Thousands of fans headed to Sun Life Stadium in Miami, Florida last weekend to watch a football game between the University of Miami and Kansas State. The fans were disappointed that the game was delayed by lightning, but were rewarded for their patience with a special treat. Swarms of dragonflies visited the stadium swooping down on mosquitoes and according to one fan, took over the student section. Some of the unappreciative fans swatted them away.
The dragonfly swarms are part of a large North American migration that occurs every fall as Common Green Darners, Ajax junius, fly South for the winter. The Common Green Darner develops rapidly. Eggs laid in the North in the Spring will develop into adults that fly South for the winter and lay eggs. Eggs laid in the South will develop into adults that will later migrate north. No one individual makes the entire round trip.
Scientists interested in migration have been studying the Common Green Darner. They are large enough to be equipped with miniature radio transmitters and followed by tracking airplanes. (For example, Wikelski et al., 2006; doi: 10.1098/rsbl.2006.0487) The dragonflies migrate about 10 km per day and only fly during the day. Migration is in a general trend southward and is promoted by cool nights.
People who live in the Northern US in summer and migrate to Florida for the winter are following the path blazed by dragonflies long, long ago.