Quote:
Originally Posted by erdragonfly  As a recorder, my recommendation is never to identify a blue damselfy by one marking/feature alone. Two markings/features should be enough to pin it down to species. In my opinion there are three features above that are more associated with Variable than Azure. Segment two is clearly of no use for identification in this case. |
I agree with the above statement - and it doesn't only apply to blue damselflies. In all identifications all visible features should be taken into account, because relying on a single feature can easily lead to mistakes if that feature is atypical.
However, there are usually some features that can be given more 'weight' in reaching an identification than others:
Structural features are often far more reliable than colour markings, and in the case of blue damselflies (especially
coenagrion species), the shape of the rear edge of the pronotum is usually considered diagnostic.
On the three points highlighted by erdragonfly:
1). It is incorrect to say that the bar between the post occular spots is
never present in Azure Damselfly. It is
usually absent, which means that it is generally a very good pointer towards Variable, but on rare occasions Azure Damselflies do have this feature (usually it is indistinct, if present at all).
Male Azure Damselfly with obvious bar between post occular spots (but typical in
all other features;
Website of the European Dragonflies and Damselflies (Order: Odonata)
(Click on Zygoptera under European on the left hand side of the page, scroll down to find Coenagrion puella in the species list, click on male & then click where it says 'click here' to view the high resolution image - sorry but I can't seem to provide a direct link
).
2). IMO there is a thin pale edge to the rear of the pronotum on the individual in question, and this seems to trace a gentle, broad curve - which would be a very good fit for the central lobe of the pronotum of an Azure, but would not fit Variable (this is
not clear though so may be wishful thinking!
).
It is certainly not unusual for the rear edge of the pronotum of Azure to have the pale edge very thin or absent. Variable, on the other hand, rarely show a pale rear margin to the pronotum.
3). I presume that it is the black marking on segment 9 that you are referring to here (rather than 10, which is generally black on both species)? I agree that the square shape seems more typical for Variable, but this marking is highly variable on both species (a scan through images online, including the WAB
Gallery will confirm that).
One other feature that hasn't already been mentioned - the sixth abdomen segment is largely black, which is another feature than could suggest Variable (at least 1/2 the dorsal surface of this segment is usually blue in Azure). Some Azures do show more black on this segment though, so again it could fit either species.
My opinion is still on the side of Azure (largely because I
think that the pronotum looks good for that species. In the abscence of a clear shot of the pronotum, or any other truely diagnostic features, I would leave this one unidentified though.
A few images from the WAB
Gallery (all showing Azure Damselflies):
No obvious pale rear edge to pronotum + extensive (but not quite square) S9 marking:
Azure damselfly - Coenagrion puella - Wildlife Photography
No obvious pale rear edge to pronotum + extensive black on S6:
Azure Damselfly - Coenagrion puella - Wildlife Photography
No pale rear edge to pronotum:
Azure Damselfly - Coenagrion puella - Wildlife Photography
A very interesting individual anyway - I've enjoyed trying to confirm the ID!
Linear Mode
