Diving of whirligig beetles: a novel method for transitioning from near-surface to underwater locomotion

Primarily water surface-dwelling whirligig beetles (Gyrinidae) dive to a full submergence when threatened by aerial predators. Their morphology and thrust generation mechanism adapted for their neustonic life (living on the water surface) suggests that there are no means for vertical momentum generation. Despite this limitation, they display rapid diving behavior saving themselves from the threat from above. Here, we present the mechanism behind whirligig beetle’s fast diving. The result of our in vivo experiments on their diving suggests their rapid transition from surface to underwater is initiated by bending their abdomen downward. The new body conformation generates additional drag on the abdomen, which torques the body in a favorable orientation for diving.