Gyrinus

Gyrinus, commonly known as whirligig beetles, are a genus of aquatic insects belonging to the family Gyrinidae. These beetles are easily recognizable by their distinctive behavior of rapidly swimming in circles on the surface of freshwater bodies such as ponds, lakes, and slow-moving streams. They are gregarious insects, often found in large aggregations.

Whirligig beetles have a unique morphology adapted for their semi-aquatic lifestyle. Their bodies are streamlined and oval-shaped, typically measuring between 3 and 10 millimeters in length. A striking feature is their eyes, which are divided into two distinct parts: an upper portion that sees in the air and a lower portion that sees underwater. This adaptation allows them to simultaneously monitor both their aerial and aquatic environments for predators and prey. Their front legs are short and raptorial, used for grasping prey, while their middle and hind legs are flattened and oar-like, adapted for swimming.

Gyrinus beetles are predatory, feeding on small aquatic invertebrates, insect larvae, and dead insects found on the water's surface. They are also known to be scavengers. When disturbed, they can secrete a milky white substance from glands near their thorax, which is thought to be a defense mechanism to deter predators.

The life cycle of Gyrinus involves egg, larval, pupal, and adult stages. The larvae are also aquatic and predatory, possessing external gills. After completing their development underwater, they emerge from the water to pupate on emergent vegetation or other surfaces. The adult beetles then return to the water to begin their characteristic gyrating movements.