The bluets form a group of about 17 similar species in Wisconsin in which the males usually share the characteristics of having blue and black stripes on the thorax, and blue and black markings on the abdomen. In-hand examinations are usually needed to identify them, although they can be grouped into subcategories based on the amount of black showing on the abdomen. Males are easily identified, under magnification, by the shape of their terminal appendages. Females are generally duller than males, and they are more difficult to identify, which is accomplished by subtle differences in the shape of the mesostigmal plates on the top of the thorax. Generally, males are bright blue while the females are green or yellow-green or blue. There are some species that are yellow-orange, a mix of various colors, or black with some blue.
The males of this species can exhibit either blue-type or intermediate-type amounts of blue on the abdomen. It is very similar to the marsh bluet, differing by the shape of the terminal appendages. The bluet's length varies from 1.1 to 1.3 inches. The male has a blue thorax with black dorsal and shoulder stripes. The female's thorax is similar but the pale areas are light brown to bluish or green. Her abdomen is black dorsally.
Found throughout northern United States and southern Canada, Hagen's bluet is usually found in ponds, marshes, open bogs, lakeshores, and slow streams. It is tolerant of acidic waters. It is common and widespread throughout Wisconsin.
Early June to early September in Wisconsin.