Southern Damselfly Coenagrion mercuriale female

[JRsbugs]

What a surprise! I feel certain this is correct, it just doesn't fit any of the normal ones I have had. I had more shots but they weren't as well focused so I deleted them in camera, however I'm sure this shows all that needs to be seen.

Taken on 11th May in my garden, hoepfully it will be breeding in the pond!

If anyone is going to say it isn't this please tell me why, it looks to have all the correct marks.

Janet

[GuyF]

Hi Janet,

In my opinion this is a female Azure.
Female Coenagrion damsels are extremely similar, and the differences between them are subtle, but my reasoning for this is:
1. There is no pale bar between the eyes - there probably is variation in this, but it would still be very unusual for a Southern Damselfly to show this whereas it is a key feature of Azures.
2. The pronotum shape - this is very similar between the two species, but in Azures the hind edge is slightly more wavy, and from what I can see on your individual it looks closer to the Azure shape.
3. Structure - probably subjective, but female Southerns do have a distinct stocky, compact shape whereas this has the typical slender Azure shape.
4. Pterostigma shape - I've no idea whether this is a useful feature and I expect it may vary (hopefully someone else can comment!) but the photo of a female Southern that I have has a relatively short, rounded pterostigma, compared to the Azures longer, pointed pterostigma (as shown by your damsel).
5. Distribution! - I know that insects can show up virtually anywhere, but a Southern Damselfly in Lincolnshire really would be extraordinary! These are generally weak flyers, and highly sedentary and it would be unusual for one to show up so far from any colony.

Guy

[RoyW]

I'd agree with Guy on this one. The photo isn't from the best angle from which to view the shape of the pronotum, but I wouldn't exclude a female Azure based on what is visible. The lack of a bar between the post ocular spots is a more visible feature, which does strongly point towards Azure - I have seen Azures with the bar but most lack it, and although they may(?) occur I have not seen a Southern without the bar.

The shape of the pterostigma is sometimes given as an identification feature, but it is difficult to use because it can be variable. The pterostigma on southern tends to be a shorter diamond shape (with somewhat rounded corners), compared to the more stretched parallelogram of Azures, and is also sometimes noticeably darker in the centre (more of a solid colour in Azure).

[JRsbugs]

Thanks Guy and Roy, wow these are so similar! One I had last year in copulation was the more obvious colour form, but I have a pic of a female from 2008 which looks like this and at the time I had thought it was an Azure.

I have been sending myself silly trying to find out more about these!

If you look on Delta-intkey the bar on the head isn't mentioned. The pterostigma are described for the two species exactly the same. If anything, the Azure I had last year has a more rounded looking pterostigma.

British Insects: Odonata - Coenagrion mercuriale (Charpentier, 1840)

British Insects: Odonata - Coenagrion puella (Linnaeus, 1758)

The description for the female C. mercuriale does match well, there is no mention of the same patterning like this for C. puella other than In addition, there are blue forms of the female that are more or less intermediate in pattern between the typical male and the typical female forms); without mid-dorsal spots. In both cases, the abdomen is said to be "very slender"

The one thing which is hitting me in the eye is for C. mercuriale: The front of the head immediately interior to the eyes pale whitish blue.

For C. puella it states: The front of the head immediately interior to the eyes not pale whitish blue (mostly black).

If I have that correct, the part on the face between the eyes is blue in C. mercuria? I can only see a blue strip above the clypeus.

One other thing which is confusing me, for both species it states: The wings exhibiting 3 psqs cells between the quadrilateral cell and the subnodus

I'm not sure where that is, but if it's the cells anterior to the part which is divided somewhere just below the pterostigma, then mine has 4 cells on the forewing.

Finally, the distribution for C. mercuriale on Delta-intkey states: "Southwest Wales, southwest England, and central southern England".

Distribution maps cannot ever be taken for granted as I have shown I have species of insects which are said to be only in a very southerly and sometimes only coastal location. If you take a look at this thread you will see I have even some which are not yet recorded.

[JRsbugs]

What do you make of this? I found a digital scan of Coenagrion puella wing venation. The objective was to map the slightly varying locations of certain points according to different areas they were found in.

http://pcwww.liv.ac.uk/~chassall/Has...%20-%20IJO.pdf

I don't know if this is a fore or hind wing, but whichever it is there is a different number of veins between node 5 and the pterostigma. I count 12 on that, mine has 10 on the forewing and 11 on the hind wing.

Besides that, there's 6 cells in mine as opposed to 5 cells in the second row under the pterostigma to the wing tip, marked in my pic as 'A'.

As the forewing has 4 cells where I have marked 'A1' and the hindwing has 3 cells, the digital wing must be a forewing. There's an extra vein in the cell as marked on the wing tip on mine too.

[JRsbugs]

I've spent more hours trying to work this out!

First, I think the wing on the pdf is of a male. I checked the veins from the costal node to the pterostigma on the male of the mating pair of Azures I had last year, it definitely has 12 veins on one wing I can see well. I can only see the wing of the female in one pic, the others have wings together. It looks to have 13 veins.

Checking other pics I can find most look to have more veins which are closer together, one or two distant shots looked to have 10 on a female but they could be incorrectly identified.

Surely the wing venation is an indication of species and does not vary in the number of veins as in other insects?

Look on this site, a pic of a female C. mercuriale on the bottom row looks to have 10 veins on one and maybe 11 on the other wing, they are quite easily seen.

[wint]

Hi Janet

Thanks for those links to delta-key. Unfortunately they don't seem to mention the one diagnsotic feaure which is used to separate the female Coenagrions - the shape/pattern of the pronotum.

Like Guy and Roy, to me the rear edge of the pronotum in your excellent image looks to be wavy like Azure - I would expect a female Southern to show a very shallow straightlined V (with a notch in the middle). As also mentioned by Guy and Roy I would expect to see a pale bar between the eyes in a female Southern. In the images I have managed to obtain (and it's a rare damselfly even here in the south Hampshire area) each female has the pale bar between the eyes.

This website is one I recommend for detailed descriptions by images.

The Southern Damselfly is a poor disperser and there's an excellent paper from the University of Liverpool. There are areas in the New Forest with suitable habitat only a mile over a ridge from a Southern Damselfly site and yet Southerns have never been recorded.

There is intra-species variation in venation in Dragonflies (although I would need to by a DSLR and sharp Macro lens to see them )

Hope that is of some help.

[GuyF]

Out of interest, after spending a bit of time looking through images of Southern Damselfly I've yet to see one that is lacking the pale bar between the eyes, and I've never seen one in the field lacking this feature either. On the other hand, almost all Azures lack this pale bar. So while it may not be 100% reliable, it would certainly make your damselfly an 'odd' Southern if that's what it was, but personally I can't see anything which should rule out Azure on this individual.
Here's a shot of a female Southern from a Dorset colony showing the pale bar between the eyes (and, I think, a subtly different structure).

If you happened to have any shots that showed the pronotum clearly (or if you can find her again today!) that would be conclusive, because as wint says this is probably the single most important feature.
Guy

[JRsbugs]

Thanks for the French link wint, although there is nothing there which mentions the shape of the hind edge of the pronotum nor the bar on the head that I saw at least, it was more genreal for the genus.

Slight variations in wing venation is one thing, but so much variation is in my thinking surely dubious?

The pdf on Coenagrion puella wing venation which I linked to was merely to show the varying locations of certain nodes and cross points, illustrating the very slight different locations of these points which were possibly attributable to the differing sizes in wings. There was no mention of a cellular or venation variation that I could see, I read most of it. It would have made a mockery of the exercise if there had been such variations!

It appears (to me at least) that there has been at some time in history someone who has detailed these extra ID pointers, which may or may not be accurate or consistent. There are other variations which seem to be acceptable as 'variations' but these two features are deemed to be fixed and unvariable.

I am looking at this with a fresh mind, not one which has followed the rituals of identification. I don't wish to offend anyone, and I do respect the knowledge which has been gained by those who have been looking at these for donkeys years but I am the type of person who will not follow unless I have absolute proof. I hope you will understand this too, science sometimes gets stuck in a stereotypical rut.

I'm going to keep looking at these, and check out any good views of wing venation I can find as I find it very difficult to believe there can be such a big variation within one species. I will crop off the female wings which I have from last year to show how different they are, it wasn't the best view of wings but sufficient to see the big differences.

If anyone has proof of such variations in wing venation I would be pleased to see it. If the wing venation had matched the Azure I would be more than happy to say yes, that is correct.

[tristanba]

Just a brief comment on wing venation in leafhoppers, which I have noticed can vary within species. Certain fixed wing venation characteristics are useful identification characters because they always differ between species but there are few of these and most characters are variable. I can't comment on the situation with respect to Odonates, but would tentatively suggest it might be similar?