The mosaic darners of the genus Aeshna (aka blue darners) are large, strong-flying dragonflies with late-season flight periods. Most are similar to each other in size and general coloration, so in-hand examination is usually necessary to identify them. The most important distinguishing characteristics for this genus are the shapes and colors of the pale stripes on the sides of the thorax, especially the first or anterior stripes (here referred to as anterior thoracic side stripes [ATSS]), and the shapes of the cerci (upper pair of claspers) at the tip of the abdomen (whether paddle type or wedge type). Other marks that are often helpful include the presence/absence of a black line across the face, and the sizes of the pale spots on top of the abdominal segments (S), including the presence/absence of a spot on S10. Refer to the images of Aeshna species on the species pages of this website to compare shapes of thoracic side stripes and consult any dragonfly field guide for illustrations of the claspers (some guides are listed in the Resources Section).
Males are readily separated from other darners by the combination of deeply notched anterior thoracic side stripes, no black line across the face (similar lake darner has black face stripe) and small bumps on top of the cerci near the tip of their paddle-type claspers (similar green-striped darner lacks fine bumps there, but magnification is needed to see if bumps are present). In Wisconsin, thoracic side stripes of Canada darner are usually mostly blue, but often with some green at their lower ends; Green-striped darner thoracic side stripes are usually all green. Females have thoracic side stripes either all green or mostly blue like males. Those with green stripes are very similar to female Green-striped darner. Separating females of the two species is not easy, and isn’t always feasible, but marks on the side of the thorax and base of the abdomen can be helpful.†
This species is common throughout southern Canada and the northern United States, and it is common throughout Wisconsin. Typical habitat includes bog-bordered lakes, boggy ponds, fens, and slow streams. Canada darners may be observed in feeding swarms with other mosaic darners in upland clearings, especially at dusk. It is probably the most common mosaic darner in the northern half of Wisconsin.
Late May to early October, relatively early for an Aeshna. Prime time is July and August.