Fisheries, Midwest Region
Conserving America's Fisheries

Image Mayfly Emergent
Mayfly Emergent Credit: USFWS

Image Doppler Weather Radar
Doppler weather radar image of mayfly emergence from the Upper Mississippi River near La Crosse, WI. Credit: National Weather Service

Sentinels of Environmental Health
Mayflies (Hexagenia)

Mayflies are a major component of the native invertebrate community that inhabit the Upper Mississippi River and many of its tributaries, as well as other large rivers and lakes in North America. Burrowing mayflies are sensitive to gross organic pollution and do not tolerate low levels of dissolved oxygen. Annual observations of mayfly abundance in portions of the river can serve as indicators of the relative biological health of the Upper Mississippi River.

As nymphs, these aquatic insects proceed through one or two years of larval development as filter feeders, consuming decaying organic matter at the river bottom. In summer, large numbers of nymphs synchronously emerge from the water at dusk and take flight as subadults. Within 36 hours of emergence, the subadults metamorphose into adults that subsequently swarm in the air to mate before returning to the water surface to lay their eggs and die. Some of these emergence events are so large and widespread that swarms can be detected by Doppler weather radar.

Help Wanted - Play a Part!

You can help monitor the health of the Upper Mississippi River, and experience a natural phenomenon seldom encountered in other parts of the world, by reporting mayfly emergence events you happen to observe.

Whether you reside, travel, work, or recreate near the river, sending a brief report of mayfly emergence events can help resource managers maintain a finger on the seasonal pulse of this dynamic ecosystem.

Become a Mayfly Emergence Reporter

2016 Emergent Mayfly Observation Form

UMR Mayfly Emergence and Development Synopses: 2012 - 2013

UMR Mayfly Emergence and Development Synopses: 2013 - 2014

An alternative means to participate as a mayfly emergence observer this year and in the future is through the National Phenology Network - Nature's Notebook web site. Developed in cooperation with the National Wildlife Refuge System and the Upper Mississippi River National Wildlife and Fish Refuge. Those interested in participating via this 21st Century electronic option can use smart phones, androids, laptops, or PCs to enter their observations directly into a national database that is maintained by the USGS and the University of Arizona.

To learn more about the Mayfly Watch Campaign view the National Phenology Network You-tube video production.








Last updated: September 5, 2018