Invertebrate Investigators

by Jon Markovich

In the previous Healthy Waters blog, my colleague Micka Peck wrote about the stream sampling we did for benthic macroinvertebrates. Pulling on a pair of waders and kicking around in the stream sampling was only half the fun.  After the outdoor fieldwork, I changed wardrobe from field gear to lab coat. Ok, I didn’t really wear a lab coat, but I was in a lab processing the preserved macroinvertebrates for later identification.

It’s been established that macroinvertebrates are good indicators of water quality conditions. Identifying which macroinvertebrates are present in a stream sample provides a link to determining whether a stream has good water quality and supports a healthy aquatic community.

One sample collected from a stream can have hundreds, even thousands, of macroinvertebrates. Thankfully, my target was to process a small sub-sample – around 200 individuals. This involves spreading the entire sample onto a gridded pan, randomly selecting a grid and removing all materials within it, and “picking” through the leaves, dirt, gravel, and other debris to separate out macroinvertebrates. At times, it felt as though I was playing a game of “Where’s Waldo?” In this case, “Waldo” could have no tails, two tails, or three tails, gills or no gills, or a whole number of different features. Sorting through these samples is no joke – it takes serious skill to quickly pick out bugs from non-bug debris. But after they’ve been picked from the sub-samples, the macroinvertebrates are identified under a microscope.

Looking under the scope, I marveled at these creatures. The different features and shapes of each bug were jaw-dropping. One bug, a burrowing mayfly in the family Ephemeridae, has protruding tusks on the side of its mouth like an elephant. The tusks help this family of mayfly to burrow into soft sediment to feed. Another bug, a dragonfly in the family Aeshnidae, had a hinged-mouth that extended to be nearly half the length of its body! Dragonfly larvae are predatory and this super-extendable mouthpart allows them to quickly snap up prey. These kinds of distinguishing features and characteristics are what scientists look at under the microscope for macroinvertebrate identification.

Although they look way cooler under a microscope, you don’t need one to see macroinvertebrates. If you have the chance, go check out your local stream, flip over rocks and search the stream bottom. You too could become an invertebrate investigator!


About the Author: Jon Markovich joined EPA’s Water Protection Division in 2014 and works in the impaired waters and Total Maximum Daily Load programs. In his spare time, Jon enjoys hiking, kayaking and camping in the Mid-Atlantic Region’s many great state parks.

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