Prey Identification and Prey Localization in Surface-feeding Fish and Fishing Spiders

Surface-feeding fish and fishing spiders prey on terrestrial insects trapped at the water surface. In addition, semiaquatic spiders feed on small fish, frogs, and tadpoles (Gudger 1922). The stimuli involved are surface waves such as those generated by insects trapped at the water—air boundary or aquatic vertebrates contacting the water surface to feed or breath (Schwartz 1965, 1971; Bleckmann and Barth 1984; Bleckmann and Lotz 1987). Both surface-feeding fish and fishing spiders determine the direction and distance to a concentric wave source. They can do this even under open loop conditions (i.e., even if the wave generator is turned off before or at the moment the fish or spider starts to turn to the wave source) (Bleckmann and Schwartz 1982; Bleckmann and Barth 1984). In addition, these animals are faced with the problem of distinguishing between prey and nonprey stimuli. The present chapter does not attempt to review the pertinent literature on surface-dwelling animals (see Bleckmann 1985a and Chap. 25). Instead, it focuses on two questions; namely, how can surface-feeding fish and fishing spiders determine the source distance, and how can they distinguish between prey and nonprey wave stimuli?