If you’ve been lucky you may have had the surprising pleasure of happening upon a Common Green Darner (Anax junius) swarm in the late summer and early fall. Maybe you’ve been hiking through the prairie or even just sitting in your yard when suddenly, everywhere you look, there are dragonflies, skimming along the tops of the grasses.
When I think of migration, I have to admit, birds are the first group that come to mind, but as the Monarch Butterfly exemplifies, insects can also make spectacular migrations. The Common Green Darner may not be as showy as the large orange butterfly but they are equally as interesting and travel just as far.
The Common Green Darner is a very large dragonfly, up to 3 inches in length, which, as its name suggests, is a very common summer resident in Iowa and across the United States. They (and several other species) are called Darners because they are said to resemble darning needles. As adults, they are acrobatic flyers and voracious predators of other insects. As with all Odonates (Dragonflies and Damselflies) Green Darners start life in the water as a nymph, which is also predatory. Because of this important tie to water, adult Darners are most often found near wetlands, ponds and lakes but they can also be found quite far from water, particularly during migration.
Photo courtesy of U.S. Fish and Wildlife Service
One of the most interesting things about the Green Darner migration is that research suggests not all individuals do it! There are both migratory and resident individuals in Iowa and they approach life very differently. Year-round residents mate and lay eggs in the late summer and fall and their young then overwinter under water and don’t develop into adults until the middle of the next summer. Migrants on the other hand, arrive back north in the late spring, lay eggs in June and then become adults in August in time to head to Central America in late August and September. They are thought to go through their life cycle again in the south and the individuals which mosey back north are not the same individuals who migrated south. The northward migration in the spring is much less organized and large swarms are not as common as in the fall.
As with a lot of insects, we still have a lot to learn about these fascinating creatures and their migration patterns. What we do know, is that Green Darners play an important role in our wetland communities and that happening upon a swarm of them as they move slowly but steadily southward is an amazing experience. So get outside and have fun this fall hunting for this unique migrant!