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March 18, 2014

What Do Your Creek’s Insects Tell You About Its Environmental Health?

Many watershed coordinators, ecofriendly crowdfunders, and other environmental activists are accustomed to the realities of working with limited resources. It’s simply not practical to throw everything at your creek’s problems and hope that something will improve its health. Instead, you need to be able to identify specific problems to target and fix.

Illustration by Jonathan Wilson.

There are many ways to pinpoint environmental problems, from walking along creeks spotting litter to testing their waters for the presence of harmful chemicals. Observing the populations of certain insects in your watershed is another means of gathering valuable insight about your watershed’s health. Although no single indicator of environmental health should be looked at as a “crystal ball”, unusually high or low populations of certain insects can be a fairly reliable indicator of certain environmental problems.

Water quality is one of the most important things that insect populations can tell us. Some insects, like mayflies and stoneflies, are able to survive only in waters with low levels of pollution–in fact, some species of stoneflies are so sensitive that their presence is considered a sign of extremely good water quality. Other species, like leeches and blackfly larvae, are capable of surviving even in extremely polluted waters. The presence of these species, combined with the absence of others, is usually a sign of very poor water quality.

Caddisfly at light 29.10.11 Kilnsea

Photo by Petros Pete.

Insect populations can also give us valuable information about water temperatures. Water temperature is not always an easy issue to fix, but a sudden rise in water temperature could be a sign that an upstream factory or other facility is not complying with federal regulations. Unusually abundant caddisflies, while a welcome sight to fly fishermen, can be a sign of rising water temperatures in a creekbed. Conversely, a sudden drop in caddisfly numbers can be a sign that water temperatures are falling.

Not all of the insects that tell us about our watersheds’ environmental health are aquatic. Indeed, a dramatic rise or fall in the number of any insect from stoneflies to butterflies can send a message about a number of environmental problems. These rises and falls can signal changes in pollution levels, food sources, predators, and breeding or hatching sites.

Illustration by Lydia Nichols.

Again, it would be a mistake to interpret a change in insect populations as a surefire sign that your watershed is suffering from a particular problem. However, insect populations are an important piece of evidence that can help your watershed’s environmental guardians pinpoint the problems that it faces. Paying attention to these populations–or better yet, crowdfunding a scientific study of the populations in your community–can be an important step toward pinpointing your watershed’s most important environmental health concerns.

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Posted by Mark Contorno.

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