An icy winter blast has shut down many of the roads from Oklahoma to Michigan. That includes West Central Indiana where snow continues to fall. Very few insects are active outdoors during the winter months, but some, such as the winter stoneflies can be seen at this time of year. In clear, fast running streams, the water flows in spite of the cold and snow. The aquatic larvae of stoneflies remain active in the water which remains above freezing.
There are about 20 species of stoneflies that fly as adults between November and March in Indiana. Stoneflies are aquatic as larvae, feeding upon other invertebrates and detritus in clear streams with high oxygen levels. Stoneflies are often indicator species that reflect the health of the stream. Stoneflies will not live in polluted water with low oxygen levels. Absence of stoneflies from areas where they were previously abundant, indicates that the quality of the stream has deteriorated.
The association of stoneflies with stream quality is used by groups to promote concern about the environment and streams. For example, the Clinton River Watershed Council (North of Detroit, Michigan) hosts a Winter Stonefly Search in January. This is a great way to educate the public about insects and stream quality.
The best times to look for stoneflies are on warm sunny days in winter. Stoneflies can be seen basking on bridges that span highly oxygenated streams. For local readers, Little Pine Creek in Warren County, Indiana is a good location to observe these hardy insects.
Not all stoneflies fly during the winter. Some species fly in the summer and are attracted to lights like the one in the picture below. In some years, stoneflies are quite numerous and can congregate in large numbers on houses because they are attracted to outside lights. People should appreciate the stoneflies, because they are a sign of good environmental health.