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).
This large, dark-appearing darner is characterized by the combination of relatively straight anterior thoracic side stripes (ATSS) that are narrowly outlined in black, pale spots on top of the abdomen that are smaller than usual for mosaic darners (a western subspecies has larger spots on abdomen that are typical of most mosaic darners), and the male's wedge-type claspers. Location is also a useful clue – it is far more likely to be found along flowing waters in shaded areas than other mosaic darners. Similar lance-tipped darner males also have wedge-type claspers but have larger spots on the abdomen and ATSS that are slightly notched and lacking a black outline.
Description of Habitat/Range:
This species is common throughout much of Canada and the northern United States. It is common throughout Wisconsin. Preferred habitats are usually at least partially shaded, and include forested rivers and streams of all sizes, ponds, lakes, ditches, and marshes. It is the most common mosaic darner in flowing waters in Wisconsin. Often flies well into the evening.
Late June to late October in Wisconsin. One of latest dragonflies of the year in the north, with a flight period that extends well into the fall season.