Nature Note – Whirligig Beetles

Watermelon seeds on the water? Nope they're whirligigs! Photo by flickr.

Late summer is the time to see this year’s crop of whirligig beetles, those watermelon seed sized insects that spin and spin on the water surface. The beetles congregate atop tranquil waters around docks or near shore vegetation. The whirligigs that emerge this time of year are newly hatched from eggs laid in the spring. They will overwinter in mud or debris. You can notice two different sizes of the beetles, representing different genera. If you capture and squeeze one of the large ones, they emit a green apple smell, apparently the smaller ones smell worse. The smell is a predator deterrent. In labs, large mouth bass forced to eat whirligigs will spit them out and then re-ingest them in an attempt to dilute the chemical. Whirligigs use their antennae to detect waves on the water’s surface. They then navigate toward the motion hoping to find a struggling insect they can eat. They will also scavenge dead insects from the water surface. You can attract the beetles by repeatedly dipping your finger into the water to create waves. In addition to spinning on the surface, the beetles can dive for prey or fly off to other waters.