An air puff stimulus evoked the swimming of an intact cricket, Gryllus bimaculatus, placed on a water surface. When only the forelegs were intact, swimming was initiated frequently, but flying was never initiated. On the other hand, flying was initiated when only the middle legs or hindlegs were intact. Therefore, the sensory inputs from the forelegs are important in the initiation of swimming and for the inhibition of flying when on the water surface. After bilateral ablation of the middle legs and hindlegs, the bilateral segments of the remaining forelegs were sequentially ablated from the distal area to the proximal area of the legs. After bilateral ablation of all tarsomeres, the relative occurrence of swimming decreased and that of flying increased. After the following ablation of the bilateral tibiae, most insects responded to an air puff stimulus by flying. Experiments performed after coating the leg surface with enamel resulted in almost the same behavioral change as that observed in the ablation experiments. These results suggest that the sensory receptors responsible for the initiation of swimming and the inhibition of flying are mainly located on the surface of the tibia and the tarsus of the forelegs. The behavioral change between swimming and walking was also studied using methylcellulose solutions of various viscosities. On the methylcellulose solution, the relative occurrence of walking in the crickets increased with an increase in the viscosity of the solution.