Southern Damselflies

John Solomon, 10th July 2021

On 23 June a friend of mine, Brain Cartwright, a local birder who haunts Anton Lake, sent me a series of photographs he’d taken that day. There was no special reason for this, he’s keen on local wildlife and a very keen photographer, so he regularly emails the latest crop of images around other local naturalists. He also appreciates, or at least, I hope he does, my modest input for identifying Odonata. Largely, the photos were entirely predictable, a Tortoiseshell Butterfly, a Meadow Brown, several female Banded Demoiselles and so on. So far, so pretty, but then, the third photo from the end, slammed me between the eyes. Taken directly looking along the length of the back of the insect there was no mistaking the striking markings running down the top surface of the abdomen.

I was instantly back on the net and emailing him. Where had you taken it? When? No, exactly where. How far along the bank? I told him what it was … a male Southern Damselfly.

These are some of the rarest Damselflies in the country. They are on the wing through June and July. Their distribution is the Itchen, around Winchester, and the Test, up until recently believed to be limited to around Mottisfont. There is a notable residency in Pembrokeshire, and a small colony on Anglesey. Other than that it’s the very occasional few on Exmoor and a handful of tiny dots on the map. They’re covered by the GB Red List (Endangered), Protected in EU legislation, covered by the W&C Act of 1981, so it is illegal to catch or handle them without a licence, the NERC Act of 2006, which in this country covers only the Southern Damselfly and the Norfolk Hawker, and the UK BAP Priority Species listing. This last means that Biodiversity Action Plans have apparently been drawn up nationally to target them for actions such as monitoring, surveys and more practical conservation measures.

Two years ago the area recorder for North-West Hampshire, David Murdoch, found them at Bossington, just south of Houghton, and we went out one afternoon to try and find them further up the Test Valley. Ironically, the first site I took him to was Stockbridge Common. He decided it wasn’t really right for them, which leads us on to the environment they prefer. This is understood to be ditches and small chalk streams which are open, shallow and narrow, with shallow peat or silt over gravel and slow to moderate flows.

Brian told me that he had found this one on Stockbridge Common, on the reeds beside the branch of the River Test that runs down the almost mile-long western edge. That was both odd and exciting. That waterway was a river rather than a stream, and certainly nothing like a ditch. If they were there then that could expand the type of environment they might be found in, which also meant expand the territory.

The next day was rather poor weather, which seems to be the story of this summer, overcast and humid with a trace of a gusty wind, but nothing was going to stop me going off on a hunt! I parked in the car park, just off Marsh Court Road, and dragged all the gear out of the boot of the car – wellies, camera and monocular for identification. I locked the car and headed through the two kissing gates and onto the Common. I was not optimistic, in spite of Brian’s photo. These insects are not known for flying distances but Bossington was only a couple of miles downstream as the crow flies. Most likely a tourist, I thought.

A footpath from Stockbridge High Street emerges onto the Common over a narrow footbridge crossing a small stream. That was the first possible site I would come to and I reckoned it was the most likely place to find them, if they were here, rather than the larger river. It was barely 75 yards so very soon I was in hunter mode and creeping very slowly into the reeds … and within 30 seconds I’d found my first! The gusty wind made it impossible to get anything more then an identification photo, but there was plenty of time. I continued to search and managed to find another two.

It seemed that there was indeed a small colony here. I didn’t think they were really along the river itself, but I felt I deserved it to Brian to at least spend some time looking there for them. I left the stream behind and walked to the bank of the Test branch and started searching the reeds meticulously. Even though I suspected I wouldn’t find them here I most certainly wouldn’t if I didn’t look properly. After around 50 yards I found one and, eventually, another. Slim pickings, then I began searching patches of rough pastureland  a few yards away from the bank. This started working. After a couple of hours I’d covered around 150 yards and, with the three I’d found straight off, managed a count of 18. I returned to the car happy and with a new goal.

I’d established that they were here, now I needed to find out how far along Common the colony stretched. If it went the whole way down then this would not only be a new colony but a very significant one.

With a couple of other sites to survey for butterflies it wasn’t until 30 June that I managed to get back down to the Common. This time I actually pushed away from the river 30 or 40 yards and searched more the grasses of the Common itself, and this turned out to be a solid hunting ground. It could well be that the rather unappetising weather – gloomy, humid and still with that gusty wind – was driving them to roost. By the end of the afternoon I had counted 31 in total, being 24 males and 7 females, and had ascertained that the colony did indeed run the whole length of Stockbridge Common.

I have since been trying to find the insect further up the Test Valley and have visited Chilbolton Common three times and searched around Longparish, but to no avail. I’ve not given up yet! The weather has been poor and I think there are possible sites around Whitchurch, the problem being, as ever with a river that is known for its fishing, is getting access to the watercourse itself.

This is a male Southern Damselfly, fresh from Stockbridge Common, Latin name Coenagrion mercuriale:

The identification of the male is relatively easy. If you look at the insect from above, along the line of its back, you will see a series of black markings running up the centre that look rather like spearheads, which I have labelled “4”. At the top of the abdomen, near the thorax, on the second section of the abdomen, is a mark that closely resembles the sigil of Mercury – hence the  name “mercuriale”. This is labelled “3”. The circle labelled “2” shows you the Coenagrion Spur, which is the small black finger extending into the blue on the side of the thorax from the rear. This is also found on other species such as the Azure Damselfly and the Red-eyed Damselfly, but those species do not have the previously mentioned markings. The last and least important marking on the male is the fact that there is a bar of colour running between the eyes, which I have labelled “1”.

This is a male Azure and a brief comparison will make the two species very clear. There is no line of spear heads running up the top surface of the abdomen, the marking on section 2 is more like the outline of a bucket or beer glass than the Mercury sigil, and there is no colour bar between the eyes:

This is a female Southern Damselfly:

This is a blue-form female, they also come in a green form. She is almost identical to a female blue-form Azure, to the extent that many books will simply advise that because Southerns like moving water, unlike most, then wherever they are found they are often the only species of Damselfly. So if you find male Southerns any females you find are likely be female Southerns. This advice is not correct. The Azure is a species that can turn up in moving water, especially if there are areas of calmer flow, backwaters or reeds to offer shelter. The scientific method of telling the two apart involves examination of the pronotum, which is a tiny plate that runs across between the head and the thorax, the trailing edge of which varies between different species. Since you have to be licensed to catch the insect and do this that is an avenue unavailable to most of us. As it happens, it’s also unnecessary if you can get a half decent photograph.

The identifying markers on the female are exactly the same as for the male, except for the line of spearheads and the Mercury sigil. First, check for the Coenagrion Spur, as shown in the photo of the male Southern, above. If that is present and correct then examine the topmost side, or back, of the head. In the Azure the eyes almost touch and there is a blue or green splodge on them, depending on whether the insect is blue or green form. In the Southern there is a noticeable gap between the eyes and this gives room for a bar of the body colour, as on the male. I have marked these features on the photo below:

“1” is the bar of colour between the eyes and “2” shows the Coenagrion Spur. “3” shows the mark on section 2 of the abdomen which is usually so useful to identify species, but in this case is so similar the similar thistle marking on the female Azure that it is worthless as a defining characteristic.

The last photograph I am showing you is another male:

I am including this to show the variability of the markings in the insect.

In the more typical individual I showed earlier the spearheads running up the back of the insect are fairly chunky. I did, however, find this specimen in which those spearheads are rather minimal and more like sharp needles.

I finish with an earnest plea. These insects are very rare and at first I wasn’t sure that I should advertise their presence on Stockbridge Common. If you do decided to visit please respect their rarity, don’t catch them and if you come across any mating pairs please stay well away. We need as many of them as they can make!

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