Creatures with six legs and three tails found in the Potomac River

It was a blustery February afternoon, but I wanted out. I’d go down to the river to see what I could find.

I threw my waders into the back of my car and headed to Carderock, in Bethesda. A short hike down the Billy Goat Trail I found a likely place and slid down the riverbank, using exposed tree roots as handholds. My boots hit the mud.

A few feet out from shore I plunged my arm into the icy water to grab a large, flat rock. I tipped it up on its end and inspected every nook and cranny. In the summer on such a rock I would find all manner of tiny crawling things, mostly the larval forms of insects. With their multi-spiked tales, armored bodies, and fearsome jaws, they look like monsters in a low-budget horror movie.

Several stones later my hands began to grow numb and I gave up.

Citizen science. I would find my monsters at the nearby Audubon Naturalist Society (ANS) in a class with a fittingly awe-inspiring name: “Benthic Macroinvertebrate Identification.”

Cathy Wiss focuses in
on a six-legged specimen.

The classroom was filled with people of all ages, all eager to learn how these little creatures lived and how to identify them. After the course ends many of the students will go on to collect specimens in streams and record their findings. Different species have different tolerances to pollution, so their presence or absence says something about the quality of the water.

Probably no group of such “citizen scientists” except birdwatchers makes a greater contribution to our knowledge of the environment than these stream monitors. Many schools in the Potomac region and across the country make macroinvertebrates a part of science education. It’s a way to experience nature in the raw and do some real-life data collection.

Bottom dwellers. I leaned over my microscope to examine the tiny creatures while inhaling the alcohol fumes in which they took their last swim.

Cathy Wiss, ANS Water Quality Monitoring Program Coordinator, dissected the name of the course. The term “macro,” means anything you can see with a naked eye. “Invertebrate” refers to anything without a backbone, in this case, mostly insect larvae. The initial word in the course name was “benthic.” It simply means that these particular insect larvae live on the bottom of our rivers and streams, under rocks, in the mud, or hidden among the roots of weeds.

A microscopic world
of macroinvertebrates.

Conducting the class this week was ANS stream monitor Gretchen Schwartz. Her subject was one particular group of macroinvertebrates called Trichoptera, the caddis flies.

Enlarged by the lens, many of them looked a little like tiny, elongated shrimp with curved bodies and six legs poking out of their thorax. But actually they are most closely related to moths and butterflies. They live their larval lives in the water. After they hatch into flying adults they live on nectar, at least for the few days until they mate and lay their eggs. Then they die.

Nets of silk. Schwartz told us other things about Trichoptera that once again showed nature’s infinite variety and inexhaustible ingenuity.

Different species make their living in different ways. Some scrape algae off of rocks. Others shred up leaves and eat them. Aggressive predators seize and consume other macroinvertebrates.

Some species even make silk to fashion delicate nets. Some set the nets on the stream bottom to catch any edibles coming their way. Others use silk strands as kind of lifeline to hold them to the bottom in fast currents.

Still other Trichoptera species use this same silk to make dwellings, wrapping it around grains of sand and then tying grains together to form a tube that they wear as a kind of a flour sack. Some enthusiasts give colored grains to captive Trichoptera. The insects use them to make their tubes, which people fashion into earrings. It could be a conversation starter or stopper, depending on the company.

Beyond useful and clever, these macrointertebrates are also extremely important. They and countless billions of other tiny creatures are what renowned Harvard biologist E.O. Wilson calls “the little creepy-crawlies that run the earth.” If Pandas or elephants—or us—suddenly disappeared, life on earth would pretty much go on. But remove bees and ants—and benthic macroinvertebrates—and our ecosystems would collapse in a hurry.

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