Aquatic Insects, Harbingers of Health

Aquatic Insects, Harbingers of Health
Skwala (Large Springflies)
Stonefly Nymph
Courtesy & Copyright
Robert Newell
As found on

Aquatic Insects, Harbingers of HealthMayfly nymph
Courtesy & Copyright
Leo Kenney, Vernal Pool Association

Aquatic Insects, Harbingers of HealthNorthern caddisfly Larvae

Photo Credit:
Howard Ensign Evans,
Colorado State University,
Used under
Creative Commons Attribution 3.0

Hi, this is Mark Larese-Casanova from the Utah Master Naturalist Program at Utah State University Extension.

As we officially enter summer, it’s easy to notice nature at its peak. Wildflowers are in bloom, birds are feeding their young, and insects fill the air. Life is especially robust near our wetlands, lakes, and streams.

Our aquatic, or wet, ecosystems provide habitat to abundant plants and animals. Only 1% of Utah is wet, but over 80% of all wildlife in Utah depend on aquatic ecosystems for at least part of their life cycle. However, the quality of Utah’s aquatic habitats is often affected by chemical pollution or excessive nutrients and sediment.

Some organisms, including many aquatic insects, only live in the healthiest of aquatic habitats. Many of the insects we see in summer live in the water when young, during the larval or nymph stage, before becoming adults. Three insects in particular- mayflies, stoneflies, and caddisflies- require especially clean, cold streams low in nutrients and high in dissolved oxygen to survive.

Mayflies are aquatic as nymphs and emerge from the water to live as adults for just a day. The external feather-like gills of the nymphs can be seen fluttering along the sides of their abdomen. They feed by scraping algae from rocks.

Stonefly nymphs are well adapted to living among the rocks of swift-moving streams. Their hooked legs grasp the slick rocks as they shred apart plant litter that falls into the stream.

Caddisfly larvae spin a sort of spider silk to glue rocks or sticks together to form a case in which they live. They will also build webs underwater to collect small particles of food that drift by.

The quality of a stream habitat can be assessed by counting the number of different species, or types, of mayflies, stoneflies, and caddisflies. A greater number of species generally means that habitat and water quality are higher. Dramatic decreases in insect diversity from season to season or year to year can signal a decline in stream health. Monitoring aquatic insects over time gives us an accurate picture of the long-term health of our stream ecosystems.

For more information about monitoring water quality and aquatic insects, visit Utah State University Water Quality Extension’s website. Once there, you’ll find a wealth of information about monitoring Utah’s aquatic ecosystems, including Utah Water Watch, a statewide volunteer citizen science program.

For Wild About Utah, I’m Mark Larese-Casanova.

Images: Northern caddisfly larvae, Howard Ensign Evans,
            Colorado State University
            Creative Commons Attribution 3.0 License.
            Stonefly Nymph, © Robert Newell, displayed on
            Mayfly nymph, © Leo Kenney Vernal Pool Association
Text:     Mark Larese-Casanova, Utah Master Naturalist Program
            at Utah State University Extension.

Additional Reading:

Larese-Casanova, M. Utah Master Naturalist Watersheds Wildlife Field Guide. Utah State University Extension. 2012.

USU Water Quality Extension. Utah Stream Team Manual.

Voshell, J. R. A Guide to Common Freshwater Invertebrates of North America. The McDonald and Woddward Publishing Company. 2002.