Tuesday, 20 September 2016

Green Snaketail

On 10 September I went on a botany outing to the Ile du Passeur in the Loire River near its confluence with the Cher at Berthenay. Down on the island, which is currently accessible by foot because the water level is so low, one of the first things I saw was a largish dragonfly. 

I took a series of photos because it was clearly a clubtail Gompidae and I knew there was a rare species that only occurred on the Loire sands in France, although I had never seen it. Clubtails aren't all that easy to tell apart in the field, and it wasn't until I got home and checked the field guide that I knew that I did indeed have the rare species. It is always a bit odd when one just stumbles across rarities, they pose calmly for photos and turn out to be perfectly easy to identify once you know what you are looking for. 

In the case of the Green Snaketail Ophiogomphus cecilia, the most obvious diagnostic character is the short straight yellow appendages on the tip of the abdomen. My French field guide talks about the thorax being a very striking luminous green, almost fluorescent. Well, my specimen was old and faded, so although I thought it was an unusual mint green colour it would not have surprised me to find it was a faded clubtail of another species. The field guide also claims you could not mistake this species for anything else except a female Blue Hawker Aeshna cyanea. This is distinctly misleading. It would be very easy to mistake this dragonfly for several of the much more common clubtails that occur here. The key difference is that they all have dark spreading abdominal appendages or, in the case of the pincertails, much larger pincer shaped appendages.

The Green Snaketail (Fr. Gomphe serpentin) is a species with a rather patchy distribution. It needs flowing water on sandy gravelly substrates in the lowlands. It can be seen flying between July and early November. The one I saw was behaving typically for the species, spending minutes at a time resting on the ground. The species is protected in France, listed on the European Habitat Directive to ensure appropriate conservation actions are taken and used to be categorised as globally endangered on the Red List. Thanks to the control of development and pollution in many parts of its range in the last couple of decades things have improved though, and globally it is now categorised as not at risk. According to the French government agency the Office for Insects and their Environment (OPIE) more needs to be done to monitor the species population in France. The species is still considered endangered overall for France, but merely 'vulnerable' in Centre-Val de Loire. The factors affecting the species that OPIE are most concerned about are the increased use of riversides and an increase in the number of trees along river banks, both of which do not favour larval habitat.

I am very pleased to have seen this special species.

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