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Those Darn Darners
On an earlier page I posted a photo of Blue-eyed Darner  Rhionaeschna multicolor, taken at the Odello Lagoon, Carmel River mouth, Monterey County; reposted below at somewhat larger size. Today I was reading Tim Manolis's book (2003) and Kathy Biggs' useful web site, trying to figure out how one would identify California Darner Rhionaeschna california which, according the map of Kathy's site and the checklist on the U.Texas site, had never been recorded in Monterey County (MTY, to use the standard bird observation abbreviation for the county). This is despite the fact that Manolis (2003) shows it within range here, and despite the fact it had been recorded in almost all the neighboring counties.
Using Manolis (2003), I had initially identified the above dragon as R. multicolor because of the blue eyes and blue face without an apparent dark cross-bar across the face between the frons and the clypeus. Today I further noted that in addition to the two blue side stripes on the thorax, it also had a pair of short blue stripes atop the thorax, and noted that the whitish spots of the final abdominal segment were widely separated. These are all consistent with Blue-eyed Darner R. multicolor.

As luck would have it, I had actually photographed two darners at the Carmel River mouth that same day (7 July 2006) and assumed they were the same species. They were about 500m apart; the Blue-eyed Darner (above) was very close to the lagoon while the other one (below) was in drier habitat along the trail to the lagoon. In looking at the photo of the second darner (below) I noticed that (a) the eyes were not as all-blue; (b) the pale blue face had a hint of a cross-bar; (c) the front and top of the thorax was all-brown without the short bluish stripes shown on multicolor; and (d) the two pale spots on the terminal segment were close together instead of widely separated. I began to wonder if this was California Darner  R. californica.

More importantly, the Canon 10D digital image picked up the terminal appendages as well. The two species can be separated by the shape of the cerci (the paired upper appendages) in both sexes: R. multicolor (below left) has a forked cerci shaped rather wrench-like, to use Kathy Biggs' words while the cerci of R. californica (below right) is not forked but paddle-shaped. Note that this shot also shows the difference in the placement of the pale terminal spots.
So it turns out that I had, quite by accident and/or luck, photographed both species of Rhionaeschna darners at the Carmel R. mouth, MTY, on 7 July 2006. Here they are side-by-side: Blue-eyed Darner R. multicolor (left) and California Darner  R. californica (right). Tim Manolis has graciously confirmed these identification, and further notes that while I did not notice any apparent difference in size between the two (California averages smaller but can approach Blue-eyed in size), the photos do show the more robust thoracic shape of multicolor.
Although this may be the first MTY record of California Darner to come to the attention of those currently keeping county checklists, I suspect that it is widespread and possibly common in Monterey County. It just happens that MTY may not have been surveyed much for odonates before; it may also be the case that prior records of R. californica here were overlooked in previous literature searches.
Literature cited:
Manolis, T. 2003. Dragonflies and Damselflies of California. Calif. Natural Hist. Guide 72. Univ. of Calif., Berkeley, CA.

PHOTOS: All photos are © 2006 Don Roberson; all rights reserved.






Page created 19 July 2006