Wednesday, September 23, 2009

Are Dragonflies Disappearing this Year?

Lots of folks have commented to me this summer that they haven’t been seeing many dragonflies. Hm. I’ve seen lots of dragonflies (and damselflies) this year, and I haven’t been able to think of any reason why dragonflies would be sparse; after all, it was good and wet this year, so they had plenty of water for successful reproduction and growth. All the rain also meant a lot of habitat for mosquitoes and the other insects that make up their diet.

Maybe numbers were down in some locations because it was also a cool summer. Like all insects (that I know of), dragonflies need sunshine to get the blood moving (so to speak). This is why you see them basking in the sunshine. Just like people, when they get too chilled, they cannot move well, making them easy targets for other predators. Perhaps some of the species that we see in July and early August never got warm enough to successfully emerge as adults. I just don’t know.

I can tell, you, however, that September has been a great month for dragonflies. I’ve seen squadrons flying in formation over the streets and roads, phalanxes patrolling yards and parking lots, and down on the water the air has been filled with non-stop dragonfly action.

I’ve been very lucky this month to put my canoe on the water several times. This has put me smack in the middle of the action. Most prominent among the Odonates (the order of insects known as dragon- and damselflies) I’ve been seeing this fall are pairs of yellow-legged meadowhawks (Sympetrum vicinum) flying around in their mating embrace.

As with all dragonflies, when the male encounters a likely female, he grasps her by the head. It sounds worse than it really is. The male uses a special grasper at the tip of his abdomen (tail) to grab the female just behind her enormous eyes. They are now flying in tandem. The female then bends her abdomen around to receive the sperm packet from the male. You’ve probably seen pairs of dragonflies in this loop formation; now you know what’s going on.

Sometimes after fertilization the female lays eggs with the male still attached to her head. Other times the male flies away, his work finished, and the female, who can store sperm for a very long time, eventually lays her eggs on her own. If you see a dragonfly flying along and repeatedly tapping its abdomen to the water, that is what she’s doing.

The eggs eventually hatch, and the emerging nymph begins its life in the water, where it is a major predator of other aquatic invertebrates. Depending on the species, dragonflies remain in the nymph stage anywhere from one month to five years! As they grow, they molt, just like caterpillars and other larvae. Eventually, however, they emerge from the water for a final molt, in which they transform (metamorphose) into their adult forms.

One of the latest dragonflies of the season around here is the large common green darner (Anax junius). It is the first to appear in the spring, and often the last to disappear in the fall. If you find yourself in need of a dragonfly fix, get down to your nearest wetland and have a seat. A little patience is all you need, and before long you will see these flying wonders zipping and zooming all around.

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Ellen Rathbone is by her own admission a "certified nature nut." She began contributing to the Adirondack Almanack while living in Newcomb, when she was an environmental educator for the Adirondack Park Agency's Visitor Interpretive Centers for nearly ten years.

Ellen graduated from SUNY ESF in 1988 with a BS in forestry and biology and has worked as a naturalist in New York, New Jersey, and Vermont.

In 2010 her work took her to Michigan, where she currently resides and serves as Education Director of the Dahlem Conservancy just outside Jackson, Michigan.

She also writes her own blog about her Michigan adventures.



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