Western Great Lakes Bird & Bat Observatory

Headquarters at Forest Beach Migratory Preserve

Southeastern Wisconsin Conservation Summit

CRITICALLY IMPERILED DRAGONFLY SPECIES AT FBMP

by Freda van den Broek (Vice President, Wisconsin Dragonfly Society)

The Critically Imperiled Spatterdock Darner Dragonfly (Rhionaeschna mutata) has been observed at Forest Beach Migratory Preserve for the third consecutive year.

While it would require some knowledge of the Odonata (the dragonflies and damselflies) of Wisconsin to know that one was seeing a very rare dragonfly (Legler, 2013), it wouldn’t take more than an appreciative eye to know that the dragonfly in question was something special. At three inches in length, the average Spatterdock Darner is roughly equivalent in size to the most commonly seen large dragonfly at the pond, the Common Green Darner (Anax junius). However, its bright blue eyes, its black and blue body, and its breathtaking agility make it easily distinguishable from most other dragonflies -- that is, except for the Blue-eyed Darner (Rhionaescha multicolor), the only other member of the Rhionaeschna genus that has ever been recorded in Wisconsin.

It generally requires hand examination to distinguish the Spatterdock Darner from the Blue-eyed Darner (R. multicolor), as the physical differences (body length and clasper shape) are very subtle. When this dragonfly was first photographed at Forest Beach Migratory Preserve in 2015, Wisconsin’s Odonata expert, aquatic ecologist and author Robert DuBois, was able to confirm the identity on the basis of an in-flight photograph. It was the first record of the species for Ozaukee County, one of only a handful of records for all of Wisconsin. In 2016, a specimen was netted and its identity was confirmed by physical examination. At present, the Spatterdock Darner has S1 conservation status in Wisconsin, meaning that it is critically imperiled due to a very restricted range, very few populations or occurrences, very steep declines, severe threats, or other factors.”  

DuBois and others documented the historic records for the Spatterdock and Blue-eyed Darners in Minnesota and Wisconsin and their overlapping ranges in an article published in ARGIA (the news journal of the Dragonfly Society of the Americas) in 2015. Since the first Wisconsin sighting in Marquette County in June 1989, the Spatterdock Darner has been recorded at only a handful of other sites in Waukesha and Walworth Counties. Owing to habitat changes at the site in Marquette County, Spatterdock Darners have not been recorded there in recent years. For the 2017 flight season, only two Wisconsin Odonata Survey records for the Spatterdock Darner exist: one from Waukesha County and a couple from Forest Beach Migratory Preserve in Ozaukee County.

What could possibly make Forest Beach Migratory Preserve suitable habitat for a critically imperiled dragonfly? This question has yet to be answered. In terms of its historically known habitat, the Spatterdock Darner is said to prefer shallow ponds with an abundance of spatterdock plants (water lilies of the Nuphur genus), the absence of centrarchid fishes, and a mostly forested landscape. The Clubhouse Pond fits only one of these conditions: it is relatively shallow. There are no water lilies, the presence of fish has been confirmed, and the surrounding landscape is predominantly prairie.  

It would appear that the Spatterdock Darner’s future at Forest Beach Migratory Preserve hangs in a precarious balance. Time will tell whether environmental challenges, including the existence of a successful breeding colony of Purple Martins (predators of flying insects, including rare dragonflies) in the immediate vicinity of the Clubhouse Pond will sufficiently suppress the fragile Spatterdock Darner population so as to relegate it to the status of historical record. A preferred vision of the seasons to come holds many visitors from far and wide, delighting in the glimpse of this beautiful, not-so-rare dragonfly.   

References

DuBois, R; Lawrenz, R; Johnson, D; Smith, W; Chrouser, R and Jackson, D 2015. First records for Rhionaescha multicolor (Blue-eyed Darner) and R. mutata (Spatterdock Darner) in Minnesota and Wisconsin, and Their Overlapping Ranges in These States. ARGIA 27(3): 15. Legler, Karl and Dorothy with Westover, Dave. 2013 (Edition 5.1). Dragonflies of Wisconsin  

Website Consulted

Wisconsin Odonata Survey http://wiatri.net/inventory/odonata/ http://wiatri.net/inventory/odonata/SpeciesAccounts/SpeciesDetail.cfm?TaxaID=6