This radar image is a swarm of butterflies captured in St. Louis on September 19.
The great migration has begun! While many birds migrate to southern climes to overwinter, the migration of monarch butterflies can be so dramatic and impressive, people gather at popular viewing sites to see the sky darken with winged beauties and swarms can be tracked by weather radar. In spite of a tough year, due to drought, lack of milkweed and an extremely cold winter, Monarchs still move en masse to their winter home in Mexico
A particularly large swarm was captured by radar over southern Illinois and central Missouri this week. The National Weather Service in St. Louis determined they were looking at butterflies due to the high differential reflectivity and low correlation coefficient values which indicate a biological target. High differential reflectivity usual indicates an oblate object (spheroid with flattening at poles) while low correlation coefficient values mean that the objects are changing shape. Monarch butterflies would appear oblate when picked up by radar and flapping wings would account for the changing shape. Other insect swarms have been captured on radar (and been discussed here) including mayflies in Wisconsin and grasshoppers in New Mexico.
Radar is rapidly becoming a useful tool for scientists to track movements of birds, bats and insects. This data may just clutter up radar for meteorologists, but can be vital for studying the sometimes difficult to quantify flying animals. And with pollinators, such as birds, bats and butterflies imperiled every bit of data can be crucial to their preservation.
