I am writing this in mid-September while enjoying the sights and sounds of early Fall in the Blue Ridge Mountains. At this time, many of our breeding birds have left and migration is well underway so that there is little bird song in the woods and fields. Fall flowers are in full bloom and insects are scurrying around frantically as if they know that their time to reap is limited before the first frost. All of you are well aware of the massive movements of breeding birds (neo-tropical migrants) from North America to Central and South America for the Winter. Everyone is also aware of the fantastic migration of our monarch butterflies to the mountains of Mexico for hibernation. However very few may be aware of a truly remarkable seasonal migration of dragonflies which becomes obvious if you carefully observe the types of insects that are passing through your area.
I first notice that dragonflies are migrating when our common large green darners (see photo of a male holding a female while she lays eggs) suddenly disappear from our ponds. In place of these well-known green and blue mosquito-eaters there suddenly is another large dragonfly present, the shadow darner (see photo of me holding a beautiful male). It would almost seem that the departure of the dominant green darners is followed by replacement by the very cold-tolerant shadow darners that occupy a very similar niche, but at a different time. Now I am assuming that the shadow darners are emerging from nymphs that live in our ponds, but I cannot be sure of that- some may migrate to our location. Some dragonflies have the ability to “hedge their bets” by leaving larvae in northern ponds to over-winter, while the adults migrate. The same adults may not return, but can leave offspring in southern ponds that will eventually re-colonize northern areas. Monarchs do a similar thing by migrating as they breed, allowing subsequent generations to reach their destinations.
As I gradually learn the common dragonflies of our area, I am sometimes able to pick out new species as they arrive during migration or emerge from larval development. My most exciting find lately has been the discovery of a common migrant that can easily be overlooked. This is the wandering glider (see photo of a male from one of our ponds) or the globe skimmer as it is sometimes called. Here is a common species not only only across the US but around the world, It is the most widespread dragonfly and is capable of amazing migratory flights. The following website gives some information about the unique migration of Pacific poplations of this dragonfly some 11,000 miles across the Indian Ocean from India to Africa ( http://migrantwatch.in/blog/tag/globe-skimmer/ ). A link to a scientific paper by Charles Anderson is included; his story is quite interesting since he was a marine biologist in the Maldive Islands south of India and noticed these seasonal flights of globe skimmers as they passed through on the way to Africa. No one had imagined that dragonflies were capable of flying more than 10,000 miles during migration. I have also attached a map that shows this migration which occurs with subsequent generations of individuals. So here we can observe the most spectacular insect migrant known in all the world right in our backyards. It is however not so easy to identify as a monarch butterfly and thus has not received the attention that its spectacular natural history deserves.
The “odes,” odonates, or dragonflies and damselflies are a remarkable group of predatory insects that are beautiful, important ecologically, and amazingly interesting. A little bit of knowledge will enable you to identify some of the more common species and begin to observe their behavior and enjoy insights into their incredible world. This does not require years of study- just learn 5-10 common types and start from there.
Bill Dunson, Englewood, FL & Galax, VA