Boyeria grafiana Williamson, 1907
Basis for Listing
The Ocellated Darner (Boyeria grafiana) is distributed throughout much of eastern North America but is either rare or does not occur any of the states and provinces surrounding Minnesota. Its Minnesota occurrences are at the westernmost limit of its continental range. Recent records of Ocellated Darners in the state have come from only the three counties of the northeastern Arrowhead region (Northern Superior Uplands Section). There is also one 1920 record (Odonata Central 2017) from Carlton County (Western Superior Uplands Section).
Ocellated Darner larvae require cold, clear, shallow, rocky, fast-flowing waters, and in some parts of their range, they are exclusively found in such streams shaded by a tree canopy. Based on the few isolated populations of this species encountered in Minnesota and their specific and pristine habitat needs, the Ocellated Darner was listed as special concern in 2013.
The Ocellated Darner is a richly colored medium-brown species, with 2 oval yellow dots on each side of the thorax and yellow smudges on the sides of the abdominal segments. Markings on the front of the thorax just behind the head are green to blue-green.
This species is very similar in appearance to the more common Fawn Darner (Boyeria vinosa) and care must be taken with their differentiation. The Ocellated Darner has oval yellow spots on the side of the thorax, while the Fawn Darner’s spots are round. Yellow smudges on the sides of the abdomen are larger in the Ocellated, and the Ocellated has little or no brown at the bases of the wings, as opposed to the distinct brown patches on Fawn Darner wings.
Although females are rarely encountered, the cerci (terminal abdominal appendages) of the Ocellated are short, about as long as segment 10. Female Fawn Darner cerci are notably longer, as long or longer than segment 9 (Paulson 2012; Dunkle, 2000).
Although in the eastern part of the Ocellated Darner’s range it is commonly known to breed along the shorelines of large cool, rocky oligotrophic (nutrient poor and oxygen rich) lakes, the Minnesota occurences of Ocellated Darner are all from classic North Shore tributaries, with swift current, high gradient, and rock substrate.
Biology / Life History
Preferring cooler conditions, the Ocellated Darner is most active later in the evening and also on cooler days; accordingly species in this genus in Britain are commonly known as “specters”. Adults shelter in heavily shaded forests during the heat of the day, venturing out in the open as the temperature drops. Males patrol just above the water and tight to the edge of the stream (Walker 1958). Little is known about the egg-laying habits of this species, and it is thought that oviposition occurs after dark (Walker 1958). The flight period of the Occelated Darner in Minnesota is early to mid-July through early October. Adults are indiscriminate feeders of flying insects. Very little is known about this species' larval life cycles or habits.
Conservation / Management
Threats to the Ocellated Darner in Minnesota include any land use activity that changes the hydrology of habitat or increases erosion or run-off within the watershed, as this increases the potential for siltation of the breeding waters. Because adult Ocellated Darners prefer shaded forests for feeding during the day, activities that would open up the canopy must also be avoided. Potential metal mining projects throughout this region could also have a major deleterious impact on the waters on which the species depends, including acidification of the waters and changes to the hydrogeology of the region.
Conservation Efforts in Minnesota
The non-profit Minnesota Dragonfly Society is looking for Ocellated Darners (among many other species of Odonata) throughout Minnesota through surveys and educational workshops. These surveys are conducted by volunteers and are supported through an Enbridge Ecofootprint Grant through 2018.
Kurt Mead, (MNDNR), 2018
(Note: all content ©MNDNR)
References and Additional Information
Abbott, J. C. 2006-2017. Odonata Central: An online resource for the distribution and identification of Odonata [web application]. <http://www.odonatacentral.org>. Accessed 21 March 2017.
Dunkle, S. 2000. Dragonflies through binoculars: a field guide to dragonflies of North America. Oxford University Press, New York, New York. 266 pp.
Legler, K., D. Legler, and D. Westover. 2013. Dragonflies of Wisconsin-Edition 5.1, copyright Karl Legler, self-published.
Mead, K. 2009. Dragonflies of the North Woods (North Woods naturalist series). Second edition. Kollath-Stensaas Publishing, Duluth, Minnesota. 200 pp.
Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.
Paulson, D. 2012. Dragonflies and damselflies of the east (Princeton field guides). Princeton University Press, Princeton, New Jersey. 544 pp.
Walker, E. M. 1958. The Odonata of Canada and Alaska : Anisoptera. Volume 2. University of Toronto Press, Toronta, Ontario, Canada. 330 pp.