Mayfly Mating Tango Captured by NWS Detroit/Pontiac Doppler Radar!

Each year in late June and early July, mayflies (Hexagenia) swarm along the Lake St. Clair (as well as other lakes) shoreline. The mud-burrowing mayfly (the largest species) "hatch" in the mudflats along the lakeshore. During their brief lifespan (no more than a couple of days, and typically only a few hours), these insects perform an airborne mating ritual. A recent aerial courtship was captured by NWS Doppler radar on Tuesday, July 26, 2001.

The mayflies synchronously appear around sunset (Darkness provides safety from predators -- birds love 'em for their protein) and "swarm". Each swarm consists of hundreds or thousands of flies. Once airborne, the flies mate, with the male dying off shortly thereafter. The female then drops her eggs (numbering in the thousands), over the Lake, darting toward and away from the lake surface.

This sequence of NWS Detroit/Pontiac Doppler radar images shows the flies beginning their swarm, then continuing for a couple of hours.

Figure 1.  National Weather Service Doppler radar reflectivity image valid June 26, 2001 at 921 pm. First evidence of mayfly swarm just east of Mt. Clemens near the Lake St. Clair shoreline.
Figure 2.  National Weather Service Doppler radar reflectivity image valid June 26, 2001 at 931 pm. Main swarm now located in the northwest corner of Anchor Bay, with other possible swarms evident southeast of New Haven and over Harsens Island.
Figure 3.  National Weather Service Doppler radar reflectivity image valid June 26, 2001 at 941 pm. Swarm now reaches in an arc from northwest Anchor Bay through far southeast Macomb County and into southern St. Clair County. Darkest reds indicate highest density within swarm.
Figure 4.  National Weather Service Doppler radar reflectivity image valid June 26, 2001 at 950 pm. Similar location to Figure 3, but swarm shows some broadening.
Figure 5.  National Weather Service Doppler radar reflectivity image valid June 26, 2001 at 1000 pm. Swarm now entirely located over St. Clair County with very high reflectivity returns (darkest reds and purples) suggesting dense swarm.
Figure 6.  National Weather Service Doppler radar reflectivity image valid June 26, 2001 at 1059 pm. Swarm now largely over Lake St. Clair  -- suggestive that mating has taken place and females are now laying eggs over Lake St. Clair.

Created: June 27, 2001


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