April 22, 2016
Gigantic Caddisfly
This week’s column actually had its beginnings last summer, though I didn’t know it at the time.
I can still picture it: The warm July sun streaming down, the flowers shimmering in the bright light. I could feel the heat beginning to build even though it was barely 8 a.m. As I listened to the bumblebees and honeybees swirling around the St. John’s wort, I realized it was going to be a buggy sort of day. A ground beetle scurried away from the remnants of his multi-legged meal. A dragonfly hovered above the rain garden.
I stopped briefly to watch a mass of pavement ants, already in an uproar despite the early hour, when I realized I was not only surrounded by insects but also had been selected by one in particular.
This however wasn’t just any old bug—as if there really were such a thing. Nope, this was an insect unlike anything I’d seen before.
Well, mostly unlike… It did remind me of something—an insect you’re probably familiar with even if you don’t know what it is: A caddisfly.
Most people refer to these guys as “river bugs,” as they’re often associated with riparian environments. We have a few species that predominate in the Fox River, and when the adults emerge, en masse, the air is thick with millions of small, moth-ish insects that swirl around very much like brown snowflakes. (The analogy doesn’t end there. In years when emergences are especially large, the best way to clean the bodies up is with —yep, you guessed it—a snow shovel.)
At any rate, the caddisflies with which we’re all most familiar are small, maybe a half inch in length. But this creature, which had adopted my leg as a landing point, was much larger. Its length, including wings, was well over an inch long; including the antennae up front I was looking at more than two inches of insect.
That day I didn’t have a whole lot of time to devote to field guides, so I settled on a tentative and nonspecific “Gigantic Caddisfly” and left it at that.
Then, last weekend, I took a dip net out to a nearby wetland and the story came full circle.
I was with my friend Jessi, an aquatic ecologist, and we actually were on a mission to find fairy shrimp. (We didn’t find any, this time. But when we do, expect to hear about it. Fairy shrimp are awesome!)
Wading in the still-chilly water, we immediately found clusters of frog eggs. We saw cool plants like bladderwort (which is carnivorous and might also merit a column of its own some day soon) and cool arachnids like a young and freshly molted fishing spider (likewise).
Then Jessi pointed out something that, had I been alone, I would have dismissed as a large clump of wetland debris. Except that it was moving along under its own power, determinedly making its way up an underwater stalk of grass. A caddisfly larva!
These plump, juicy little juveniles are the caterpillars of the underwater world. It’s not surprising then that, like caterpillars, caddis larvae are attractive prey for any number of insectivores. It’s vital to their survival that they outsmart their predators. And they do, in a number of innovative ways that always make me think of The Three Little Pigs.
Caddisfly larvae variously build cases out of plant stems, sticks or stones; their selections are species specific. Materials are collected and glued together with a sticky silk produced by glands near the mouth. The result is a tough, tube-like case that helps protect the soft-bodied larva from the huffing and puffing of predators like The Big Bad Wolf… Spider…
Jessi and I spent the afternoon ooh-ing and aah-ing over the caddis larvae—we came across many more—and their marvelous ways. But it wasn’t until I got home and was clicking through the photos on my camera, deleting the blurry ones, that the significance of our find became clear.
Those larvae, bedecked in bits of leaves and stems, will soon pupate and metamorphose into the same sort of Gigantic Caddisfly that found me last summer.
While I will defer to the experts when it comes to specifics (North America is home to more than 1,350 caddisfly species) I’m pretty sure the ones we found are members of the family Limnephilidae. (Like the bugs themselves, the etymology of that name is pretty awesome. Limne is from the Greek for pool or marsh, and philos means loving.)
Come July, when the days turn muggy and buggy, the adult caddisflies will take to the air. This time, armed with a field guide, I’ll be ready to make a more accurate ID. With only 300 or so Limnephilidae species to pick from, how hard could it be?
Pam 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.
A cousin of the small, brown ‘river bugs’ everyone is familiar with, this marsh-dwelling caddisfly is much larger. As a caterpillar-like juvenile it lives in water and constructs a protective case made from bits of plant material.