Whirligig beetle (Genus Gyrinus)
This week’s crawly may have the most-fun-to-say-out-loud common name ever. Meet the whirligig beetle (Genus Gyrinus).
If you’ve spent any time around ponds, lakes, rivers and/or streams (and who of us hasn’t) you’ve most likely seen these bitty beetles in action, but probably haven’t been able to get a very good look at them.
They are worth taking a good look at! Whirligigs are just one fun fact after another. It’s hard to know where to start.
Let’s kick it off with their super fun name. If you haven’t yet seen a whirligig beetle in the wild, know that they come by that name honestly. They are tiny (just under one-quarter of an inch) perpetual motion machines.
In the water whirligig beetles zip and zoom around like miniature jet skis that have lost their riders. They do so in groups ranging from a handful of individuals to hundreds, and there’s a method to their maniacal motion. The movement confuses predators (and photographers!), who find it difficult to focus on any one individual.
Their evasion tactics are so effective it took me years of epic fails before I finally found a whirligig that would stop moving long enough for me to get a photo and finally be able to properly introduce them in a Crawlies column.
When it comes to avoiding becoming a snack for another arthropod, bird, fish or amphibian, whirligigs have many tricks up their proverbial sleeves.
In addition to their wicked cool dance moves, they use counter-shading to camouflage into their environment. When viewed from above their black elytra (wing covers) help them blend into the dark river bottom. If viewed from below, their underbelly looks pale, blending into the sky.
If movement and color aren’t enough to ward off a would-be predator, whirligigs emit a nasty compound which leaves a literal bad taste in the mouth of any critter that makes a snack of one. A trout may eat a single whirligig beetle, but won’t be fooled again and try a second.
But wait! There’s more! As if all those defenses weren’t enough, we’ve saved the coolest for last. Whirligig beetles have four compound eyes. One set is on top of their head helping them spot possible predators – and their own prey – above the water’s surface. Their second pair of eyes is underneath the top-viewing pair scanning for death from below.
All of these defenses allow whirligig beetles to spend less time and energy on avoiding predators and more on being predators.
Whirligig beetles are like little packs of aquatic hyenas. If a non-aquatic arthropod gets stuck in the film on the water’s surface, whirligig beetles will surround them and have a buffet. Whirligigs are very social critters, willing to share a meal. Often several different species of whirligig will hang out together to hunt and dine. They aren’t picky and will chomp down live or dead prey.
Their teeny mandibles were made for that carnivore life and their paddle-shaped forelegs are equipped with small hooks at the front so they can really hold on to their meal.
They’ll also dine on other aquatic arthropods, such as mosquito larvae, who must come to the surface to get a breath of air. Whirligigs are firmly in the “beneficial insect” category.
Their larvae are also carnivorous and eat other aquatic arthropods, especially soft-bodied ones.
Female whirligigs lay eggs on the surface of aquatic plants. The larvae live underwater until they are mature enough to morph into their cocoon and then their final winged form. Larvae will leave the water and make their cocoons on the stems of streamside plants.
When they emerge in adult form, they’ll zip right into the water if the source is still there. If their natal pond or stream has dried up, they’ll spread their new wings and fly until they find a new pond, stream or river to call home, and then their literal Dance of Death begins.