Mayflies Make a Summer Splash

The summer season for Arlington’s Volunteer Stream Monitoring Program came to a close on Aug. 3. We were blessed with beautiful weather during the entire monitoring period and had ample bugs to count at every monitoring site. The stream monitoring program studies macroinvertebrates  the small organisms that live underwater in our streams, lack a backbone and can be seen with the naked eye. These “stream bugs” live a portion of their life cycle in streams and depend on the stream ecosystem for habitat and food. Some macroinvertebrates are more tolerant of stream pollution than others, which makes them good indicators of water quality. All of the photos below were taken by volunteer photographer Nick Leach.

Stream monitors with nets, boots and buckets.

Stream monitor looking at macroinvertebrates.

A summer stream monitor.

Stream monitor chemistry tests.

Volunteers perform several water chemistry tests during each monitoring session.

Stream monitors net picking.

The bugs often cling to the net, making “net picking” an important step.

Right about the time we were completing our summer monitoring, mayflies were making national news for their massive numbers in the Upper Midwest. Mayflies were the most abundant bug at each of our nine monitoring sites, but our numbers were nothing like what the Midwest has been experiencing.

Mayflies in a tray.

Can you find the two mayflies in the ice cube compartment above?

There are more than 130 species of mayflies in the U.S. according to J. Reese Voshell’s guidebook, A Guide to Common Freshwater Invertebrates of North America. Only one type of mayfly has been documented in Arlington, the small minnow mayfly. While mayflies are generally considered to be sensitive organisms and indicators of good water quality, the small minnow mayfly is an exception. The small minnow mayfly is able to survive the impacts of stormwater runoff and the pollutants stormwater carries, making it a more tolerant mayfly than some of its more sensitive relatives.