Curling behavior in a pteronarcid stonefly nymph

The research described in this thesis examined the question of curling in pteronarcid stonefly nymphs. Two major hypotheses were identified: (1) that curling functions as an anti-predator behavior, and (2) that curling functions as a position behavior, enabling nymphs to control their location while drifting in the stream current. Experimental methods varied with hypothesis tested. Curling's function as a position behavior was primarily tested in the laboratory in a series of experiments examining how nymph behavior changed with experimental variable. Curling's function as an anti-predator behavior was tested in a series of predator-prey experiments in which the reaction of several fish predators to curled and uncurled (open) nymphs was recorded. Laboratory research was supported by field observations. Results from the experiments examining curling's function as a position behavior showed that small (younger) nymphs curled more frequently than large (older) nymphs. Curled nymphs were also shown to sink more rapidly than open nymphs. Results from the experiments examining curling's function as an anti-predator behavior indicated that some fish predators did reject nymphs, that nymphs always curled when attacked by fish, and that surviving, curled nymphs sustained fewer injuries than surviving, open nymphs when attacked, but rejected, by fish. Wide variation in fish behavior, both between species and within species, made interpretation of these results difficult. From these results it was concluded that curling may function as both a position behavior and an anti-predator behavior.