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Fri August 24, 2012
Dragonflies Winging South
Late summer brings cool nights and clear air - and winged migration. Along with birds heading south, there's a few butterfly, moth and dragonfly species that respond to the migratory urge.
One dragonfly - the common green darner - has been studied with results that suggest there's a lot of similarities between insect and bird migration. Tiny radio transmitters were attached with eyelash adhesive to green darners which were tracked by plane and ground crews.
The dragonflies fattened up or fueled up before departure, the same way that birds do. They also followed the same visual landmarks that guide birds south: the East Coast, major rivers and mountain ranges. Birds and dragonflies lay over for a few days, refueling or awaiting favorable flying conditions. Major flights come after a cold front that typically brings favorable winds from the north that assist their southward journey.
Another similarity: there's a resident green darner population that doesn't migrate, just as some bird species have stay-at-homes as well as migrants. There is one major difference between dragonflies and birds: the dragonflies that head south in the fall don't return in the spring. The green darners that reach their southern destination mate and lay eggs. It's the new generation that returns the following spring.
Coming soon to a yard or field near you is a swarm of dragonflies fanning out low in a swirl of activity, on the hunt for insects, mosquitoes included. Most likely these are residents, while the large migratory squadrons streaming south overhead, fast and orderly, are a sight all too rarely seen.