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).
There are at least three subspecies of variable darner in North America, with two subspecies in Wisconsin. Both are distinguished by the shape of the anterior thoracic side stripe (ATSS) in combination with thoracic top stripes that are small or absent and a thin black line across the face. The interrupta form has an incomplete ATSS that is divided into two dots. The lineata form has a complete but narrow ATSS that is straight but may be irregularly widened at the ends. Because the side and top stripes are reduced on this species, the thorax appears darker, even in flight, than other mosaic darners. Males have paddle-type claspers.
Description of Habitat/Range:
This species occurs in most of Canada and the northern United States. It is found at a variety of wetlands including boggy ponds, lakes, fens, slow streams, and sloughs. Often flies in uplands and hilltops, and regularly joins other mosaic darners in mixed species feeding swarms. It may be abundant in prairie ponds and open habitats dominated by sedges or cattails. Most Wisconsin records are from the northern half of the state.