Wednesday, May 26, 2010

The invasion of the Common Green Darner

[all photos taken at Marathon on May 25 - click images to enlarge]

The Common Green Darner (Anax junius) is a conspicuous and abundant dragonfly throughout its North American range. Its life history parallels that of the Monarch Butterfly: adults migrate north each spring from wintering areas in Central America and the southern U.S. Upon arrival in the Great Lakes region they mate and lay eggs. The larvae mature over the coming months and emerge as adults before migrating south en masse in the early autumn. In southern Ontario, there is a resident life history variant with over-wintering larvae which emerge in late May. Mead (2003) speculated that a resident population may also occur in the upper Great Lakes states.

Despite its familiarity to many dragonfly enthusiasts, it is not well known from northwest Ontario. Until this spring, there were only four occurrences (the first in 1913) documented for the Thunder Bay District. On June 30, 2000, Mike Oldham observed more than 20 individuals on the wing over a marsh along the Arrow River near the Minnesota border. The other three sightings, the last in 2005, were of single individuals, presumed strays, near the Lake Superior coast.

So it came as a surprise to us when we encountered a male foraging along a road near Prairie Cove on April 10. A month later we photographed a female near the administration building at Pukaskwa. During the May 15-16 Dorion's Canyon County Bird Festival we saw several more over the marsh at Hurkett Cove (where someone observed one being captured by an American Kestrel) and a singleton at Ouimet Canyon Provincial Park, our furthest inland sighting so far. That same weekend Al Harris told us that he had seen scores of Common Green Darners between Thunder Bay and Nipigon this spring.

The plot thickened yesterday when I visited a beaver pond on the mill property beside Peninsula Harbour. The hot weather had triggered an emergence of several resident dragonfly species. Four-spotted Skimmer, American Emerald and Beaverpond Baskettail were mating and/or ovipositing along the pond edge. More numerous where the Common Green Darners. After tallying a dozen or so males flying over the pond, I flushed a mating pair from the grass and then saw several more pairs flying in tandem along the shore. One pair landed on a floating cattail stem where the female began ovipositing. Over the course of the next half hour, I observed nine more (guarded) females laying eggs on decaying, floating cattail stems! For those of us who really like dragonflies, this is great stuff.

I suspect that yesterday, Common Green Darners were mating and laying in wetlands across the north shore, and perhaps in adjacent regions where breeding hasn't previously been documented. All of this raises some intriguing questions. Is this phenomenon restricted to the Lake Superior coast? Just what triggered this apparent invasion?

One possibility is that northbound Common Green Darners reached their traditional breeding areas in northern Wisconsin, Minnesota and Michigan this spring only to find dessicated wetlands. Recent data from the U.S. Drought Monitor reveal abnormally dry to severe drought conditions in the region. With the associated reduction in available breeding habitat, perhaps tens of thousands of Common Green Darners continued to migrate north into (and perhaps beyond) our area. If this is the case, we might expect more sightings well north of Lake Superior as the north shore is similarly parched.

Have you seen Common Green Darners in your area this spring?

Of related interest

I noted in an earlier post that observing and documenting dragonflies and damselflies in Ontario became much easier with the publication of A Field Guide to The Dragonflies and Damselflies of Algonquin Park. This beautifully illustrated, very easy-to-use guide covers all of the species one might expect in our area. Also of interest to those of us in northwest Ontario are a couple of more recent items.
  • The most recent issue of ON Nature magazine featured a great article, The Tiny Hunter, which documents the growing interest in the odonate fauna of Ontario. The piece appropriately recognizes the pioneering scientific work of Edmund Morton Walker who made extensive collections of odonata in the Nipigon basin in the years following the First World War. It's a great read.
  • Rob Foster and others have compiled an annotated checklist of the dragonflies (63 species) and damselflies (19 species) of the Thunder Bay District. An accompanying map reveals the Thunder Bay District to be a largely unexplored frontier. Undoubtedly, the checklist will help encourage more interest in these fascinating creatures.


Dubois, R. 2005. Damselflies of the North Woods. Kollath-Stensaas Publishing, Duluth, MN. (available here).

Foster, R.F., Elder, D.R. and A.G. Harris. 2010. Checklist of the Dragonflies and Damselflies of Thunder Bay District, Ontario. Thunder Bay Field Naturalists (on-line).

Jones, C.D., Kingsley, A., Burke, P, and M. Holder. 2008. Field Guide to The Dragonflies and Damselflies of Algonquin Provincial Park and the Surrounding Area. The Friends of Algonquin Park.Whitney, Ontario (available here).

Lam, E. 2004. Damselflies of the Northeast. Biodiversity Books. Forest Hills, New York (available here).

Mead, K. 2003. Dragonflies of the North Woods. Kollath-Stensaas Publishing, Duluth, MN. (available here).

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