AUGUST
1992

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

8-27-92

Whirligig Beetles Aptly Named

No insect is more appropriately named than an aquatic insect called the whirligig beetle. It is a common insect, found on the surface of the water in lakes and streams, where it swims in endless circles or semicircles. This swimming pattern has earned the insect a host of common names including the luckybug, submarine chaser, or writes-my-name beetle. Even its scientific family name — Gyrinidae — reflects its swimming behavior.

This insect could appropriately be called old four eyes. Not because it wears glasses, but because it has two sets of eyes. One set is on the top of its head and peers skyward. The other set is on the bottom of the head and looks into the watery depths.

Whirligig beetles are also well-constructed for swimming. The forelegs extend forward. The back pairs of legs look like little paddles. Even the shape of the beetle is a good one for a water insect. Its pointed front and tail ends make it look like a fat canoe. Even their antennae are reduced to miniature stubs so as not to produce drag when the insect is swimming — sort of like the Olympic swimmers who shave their bodies to increase speed through the water.

Adult whirligig beetles appear to like the company of their own kind. They often are seen swimming in large groups. When the gyrating mass of whirligig beetles is disturbed, some quickly dive while others swim off in a zig-zag fashion. This behavior appears to discourage predators set on having a beetle banquet.

People who handle whirligig beetles notice that the insect gives off an odor. This odor is likened by some to that of apple seeds and would appear to be used by the insect as a defensive chemical.

But turnabout is fair play. Whirligig beetles themselves are predators that feed on small insects that fall onto the surface of the water.

Watching these beetles gyrate in fresh water is no doubt a pastime of great antiquity to nature lovers. Indeed, the Hoosier poet James Whitcomb Riley had noticed their behavior and included it in the following lines.

“Little brook, sing to me:
Sing about a bumblebee
That tumbled from a lily-bell, and grumbled mumblingly
 Because he wet the film
Of his wings, and had to swim
While the water-bugs raced round and laughed at him”!

The water-bugs might have been racing around the bumblebee, but it is doubtful that these whirligig beetles were laughing. They were probably sizing up the bee as a potential meal!

 

Writer: Tom Turpin
Editor: Andrea McCann