Common Green Darner (Anax junius), Black River State Park, Jackson County, Wisconsin. (2017) Copyright Ken Tennessen.
November Species of the Month: Common Green Darner (Anax junius)
DSA’s November “Species of the Month” is the Common Green Darner (Anax junius) in the family Aeshnidae. It is a migratory species, 68-78 mm in length (about two and a half to three inches), and is found throughout most of the United States north into Canada and south into Mexico and Central America, as well as many other parts of the world. Its preferred habitat is lakes, ponds, or small streams but the Common Green Darner can be seen almost anywhere. Join Ode expert Ken Tennessen as he recounts an unusual experience with this migratory species.
Ode To An Unusual Feast
A frenzy of Anax junius (Common Green Darners) bedazzled my hometown of Wautoma in Waushara County, Wisconsin. They appeared along east Mt. Morris Street (lat/long 44.0757, -89.2873)) in the late afternoon of September 20, 2024. I first noticed them a little after 6 p.m., but there were already lots of them, so the activity had started before that.
Common Green Darner (Anax junius), Sandhill Wildlife Management Area, Wood County, Wisconsin. (2006) Copyright Ken Tennessen.
With no way to count them, I estimated that hundreds were zipping about, flying fast and low, for several blocks as far as I could see. Temperature was 78 degrees Fahrenheit and relative humidity was 53 percent.
Common Green Darner (Anax junius), The Morton Arboretum, Lisle, Illinois. (9-5-20) Copyright Cindy Crosby
Silhouetted against the sun, I could see a variety of small insects flying above the lawns, but I think the Common Green Darners were concentrating on the winged ants that must have been dispersing from some gallery in the neighborhood. I soon deduced that the dragonflies must be eating just the abdomens of the ants, as I found dozens of partial bodies on the sidewalk. Only the head, thorax, and wings remained. The mutilated ants were still alive and crawling frantically but with the abdomen missing (Fig. 1) they could no longer fly.
Remains of citronella ants (Lasius sp.) found crawling on the sidewalk without their abdomens, after being attacked by Anax junius; Wautoma, Wisconsin. (9-20-24) Copyright Ken Tennessen.
P.J. Liesch of the Insect Diagnostic Lab at the University of Wisconsin confirmed the prey to be citronella ants in the genus Lasius. I found one report of adult Anax junius feeding on ants, by Warren (1915), who studied this species feeding in Hawaii; however, he did not identify any specific type of ant. My observations may constitute the first specific report of dragonflies feeding on citronella ants. Lasius belongs to the subfamily Formicinae (Boudinot et al. 2022), so apparently they produce formic acid. How much acid these ants produce is questionable, but it appears it did not deter the dragonflies from ingesting them. Formic acid is produced in the gaster (abdomen). So, that is what the “CGDs” were eating!
Common Green Darner (Anax junius), The Morton Arboretum, Lisle, Illinois. (7-9-21) Copyright Cindy Crosby.
Easy to recognize, the Common Green Darner has a distinctive black "bulls eye" mark on its head, in front of the huge eyes. Males have a green thorax but are largely blue on the abdomen, whereas females are green and rusty brown. The female often oviposits in tandem with the male but also lays eggs alone.
Common Green Darners (Anax junius), Nachusa Grasslands, Franklin Grove, Illinois. (6-9-24) Copyright Cindy Crosby.
This species is known to migrate long distances, feeding voraciously on other insects, storing fat and protein. They show up in Wisconsin in early spring when it is still quite cold and before the resident population emerges. Our spring migrants come from points far south; in the fall, the next generation heads south. Much has yet to be learned about their migratory routes and life history traits.
Around 6:30 p.m., with the sun near the horizon, the number of Common Green Darners decreased abruptly, and shortly afterwards I saw only a few individuals. They left me with questions. Where did they go? Will they show up again tomorrow? If not, where are they going? How did they form the swarm and find the winged ants?
The only answer I can offer is, no, they did not show up the next day.
References
Boudinot, B. E., M. L. Borowiec, and M. M. Prebus. 2022. Phylogeny, evolution, and classification of the ant genus Lasius, the tribe Lasiini and the subfamily Formicinae (Hymenoptera: Formididae). Systematic Entomology 47: 113–151.
Warren, A. 1915. A study of the food habits of the Hawaiian dragonflies. Bulletin, College Hawaii Publications 3: 4–45.
May, M. L., J. H. Matthews. 2008. Migration in Odonata: A case study of Anax junius. Pp 63–77 in Cordoba-Aguilar, A., (ed.) Dragonflies, model organisms for ecological and evolutionary research. Oxford University Press, Oxford.
More Migration Information
May, M. 2013. A critical overview of progress in studies of migration of dragonflies (Odonata: Anisoptera), with emphasis on North America. Journal of Insect Conservation 17:1–15.
C. Scott Clem and Joseph V. McHugh "Documentation of Diurnal and Nocturnal Migratory Activity of the Dragonfly Anax junius (Odonata: Aeshnidae) on Sapelo Island, Georgia, USA," Southeastern Naturalist 23(3), N54-N57, (7 October 2024). https://doi.org/10.1656/058.023.0316
Russell, R. W., M. L. May, K. L. Soltesz, J. W. Fitzpatrick. 1998. Massive swarm migrations of dragonflies (Odonata) in Eastern North America. American Midland Naturalist 140:325–342.
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Ken Tennessen has studied dragonflies for over 50 years, publishing papers and books on their systematics, phylogeny, life cycle, behavior and conservation. A major work, Dragonfly Nymphs of North America, was published by Springer Nature in 2019. He has written numerous articles for DSA newsletters and has published over 80 technical papers in technical journals, including naming 22 new species of Odonata; four New World species are named for him. Email: tenkenneth43@gmail.com
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Editor’s note: This essay appeared in slightly different form first in Wisconsin Dragonfly Society’s Ode Notes September 2024. Introductory information is from Dennis Paulson’s Dragonflies and Damselflies of the East and Dragonflies and Damselflies of the West and other sources.
