What bugs tell us about water quality

There’s a lot you can learn about our local streams if you’re willing to get a little wet and flip a few rocks.

While it’s trout that get all the attention on Northern Michigan’s river systems — we do call them trout streams, after all — there would be no trout to speak of without macroinvertebrates.

By definition, macroinvertebrates include any river creature that lacks a backbone and can be seen without the aid of a microscope or magnifying glass. This includes the larval or nymph stages of flying insects, and we can use their presence and diversity to gauge a stream’s health.

GALLERY: Aquatic insects of the Pigeon, Thunder Bay Rivers

Three taxonomic groups of nymphs are considered “indicator species” for healthy water. Scientists who study rivers have turned these three groups  — ephemeroptera, plecoptera and trichoptera, abbreviated as EPT — into a tool known as the EPT Index.

Macroinvertebrate specimens, preserved in vials of ethanol, are used alongside a flow chart to identify aquatic insects collected from a stream. The presence of certain insect species is an indicator of good water quality.

“These are our mayflies, stoneflies and caddisflies, and they are the most intolerant of poor water quality,” said Dylan Loop, Coastal Restoration Technician for Huron Pines in Alpena, who has done this kind of research in his past work with the Great Lakes Coastal Wetland Monitoring Program. “Collecting and counting their nymphs is faster and easier than testing water samples in a laboratory.”

Mayflies, stoneflies and caddisflies may spend years hiding in the streambed, clinging to logs or rocks or burrowed in silt. They eat algae, bits of plant matter and other detritus, contributing in their own way to stream health by breaking down organic matter into smaller bits that can be used by creatures lower on the food chain.

They are also highly sensitive to changes in water quality and will die if a river gets too warm, low in oxygen, or polluted by surface runoff. Of all a river’s creatures, they are among the first to go. They are the so-called “canary in the coal mine” and their absence means something is wrong. It should also be noted that they are very good at hiding.

Participants with Presque Isle County 4-H use dip nets to collect macroinvertebrates from the Ocqueoc River with Huron Pines in August.

Simply put, more bugs means a healthier stream. It’s a fact long understood by fly anglers, who “match the hatch” at specific times of the year by casting flies resembling the larval or adult versions of whichever species is hatching on a given day. Trout, a river’s top predator, key in on these hatches to feed, and anglers follow close behind.

Nick Theisen is one of those anglers. He was introduced to macroinvertebrates as a student in the Entomology Lab at Michigan State University and started fly fishing and tying flies soon after. As part of his service with Huron Pines AmeriCorps, he familiarizes others with macroinvertebrates by training volunteer stream monitors or teaching youth how nymphs relate to stream health.

Jenna Nowicki (l) and Catt Knoch with the Boys & Girls Club of Alpena arrange some macroinvertebrates onto a dish after collecting them from the Thunder Bay River in August.

Theisen and Huron Pines Water Program Director Samantha Nellis led two such workshops in August with Alpena Boys & Girls Club on the Thunder Bay River, and Presque Isle County 4-H on the Ocqueoc River. They used dip nets to collect nymphs from the stream and utilized a flowchart to identify each one by its physical characteristics. Those events were supported in part by the Consumers Energy Foundation.

“Macroinvertebrates are a really fun introduction to stream science,” Theisen said. “They’re so easily overlooked but if you look close enough while flipping rocks or overturning logs, you’ll find more life than you’d ever expect.”

If you’re interested in collecting macroinvertebrates, you’ll need a sturdy butterfly net, a shallow container and a hand lens to see details for identification. Be sure to place rocks, logs and nymphs back in their original location in order to preserve their habitat and population. Identifying information and illustrations can be found at macroinvertebrates.org.

3 thoughts on “What bugs tell us about water quality

  1. If you need an adult volunteer to assist with the macro invertebrate class or collection, let me know. I can help. I’m near Millersburg, so the Ocqueoc river would be great.

    1. Thank you. We don’t have another macro day scheduled, but we had a great time and might do more in the future so we’ll definitely keep you posted.

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