Mike Powell

On Wednesday I spotted a small group of a half-dozen of so Common Green Darner dragonflies (Anax junius) patrolling over a large field at Occoquan Bay National Wildlife Refuge. Common Green Darners are one of few species of dragonflies that migrate. Perhaps the ones that I saw are preparing to migrate from the local area or are just stopping off on their journey southward.

It is a fun challenge to point your camera toward the sky and to try and capture photos of these colorful dragonflies as they zoom overhead. The first image is the sharpest image that I was able to capture and it provides a good look at the dragonfly. In many ways, though, I am even happier with the second and third image that include some vegetation and help to provide some context to the shots.

The migration cycle of the Common Green Darner involves three generations. I highly recommend a research article entitled “Tracking dragons: stable isotopes reveal the annual cycle of a long-distance migratory insect” that was published in 2018 in the journal Biology Letters that explains the migration cycle and has some fascinating maps and diagrams. Despite the geeky-sounding title, it is actually quite easy to read and understand.

Here is an extract from the abstract for the article, in case you do not want to read the entire article:

“Using stable-hydrogen isotope analysis of 852 wing samples from eight countries spanning 140 years, combined with 21 years of citizen science data, we determined the full annual cycle of a large migratory dragonfly, the common green darner (Anax junius). We demonstrate that darners undertake complex long-distance annual migrations governed largely by temperature that involve at least three generations. In spring, the first generation makes a long-distance northbound movement (further than 650 km) from southern to northern range limits, lays eggs and dies. A second generation emerges and returns south (further than 680 km), where they lay eggs and die. Finally, a third resident generation emerges, reproducing locally and giving rise to the cohort that migrates north the following spring. Since migration timing and nymph development are highly dependent on temperature, continued climate change could lead to fundamental changes in the biology for this and similar migratory insects.”

Wow!

© Michael Q. Powell. All rights reserved.

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