Friday, 8 July 2011

The Great Emerald Mystery - Solved at Last

Finally got to grips with Emerald Damselfly today, about a fortnight after seeing my first at Far Pasture. Gibside Lily Pond came up trumps in a fleeting visit while picking up the weekly farm shop order. Not a particularly nice day as it happens, overcast but warm, not much wind and the threat of showers at anytime. Plenty of damsels about, many blues, mostly common, in contrast to my visit at the end of May when the blues consisted entirely of Azures. This seems to be a trend so maybe I can deduce from this that though both species inhabit the same ponds the Azures emerge earlier than the Common Blues. Best photo I got was this Azure mating wheel:



Azure Damsels - mating wheel
The first Emeralds I encountered were a tandem pair, great for comparing the sexes, a bit distant for a really sharp photo but the one I got shows the contrasting colouring of male and female, and the typical spread-winged perching stance which as reported earlier is a generalisation rather than the rule.

Emerald Damselfly - tandem pair
male top female bottom
 Individuals of both sexes later showed well and close enough to get good shots of them, clearly identifiable with the male blue tail segment a dead giveaway.

Emerald Damselfly - male
note tell-tale pale blue tail segment, overall green and blue
colouring and spread-winged pose
Emerald Damselfly - immature male
tinged with red and looking more like a skinny female,
this male will develop it's blue pruinosity with age.
Any confusion species? Well not really once you get your eye in, their flight action is fairly weak compared to other damsels, and obviously the spread-winged perch is diagnostic, but on individuals perched with wings closed, I have been fooled when I was less experienced by a very dark over-mature male specimen which I took for a blue-tailed, but a closer look sorted that one out quickly, and on mature individuals the blue/green colouring sets it apart from any other damsel in the region. The female I suppose bears a passing resemblance to the female Banded Demoiselle, but the demoiselle is a much larger insect, with much larger wings and is metallic green all over, see the comparison below to see what I mean.

Comparison of females - Emerald (top) Banded demoiselle (below)
At first glance very similar but compare the length of the wings.
The tail is clearly visible on the Emerald but the wings cover the entire
abdomen on the demoiselle, and once you have seen both in the field
the overall size difference of the insects is clear. Simple as that. 
And finally we haven’t really covered the Banded Demoiselle in any great detail yet as I was unsuccessful on my last quest for them, so meantime here is an excellent photo of the male by Steven Fryer (the female above is also courtesy of Steve).
Banded Demoiselle male - What a beauty!
But note the wings don't cover the whole body unlike the female.
S. Fryer

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