21 Jul 2014

21 July 14 - Caught Out By A Conman (Darter) Or The Pitfalls Of Darter Identification

If you're going to write a blog or publish stuff in another format, then there is always the risk that you will misidentify something. I've seen this on other blogs, where people have made errors & it's interesting looking at the different reactions. Some put their hands up & admit to the error, others probably change things very quietly hoping nobody spots they have made a mistake & on a few occasions, I've seen people carry on with the error regardless of the facts. Another reaction I've seen from a well known figure & prolific tweeter has been to suddenly go quiet for a few hours after being told he has made a mistake. I'm looking forward to his next mistake to see if this was pure coincidence or another interesting approach. My approach is to put my hand up to the error & try to learn from the mistake, so I don't make it again. 

Over the weekend, I was finally looking at some old photos from a couple of years ago & labelling them. I found this Darter photo from Dorset's newest birding site, Longham Lakes. This has been well watched over the last four years since the gravel extraction phase at this site ended. I didn't look at this photo really closely, but labelled it as a Red-veined Darter.
Darter: Longham Lakes (18 Aug 12)
This went out as an email on the local email group as I don't remember any records of Red-veined Darters for this site. It prompted a swift & private response from my sharp eyed mate, Steve Morrison, asking whether I had attached the right photo as this was a Common Darter. A quick look in this case, revealed he was right, as I couldn't even see any red veins on it. I had been going on the red pterostigma (the red cell at the end of each wing) & hadn't really checked the photo more carefully. Oh dear. Should have looked at the photo and the books a bit more closely. At this point, I forwarded a photo of the Red-veined Darter taken at Arne recently to ensure that I hadn't screwed that one up as well. That one had red veins, but having re-read the Dragonfly guide, the pterostigma should be yellow-brown with a dark line above & below and alarm bells starting ringing about this one. But on balance, I still thought this would be OK. 
Darter: Arne (11 July 14)
The email back from Steve confirmed that this too was a Common Darter. I quickly contacted Brett Spencer as Brett probably knows more about Dragonflies than anybody else I know who now lives in Dorset. Steve lives in France these days so I don't have to try comparing their knowledge (phew hopefully that will avoid a legal action!!!). A quick response from Brett confirmed the Arne Darter was a young male Common Darter. So that's now two misidentifications & the Arne Darter was already published on the blog. I only had time last night to quickly add a brief update to that post, but have now changed it. But rather than adopt the approach of constantly rewriting history like the Ministry of Truth in George Orwell's classic book 1984, I thought I would try to get the features sorted properly this time. I've often tried to make the blog a bit more interesting than a diary of what I saw when I went out. So I've tried to add a bit more to the blog, e.g. subspecies & ranges or the features which make this species what it is. My worry now was have I mislead anybody else due to my errors.
Common Darter: Arne (11 July 14). Common Darters have 2 obvious yellow stripes on the sides of the thorax
 Common Darter: Arne (11 July 14) They also have yellow stripes on the black legs (would be all black in Ruddy Darters). The facial pattern has the black above the frons [nose area] extending as a line, but not going down the sides of the frons (which it would do in Red-veined Darters). The eyes are reddish-brown with yellow or green below & get redder with age, but never getting as deep red as on a Ruddy Darter
Common Darter: Arne (11 July 14). Males have an orangey-red abdomen. Clearly, from my photos the pterostigma colour can vary from greyish in the first individual to red with a touch of yellow in this individual. Note, the lack of yellow bases to the hind wings
Here are the comments from Steve on the above individual: The Arne photo gives the impression of something good based on the colouration of the veins, but not enough to be Red-veined and they really are red or orange-red in Red-veined. Common Darters have the most parallel sides of the Sympetrums. There is variation in Common Darters, as with many Dragonflies and some do show coloured veins. The Arne one being closer to the extreme than most. The pterostigma on Common invariably appear reddish and usually dark, but sometimes pale, but invariably reddish. Brett added that a Red-veined Darter would only ever have this extent of red on the pterostigma on an old male.

I did send Steve my final photo of a Red-veined Darter from West Bexington last year. I was confident about this one as the local birders, Mike Morse & Alan Barratt, took Peter Moore & myself to this site & others including Brett had also seen them earlier in their flying period. But there was always the possibility I had photographed a wrong individual, but this time I thought I was right. This got a thumbs up from Steve, so it can stay on my Life & Dorset list.
Red-veined Darter: Note, the brick-red abdomen, yellow-brown pterostigma with dark borders & yellow basal patches to the hind wings (although Common Darters can show this, but not as extensively). The red veins are mainly on the basal part of the leading edge of each wing. Unfortunately, I've not got a picture of the facial pattern to see the black ending down the sides of the frons. Other features to look for are the brown thorax lacking pale stripes, the eyes of males are reddish-brown above and blue below (but all are hidden on the photo by the wings) & the black legs have a yellow stripe on them
Steve has added the following comments against this individual. The veins in this individual are actually relatively indistinct for a Red-veined Darter and close to the Arne Common Darter, but they are always more extensive than Common Darters. Also note the more subtly pinched-in look at the Red-veined Darter abdomen (not applicable in females). Also the pair of red tips on the ante-alar ridge [part of the edge of the thorax in front of the front wing bases], just in front of the red tegulae [the bit where the wing joins the thorax] are more diagnostic of Red-veined Darter, than Common Darter. On a Common Darter, this area usually looks pale contrasting with the red tegulae, as seen on the Arne Common Darter. Wow got a couple of new bits of anatomy into the post, which I had to look up on the internet. I've added my layman's explanation in square brackets.

Overall, it has been a good learning experience for me. Many thanks to Steve & Brett for their comments on the Arne individual. Also thanks to Steve for having a proof read of this post to make sure it was OK before publishing it. Can't wait to get back out now to have another closer at Common Darters and hope that some more Red-veined Darters appear in Dorset this year, to get a better view & photos of them.