In July 2011, I photographed a large Arigomphus dragonfly at Petrie Island. It had greenish eyes, a dark abdomen with rusty-coloured spots on the bottom of the last couple of segments, and an entirely yellow tenth segment. I only got two photos of the clubtail before it flew off, but the two angles showed that there was no black on the sides of the final abdominal segment. According to my research, only one species in Ontario has an entirely yellow tenth segment – the Unicorn Clubtail, a southern species that wasn’t even on the Ottawa checklist. Based on my photographs, which show the completely yellow tenth segment, a few of Ottawa’s most knowledgeable students of the odonata concluded that it could only be a Unicorn Clubtail – a new record for the region, and the 123rd species observed in the Ottawa area.
In July 2012, I was part of a team of dragon-hunters which went looking for this species at Petrie Island. The team included Bob Bracken, Chris Lewis, and Mike Tate. Bob and I spotted a large Arigomphus dragonfly, and I took one quick photo before he tried to net it. His attempt failed, and this photo is the only record we have of that 2012 clubtail. Again the image shows an entirely yellow tenth segment.
In June 2015, Chris Traynor and another member of the OFNC Facebook group photographed Arigomphus dragonflies with what appeared to be entirely yellow tenth abdominal segments west of Ottawa. It seemed strange for the Unicorn Clubtails to pop up suddenly in the west end, especially since there had been no Unicorn Clubtail sightings anywhere in the region since 2012. Chris Lewis, Chris Traynor and I decided to post our photos to the Northeast Odonata Faceboook Group, which includes many prominent members of the Dragonfly Society of the Americas, several professional writers, bloggers, and authors, and other really knowledgeable dragonfly enthusiasts who have been studying these insects a lot longer than Chris, Chris, and I have.
After studying the images I posted, Ed Lam, the author of Damselflies of the Northeast: A Guide to the Species of Eastern Canada & the Northeastern United States (2004), noted that the cerci (upper claspers of the terminal appendages) appear shorter than the epiproct (the lower appendage) in the photos, which supports the similar-looking Lilypad Clubtail (A. furcifer) rather than Unicorn Clubtail (A. villosipes). He then took the time to photograph these two species with the appendages in the exact same position as the ones in my photos. The resulting diagram he put together was conclusive:
Not only are the upper claspers shorter than the lower clasper, they are even the same shape with a heavy downward arch.
In the Facebook discussion, Chris Lewis responded with the comment that “structure rules again” – that is, structure is more important than colour or pattern when it comes to identifying odes. She also asked about the extensive pale yellow colour on the tenth segment of the two dragonflies I photographed. According to the Algonquin field guide and other online resources, the Lilypad Clubtail has only an elongated yellow spot on top of the tenth segment- the sides of the segment are very dark. She asked Ed if the extent of the paleness down the sides was variable in both species. Ed answered that in his experience, the amount of darkness on those last segments is variable on both Lilypad and Unicorn Clubtails.
So there it is – there are no Unicorn Clubtails in Ottawa (that we know of), and the next time someone spots a clubtail with an entirely yellow tenth segment, it’s best to check the shape and size of the claspers, as these are the most reliable field marks for identifying an odonate to species.
Author’s Note: Many thanks go to Ed Lam for the use of the image comparing the claspers of each species, and for his helpful comments on Northeast Odonata. Even though I lost a lifer, I gained a lot of knowledge about these two species and how to differentiate them. This knowledge will hopefully serve me well in the years to come, and is worth more than a tick on a checklist. Though it was kind of cool having a first Ottawa record while it lasted…! 🙂