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).
Both genders are readily distinguished from other mosaic darners by the shape of the anterior thoracic side stripes (ATSS), which are bent slightly forward in the upper half. Thin, pale lines are usually visible between and in front of the side ATSS. There is a moderately thick black line across the face. The eyes appear more greenish, less bluish, than most other mosaic darners. Males have paddle-type claspers. Females may be blue form, green form, or yellow form.
Ranging throughout Canada and northernmost United States, this species can be found at bog ponds, deep fens with well-defined edges, and northern swamps with abundant Sphagnum and other mosses. It occurs in Wisconsin at a handful of sites in a cluster of northern counties.
Throughout its range, the flight season is from early June to early October. In Douglas County, Wisconsin, most adults are seen in late August and early September.