Small Bug is Big Sign of Stream Health

Nature Academy

On a typical day at the parks, you may see many different species of animals and birds, such as white-tailed deer, turkeys or wood ducks. But the parks are also home to many interesting and important aquatic organisms that you might never notice if you don’t stop to take a closer look. Take this “little” insect for example…

A dobsonfly in its larval form found in Dry Fork Creek at Miami Whitewater Forest

A dobsonfly in its larval form found in Dry Fork Creek at Miami Whitewater Forest


Meet the dobsonfly. Also known as a “hellgrammite,” the dobsonfly is often used by stream and river anglers as bait for fish such as smallmouth bass. A typical dobsonfly larvae can be anywhere from 2–5 inches long with gray or brown coloration for blending in with stream substrates. The conspicuously large pincers on its head are used for feeding on small aquatic invertebrates.

Dobsonflies are typically the largest predatory invertebrate in Park District streams. Large predators in any ecosystem are usually less abundant than their prey, and dobsonflies are no exception. So while you may be able to find hundreds, or even thousands, of other aquatic insect species in a small section of stream, dobsonflies are much less common. They may stay in a stream for two to five years, only emerging for approximately a week to mate and deposit eggs before they die.

So how are these little beauties actually important to us? Well it turns out that dobsonflies are really good indicators of water quality. Dobsonflies are intolerant of pollutants in their environment. Their presence typically indicates a high-quality ecosystem with little to no pollution. Their absence, however, could be an indication of physical or chemical pollutants in the stream. The Stream Monitoring Program, staffed by Park District volunteers, monitors for pollution-intolerant species such as the dobsonfly to keep track of what is happening in our streams and their associated watersheds.

So if you are lucky enough to spot a dobsonfly in one of the Park District streams, now you’ll know a little more about the health of its environment.

Ben Braeutigam, Stewardship Technician