Identifying Mosaic Darners (Aeshnas) in MD
Mosaic Darners, genus Aeshna, are large, strikingly beautiful dragonflies of primarily northern distribution. They are characterized by their intricate patterns of blue to green to yellow. Five species are regularly found in MD, but only the Shadow Darner, Aeshna umbrosa, is widespread. They are very active fliers, rarely seen perched. They usually perch high in trees. Consequently, they are very difficult to ID in the field. They are best identified in the hand by details of the terminal appendages, well illustrated Needham, Westfall, and May. Click here for my drawings of appendages for the males of some northeastern species. Illustrations for the females are found in The Odonata of Canada and Alaska, vol2,by E. M. Walker. They also differ in the precise details of their colorful markings, and usually can be identified by pattern with a little practice, assuming you can find one perched in good light.
Identification in flight with binoculars is very challenging. Since the males often patrol at eye level, and sometimes hover, you can occasionally clinch an identification in flight. The single most useful feature is the exact shape and color of the lateral thoracic stripes under the wing. Most such sightings are best left as tentative. Location is also a good clue, but keep in mind that distribution knowledge in MD is incomplete. Preferred habitat for all species is beaver ponds, marshy edges of larger ponds, and sometimes streams. Since they rely on habitats that are sometimes temporary, there seems to be some dispersal, and they can turn up just about anywhere. However, they are rare away from breeding sites. Differences in the flight style of the males are mentioned below, but all species can fly high when feeding.
The shapes of the markings are generally more useful than the color. Old males tend towards blue. Females may be either mostly blue-spotted, like the males, or green to yellow. Newly emerged of both sexes have dull yellowish markings. See the pictures under Green-striped Darner for sexing.
Canada Darner Aeshna canadensis Known only from beaver ponds in Garrett County, where it is often the commonest Aeshna. Closest in appearance to Green-striped Darner, separable in the hand by the terminal appendages , or the shape of the thoracic stripes. Males tend to patrol a few feet above the water, higher than Shadow Darner. Season is June-September, but rare before August. Mt Nebo WMA, Finzel, Garrett County.
|Comparison: Shadow, Green-striped and Canada Darners in flight|
Spatterdock Darner Aeshna mutata Males relatively easy to identify because of their screaming blue eyes and markings. Males tend to patrol higher than other species, except Black-tipped Darner. Normally the only Aeshna flying in May and June. The rarest regularly occurring Aeshna in MD. Known only from Mt Nebo, Garrett County, and a small pond at Patuxent NWR. Requires spatterdock and relatively fish-free ponds. Season is May-June. To be looked for in small ponds elsewhere.
Black-tipped Darner Aeshna tuberculifera Males are relatively more slender, and paler bluer. Males patrol higher than Canada and Shadow Darners. Uncommon and very local from Garrett to the Piedmont. May utilize small drainage ponds. Mt Nebo, Garrett Co, Pinto Marsh, Allegeny Co, Blair Valley Lake, Washington Co. Season is June to October, rare before August.
Shadow Darner Aeshna umbrosa In most places the only Aeshna. Found from Garrett to the edge of the coastal plain. May use small streams that are not very marshy, but most common around beaver ponds. Males are very slender, and patrol very low, just above the water, investigating every clump of vegetation. Both sexes have relatively smaller abdominal spots, and usually look very dark in flight. Season is June to November. Becomes common in the mountains in August, not until September or October at lower elevations. Active on sunny afternoons in early November.
Green-striped Darner Aeshna verticalis Uncommon In Garrett Co, at Blair Valley Lake in Washington Co, and formerly in Anne Arundel Co. Thoracic stripes greener or yellower than Canada Darner. Season is August to October.
Other Aeshnas: There is one record, location unknown, of Lance-tailed Darner, Aeshna constricta for MD. Males are rather bright blue, like Spatterdock or Black-tipped, with terminal appendages like Shadow. To be looked for in the the piedmont and ridge and valley sections, September-October. There is a possible record of Lake Darner, Aeshna eremita. Males and some females have very dark blue markings and are very large. Mottled Darner, Aeshna clepsydra, with a very intricate thorax pattern, has strayed once to southern NJ.