Dragonfly Migration

By Scott Fitzpatrick on Friday, September 22, 2006.

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Birds aren't the only ones migrating south each year.

Hi. This is Scott Fitzpatrick from New Hampshire Audubon, bringing you Something Wild.

When we think of fall migration, we immediately think of birds. However, certain dragonflies journey south for the winter too.

But unlike birds, which fly back and forth in a single year, some dragonflies actually need two generations to complete a round trip.

Dragonfly migration occurs between late July and mid October, and peaks in September. Sometimes the insects travel in spectacular mass flights that can involve thousands or even millions of glittering individuals.

The largest swarms often follow the passage of cold fronts, when the wind comes from the northwest. They usually travel along seacoasts and lake shores, where there are abundant and tasty mosquitoes to snack on.

There are about four hundred known dragonfly species in North America, but only a few dozen of those are believed to migrate. Each fall, they travel from the northern United States and southern Canada, to the southern United States, the Caribbean and Mexico.

The best known, and most often studied, of these is the green darner. Two different populations of green darners live in Canada and the United States. The resident population does not migrate. They breed in the north over the summer and lay their eggs in water. The young, or nymphs, spend the winter in the chilly water beneath the ice. In spring, they emerge from the water, spend the summer as adults, and breed.

But the other population of green darners does migrate. In spring, they fly north and mate. The young emerge in late summer and by fall, they head south and breed. In this way, each generation alternates the direction of migration, so it takes two generations to complete a round trip.

So why do dragonflies migrate while others stay put? Scientists are trying to learn why, but for now it remains one of nature's great mysteries.

For Something Wild, I'm Scott Fitzpatrick.

Something Wild is a joint production of New Hampshire Audubon, New Hampshire Public Radio and the Society for the Protection of New Hampshire Forests.