1. Giant water bugs swim when suspended free of the substrate. This situation contrasts with that of terrestrial insects which fly when freely suspended. Swimming can be stopped by returning contact to the bugs.2. Suspended bugs respond to wind with a general increase in rate and duration of swimming, followed by a decrease in both.3. When bugs are in water, swimming is stimulated by a hair bed located on the trochanter at the coxo-trochanteral joint. These hair beds seem to be stimulated by cuticular folds which cover them when the legs hang down, but roll back and heave them uncovered when the legs float, resulting in swimming.4. Flight or wing opening occurred with 8 of 44 suspended bugs. A hair bed on the head functions in both the maintenance and initiation of flight in response to wind.5. The bugs possess an elaborate pre-flight behavior which is apparently necessary to unlock a ball and socket mechanism attaching the wings to the pterothorax. This pre-flight behavior inhibits swimming and causes th...