1. Polyphemus chases were video-recorded in a laboratory tank, and the positions and orientations of the chaser and target were digitized at 100-ms intervals.
2. Analysis of the resulting track reveals three main phases: chaser pauses, shadowing prey at a constant distance, and rapid leaps onto prey. Chases do not all end in contact — they are sometimes terminated by the chaser peeling off.
3. Pauses are triggered by rapid image expansions, and persist for as long as the image continues to expand.
4. The shadowing phase includes intermittent sudden forward movements, which could provide visual information about the absolute size of the prey, using a triangulation method. Chasers are successful in avoiding contact with very large and very small prey.
- © 1988 by Company of Biologists