Saturday, 28 July 2018

Rare Emeralds

Regular readers may recall that a couple of years ago on the way back from the Western Purple Swampmonster I made a detour (see here) to see the Southern Migrant Hawkers at Wat Tyler CP and that I also tried for the nearby Scarce Emerald Damselflies at Bowers Marsh RSPB but came away without a definite sighting of the latter. Accordingly I've been meaning to go to try for the ScED again but never quite got around to it last year so this year I decided to make a bit more of an effort. Since my last attempt a resident breeding colony of ScED and also Southern Migrant Hawkers has become established at Canvey Island in Essex so I decided that this month I would pay a visit. With the weather forecast not being an issue in the prevailing heatwave I was just waiting for a convenient gap in my work schedule when I stumbled across some news on the British Dragonfly Society sightings page of a colony of Southern Emerald Damselflies in Buckinghamshire of all places! Now Southern Emerald is even rarer than Scarce and to my knowledge there were no public locations where this species could be found so I was keen for more information. The BDS report was rather vague on details so I started to do some investigation and eventually got all the gen. There seems to be some ambiguity as to whether this should be public information or not: I was told in confidence so I shan't give away any more details though it won't take much effort to find out all you need to know if you explore the BDS sightings pages in a bit more detail. Anyway, I elected to pay a visit to this location first and asked PL if he'd like to come along. He was keen so it was that we rendezvous'd just east of Oxford and in light traffic we'd soon arrived at the location. In the extreme heat we walked slowly down the footpath towards the general area where I'd been told they could be seen and it wasn't long before we'd found our first one in amongst some brambles. As we moved further down the path they became more frequent and near the hot-spot by the hidden pond we met a familiar face in the form of fellow Odonata enthusiast WB. With plenty of the SoED to be found, including lots in pairs, PL and I whiled away the time taking loads of photos.

Southern Emerald Damselfly is normally to be found, as the name suggests, in the southern countries of Europe though there is an established breeding population in the Netherlands now. As the climate in this country changes species such as this are increasingly going to colonise and this is surely just the first of many such finds. In terms of identification it can easily be picked out by the bi-coloured pterostigma (the dark wing patch towards the front tip of the wing) which is unique to this species for European Damselflies and which can easily be seen in the photos.

With theses bonus rare Emeralds in the bag, a few days later an opportunity arose to pay a visit to my original target, namely the Scarce Emerald Damselflies. My VLW was due to take her turn looking after her elderly mother in Surrey so I offered to drop her off on Sunday and then to nip around on the M25 to Canvey Island for my target. I say "nip" though in the end it was anything but that. With it being the first weekend of the school summer holidays, the traffic was very heavy and around by the Dartford Crossing it was crawling along and I spent some three quarters of an hour in a stop-start queue. Finally I was across and almost immediately was turning off towards south Essex where in much lighter traffic I made good progress and a little while later I was pulling up by the famous ditch which housed the first proper UK resident breeding population of Southern Migrant Hawker and also Scarce Emerald Damselfly. 

The normally water-filled ditch turned out to be almost completely dry though this didn't seem to matter to the SMH's and a patrolling male could be found every few metres along the ditch. The ScED on the other matter were much harder and it was a while before I found one skulking in the vegetation - I think that the rather overcast conditions meant that they weren't flying very much. As I worked my way along the ditch I managed to find quite a few more though I saw no where near the 50+ numbers that had been reported on-line. Still it was nice to see them and I whiled away the time trying to get some decent photos. I did manage to find a SMH actually perched and so get a proper non-flight photo and eventually also manage some reasonable ScED shots as well. 

Scarce Emerald Damselflies

This happless Hawker has been caught by a huge Wasp Spider

A couple of perched Southern Migrant Hawkers
Contrary to its name, Scarce Emerald Damselfly is actually one of the most widely spread species in the northern hemisphere, occurring in Europe, Asia and North America. However, it's never become well established in this country and various colonisation attempts in recent years have had mixed success. In terms of identification the males are distinguished from the similar Emerald Damselfly by the fact that the blue colour is missing from the low half of the S2 segment at the top of the abdomen. Other than that you have to get to grips with the differing shapes of the anal appendages. As far as breeding is concerned, like SoED, ScED lay eggs in vegetation which remains dormant over the winter before hatching in the spring so the fact that the ditch has completely dried up shouldn't matter to them at all. For the SMH on the other hand I think that their breeding cycle may well require the constant presence of water so it's possible that this colony might die out this year which would be a terrible shame.

1 comment:

World of Animals, Inc said...

It is incredible that you were able to capture the photo of the dragonfly caught in the spiderweb. Amazing wildlife photography. Thanks for the share, have a fantastic weekend. Keep up the posts.

World of Animals