Family: Gyrinidae
Subfamily: Gyrininae
Length: 9-16 mm
The Whirligig Beetles have not been adequately studied in West Virginia. Downie and Arnett (1996) reported no West Virginia records for any member of this family.
Two genera are found in this part of North America; they are Gyrinus and Dineutes. Gyrinus species measure 8 mm or under, and have a visible scutellum. Dineutes, pictured here, measures 9 mm or more and the scutellum is not visible.
One interesting trait of all Whirligig Beetles is that each of their two eyes is divided into two separated parts, one above the water line and one below the water line, for a total of four apparent eyes.
A laboratory study by Romney and Rossman (1995) found that Whirligig Beetles in the genus Dineutes tended to mass together when they were relatively well-fed, and that the beetles dispersed considerably when they were hungrier. Presumably massing together offers some advantage as defense from predators, but feeding is more successful when the beetles are not competing so directly for the same tiny arthropods.
Left: Whirligig Beetles may be found in large masses on the surface of lakes, ponds, rivers, and creeks. The common and Latin names refer to this beetle's practice of swimming quickly in small but erratic circles.
Right: Dineutes beetles at home on the Elk River.
