Last week the mystery and allure of the Geneva Snake grew too strong to resist; I had to go check things out for myself. And while the snake itself proved elusive, I did see lots of other cool things: Argiope (a.k.a. “garden” or “banana”) spiders’ intricate work—delicate webs complete with a trademark “zipper” in the middle. A giant catfish (maybe bullhead?) prowling the shallows of a pond, its back breaching the water’s surface just like a miniature Loch Ness monster. Great blue herons, great egrets and even a little green heron feasting on an abundance of frogs—the likes of which could surely account for sightings of big fat snakes in the area.
But then imagine my surprise when, as I’m preoccupied with thoughts of reptiles, I should run into an old acquaintance: Good ol’ water beetles. A boatload of ’em! Literally.
A pedal boat was beached at one end of a retention pond, and each of the seat wells had filled with rainwater. Skittering among the rocks someone had placed in the boat were several dark, shiny, elliptical insects. At first I thought they were whirligig beetles—a personal favorite. But as I watched them I noticed their bodies were a little plumper and more rounded than would be conducive for the spinning movements of a whirligig.
I reached into the water—warm, stagnant stuff that I thought for sure would be loaded with mosquito larvae, but wasn’t. I tried to grab one of the beetles, but came up empty. Grabbed again, same result. After several more futile attempts I finally got smart and removed the rocks from one well, thus taking away the hiding places that were thwarting my efforts. It wasn’t long before I caught a beetle. Yay!
Then it flew away. Boo!
Adapting my technique one more time, I caught a beetle, snapped some quick pictures and then replaced it, along with the hidey-place rocks, into the boat.
Back at home I loaded the pictures I’d taken onto my laptop, where I could see the details a lot better. What I realized I’d found were water scavenger beetles—members of the family Hydrophilidae, the water lovers.
What looks like two sets of antennae on these guys actually are one pair of antennae and one pair of long, thin tactile appendages called palps. But as is so often the case with nature in general, what you see is only half the story.
The antennae, which provide important sensory input, also serve to keep the oxygen-breathing insects alive while underwater. Using the clubbed antennae like little brooms, the beetles rise to the water’s surface and “sweep” air beneath their bodies. It’s held there as a bubble and used as a mini oxygen tank as the insects go diving and swimming in search of food.
The air bubble, being clear and shiny, gives the impression that these beetles have a light-colored underbelly. It also gives rise to the common name silver water beetle.
While their other common name, water scavenger beetle, would appear to provide some insight into just what these critters eat, that name is somewhat misleading. The adult beetles do scavenge, eating dead plants and animals; but, depending on species, they may also be predatory—which may help explain the absence of mosquito larvae in what sure looked to be perfect habitat for them.
Regardless of species, all baby water scavenger beetles are predators. Amazing ones, at that.
Hydrophilid larvae have curved, pointy mandibles that are perfectly adapted for grabbing and piercing a number of types of prey, ranging from tadpoles and snails to those pesky baby mosquitoes—tiny aquatic creatures also known as “wigglers” because of their frequent writhing near the water’s surface.
I’m kicking myself that I didn’t explore the water’s edge a little more thoroughly that day I visited Geneva. It was steamy, and I got pretty warm. But I’d have liked to have seen if I could find some of these larvae, along with more adults—just to see if I could identify them at least to genus.
With the cooler temperatures that have moved in, I may try to head back this weekend to look for beetle larvae, preying. And adult beetles, scavenging. Oh and maybe, if I’m lucky, large snakes, basking.
Pam Erickson Otto is the manager of nature programs and interpretive services at the Hickory Knolls Discovery Center, a facility of the St. Charles Park District. She can be reached at 630-513-4346 or potto@stcparks.org.
September 11, 2015
Water Scavenger
Beetles
Water scavenger beetles may look like they have two pairs of antennae, but one set—the longer, thinner pair—actually are sensory appendages called palps. The shorter, clubbed antennae serve several important functions, as also help curious naturalists differentiate these insects from the similar predaceous diving beetles.