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What Tiny Insects Reveal About Waterways

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Dr. Kevin Moulton, PhD in North Georgia
Photo Courtesy Susan Moulton

Navigating, hiking, and swimming skills are some non-so-obvious requirements for many research scientists.  Despite the long hours with microscopes and computers, most are also responsible for collecting their own specimens.  Although he sometimes has help, entomologist Kevin Moulton, PhD has spent long hours collecting insects for research projects. Recognized as an expert in flies or Diptera, he’s been especially interested in the midges that live in streams throughout the USA and Canada.

Dr. Moulton’s team from the University of Tennessee has been tracking new species of net-winged midge.  “If they leave their specialized habitat they’re not likely to find another suitable one. So they live basically in the stream corridor their entire lives. Unless you find them within a two-week window of when adults might be active, you’ll never see them.”  As youngsters in the larval stage, these creatures use tiny suction cups to attach themselves to smooth rocks in fast-flowing streams.  There they feed on algae called diatoms until they enter the pupal stage, where they grow wings.

Entomologist Kevin Moulton, PhD
University of Tennessee

Moulton has discovered first-hand how strong, yet sensitive, net-winged midges can be.  Once attached, larvae are difficult to pluck from substrates and pupae can’t be removed from their perch without killing them.  Yet, they need just the right conditions for their rocky homes.  “They can’t stand a lot of film, slime on the rocks because their suction cups won’t work.  It has to be a very smooth, polished rock face.  If it’s got a lot of organic matter in there, silt, whatever, from clearcutting up above the stream, they’ll disappear, because they can’t ‘do their thing.’ They can’t adhere to the rocks and scrape food off the rocks.”

Larger caddisflies and stoneflies prey on the net-winged midge’s larvae. Just as diatoms are indicators of stream health, so are the net-winged midges that depend on them for food.  Tracking these small creatures and other insects helps explain how in or out of balance our ecosystem is.  When some East Tennesseans complained that pesky black flies were bothering people around the French Broad and Pigeon Rivers, the state hired the UT team to come up with a science-based solution. They decided to use a substance in those waters that attacks the mid-gut lining of black flies, mosquitoes and a few other filter-feeding flies.  That project cut down on black flies that people considered pests over a five-year period.

As for the net-winged midges, most of us may never see these winged creatures first-hand because of their short life spans and specific aquatic habitat.  They not only don’t stray far from the streams, but they have no interest in biting people, despite generalizations about insects.  Painstaking work by Moulton and other entomologists ensures that we’ll at least have a snapshot of what the natural world looks like today, down to even the most modest of its members.

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