Every summer laughing, shrieking children fill the rivers of Vermont. They swim, they splash, they catch minnows in butterfly nets - and they have no idea that they are wading through a world of hidden life. Beneath their feet lurk thousands of strange-looking creatures called benthic macroinvertebrates.

These tiny insects spend the first part of their lives underwater, before crawling out on shore to shed their skins and fly away. The health of a stream can often be determined by the health of the Benthic macroinvertebrates that inhabit it.

Recently, my class went on a field trip to Baldwin Creek to measure the health of the stream. Each group was assigned a cross-section, which the group members then tested in many areas, such as water temperature, conductivity, dissolved oxygen, and pH level. With the help of Chris Runcie (LCA representative), we collected a sample of benthic macroinvertebrates from each cross-section.

We found many different types of aquatic life, including stoneflies, mayflies, caddisflies, dragonflies, Dobsonflies (hellgrammites), crane flies and snipe flies. Everyone was surprised to find that these nymphs looked nothing like flies, because in this stage they have not yet grown wings.

We also discovered beetles, aquatic worms, and water striders. Of these species, caddisflies, mayflies, stoneflies, and hellgrammites have very low pollution tolerance. Dragonflies and crane flies have moderate tolerance, and only aquatic worms have high tolerance. Because many of the species we collected had low pollution tolerance, this would seem to indicate that Baldwin Creek is a very clean stream.

Although the insects I listed are the only ones we found in the stream, it is likely that there are others we missed, hidden under the rocks and the many splashing feet. That is the mystery of benthic macroinvertebrates - you never know they’re there until you look. So keep this in mind the next time you go swimming!