Excerpts from Jim Conrad's
from the April 22, 2012 Newsletter issued from the woods of the Loess Hill Region a few miles east of Natchez, Mississippi, USA
Whirligigs are those shiny, black beetles that skate across the water's surface at uncanny speeds, often suddenly swimming in tight circles. In a shallow, house-sized pond at the Refuge at about midday I came upon thousands of them floating in a car-tire-sized mass. My appearance at the pond spooked several Red-eared Turtles into splashing into the water, which made the mass break up. You can see them reforming below:
An artsy picture showing them snugly back together is at the top of this page.
Floating whirligig masses are called rafts, and the rafts may contain more than one whirligig species. A 1980 study by Heinrich and Vogt in the journal Behavioral Ecology and Sociobiology point out that whirligigs, when they're threatened, are equipped with "defensive secretions" that are so noxious that if an uninformed fish attacks one, it'll not attack a second time. Possibly when large numbers of whirligigs raft they produce such a "stink" that predators stay away.