11 June 2024

New state record: Great Pondhawk

David Marvin collected a Great Pondhawk (Erythemis vesiculosa) in Ingham County on 9 June 2024, a first state record for Michigan. Although patterned like the female or young male common Eastern Pondhawk (Erythemis simplicicollis), it is larger (closer to a Common Green Darner, Anax junius) with a longer, much more slender abdomen. The hindwing of an Eastern Pondhawk is 30-33 mm, with a hindwing of >38 mm immediately keying to Great Pondhawk in Needham et al. (2014). The Michigan individual has a hindwing measurement of 42 mm. The other portion of the key's couplet (and a diagnostic character in Palacino-Rodríguez et al. 2014) indicates Great Pondhawk has a double row of cells in a particular area of the forewing, which I've pointed to below. Eastern Pondhawks have a single row in this location.

As depicted in David's photo at the top of the post, Great Pondhawks will also perch more often on vegetation rather than on the ground like Eastern Pondhawks. Great Pondhawks are described as agile, aggressive, and apt to patrol more like a darner. It wouldn't be too hard to pass them off as darners or Eastern Pondhawks without a closer look, and in fact some of the extralimital records initially puzzled or surprised the observers, or were discovered "after the fact" from photos.

Erythemis is a largely Neotropical genus. Great Pondhawk ranges from Argentina through Central America and Mexico into the southern and southwestern United States. In the US, it is most common in Texas and south Florida. Occasionally, especially in the past decade, vagrants have been sighted farther north, with more records from Oklahoma, Kansas, and Tennessee. This map is from Odonata Central.

Zooming in on the Upper Midwest, one sees that all the records north of approximately 40.6 N (the southern border of Iowa) have occurred since June 2020. With the exception of the Michigan record, all are sight records only.

There are no records from Wisconsin, Indiana, Kentucky, Ohio, New York, or Pennsylvania. The two eastern records are south of 40 N, from Arlington Co., VA (2018) and Garrett Co., MD (2023). A number of lists indicate Great Pondhawk has occurred in Missouri, but I've not yet located a source.

As is often the case when southern lentic odonate species move north, there is a lot of speculation on how environmental conditions prompt these movements, especially in light of climate change. We've addressed this issue in two previous papers on southern species we found in the state:

Craves, J.A. and D.S. O’Brien. 2007. Erythrodiplax umbrata (Odonata: Libellulidae): New for Michigan. Great Lakes Entomologist 40:96-98.

Craves, J.A. and D.S. O’Brien. 2011. Tramea calverti (Odonata: Libellulidae): new for Michigan with notes on other new reports from the Great Lakes region. Great Lakes Entomologist 44:78-82

Thus it is significant that this Michigan voucher is the northernmost I have located thus far. The next closest is from Leavenworth Co., KS from 1936, which is about 450 km south of Ingham Co., MI. 

We will again be working with Dr. Anthony Cognato at Michigan State University to use DNA analysis to see if we can determine the population origin of this individual by comparing genetic markers with other Great Pondhawks from Florida and Texas, for example. This may be able to help us connect environmental conditions such as drought in a particular region as a trigger for dispersal.

I want to note that we cannot conclude that this individual came directly from a southern population, however. Great Pondhawks fly nearly year-round in tropical latitudes and much of Texas, with a peak in late summer and fall. With over 50 records, mostly after 2006, Oklahoma dates range from 2 April to 11 August (Smith and Patten 2021). Further north, discerning true flight periods is more difficult, because we don't know whether they are dispersing from somewhere distant, or recently emerged from a closer locale. In  his book Dragonflies and Damselflies of Texas and the South-Central United States, John Abbott notes that the pseudostigmas of "young" individual Great Pondhawks are green. Here is the Michigan individual:

While I have yet to research the timing of color change in the pseudostigma, perhaps the green color and the relatively fresh appearance of the Michigan individual may suggest it did not travel hundreds of kilometers prior to its Michigan arrival, but came from a closer breeding population. Another molecular technique, stable isotope analysis, could help us greatly narrow down the latitude where this individual emerged. This can offer further insight into the population dynamics of this species, whether we determine that it made an impressive long-distance movement from a distant region, perhaps due to weather or environmental conditions, or came from a pioneer breeding population further north. 

We are often asked why we put so much emphasis on (targeted) collecting. The issues discussed here point out the value of specimens in providing answers to questions far beyond just the confirmation of identity, with implications crucial to invertebrate conservation. This specimen will be deposited in the Michigan State University Albert J. Cook Arthropod Research Collection, where we are adjunct curators of Odonata.

I can't say that this addition to the Michigan list surprised me. In fact, just hours before David's text to us about his find, Darrin and I were talking about the potential to find Great Pondhawk in Michigan -- I even had a little file that I started a few years ago when they began to pop up in the region. But, it's early days and there is further background research to do. We will be working on a paper for submission to a journal once we map out a plan and execute lab analyses. Congrats again to our friend David!

Literature noted

Abbott JC (2005) Dragonflies and Damselflies of Texas and the South-Central United States. Princeton University Press, Princeton.
Needham JG, Westfall MJJ, May ML (2014) Dragonflies of North America. Third Edition. Scientific Publishers, Gainesville, FL.
Palacino-Rodríguez F, González-Soriano E, Sarmiento CE (2014) Phylogenetic Signal of Subsets of Morphological Characters: A Case Study in the Genus Erythemis (Anisoptera: Libellulidae). Caldasia 36(1):85-106.

Smith BD, Patten MA (2021) Dragonflies at a Biogeographical Crossroads, the Odonata of Oklahoma and Complexities Beyond its Borders. CRC Press, Boca Raton, London, New York.