analyzed by filming pursuits of prey or experimenter-contr olled dummies. Durations of stops are inversely related to prey visual angular velocity; as the prey image moves between neighboring ommatid ial fields, the beetle relocalizes it and renews running. During subse quent runs, translation and rotation depend upon prey visual angular v elocity and position, respectively, seen during the previous stop. The beetle runs, then stops, while prey continues moving. After two to th ree iterations of stop-and-go the beetle catches its prey, suggesting open-loop control of running. Computational model simulations produce good qualitative spatio-temporal fit with actual pursuits. However, wh en pursuing prey dummies, beetles track continuously and quickly follo w changes in target position, suggesting closed-loop control using a p osition-sensitive servo mechanism. Differences between these types of pursuit control system are discussed with respect to limitations in si gnal detection, particularly spatio-temporal contrast, that may force beetles to use an open-loop system.