7 – The Orange-Spotted Emerald, Oxygastra curtisii

 

Orange-Spotted Emerald, by RKJ, from Wikipedia

The Orange-Spotted Emerald ‘is the only species of dragonfly to have been originally described from Britain’ (Hawksworth, 2003).  The first specimen was found on ‘June 29th 1820’ (Brown, 1980) by James Charles Dale (whom you’ll remember from this series of articles as the man who didn’t discover the New Forest Cicada) on Parley Heath in what was historically Hampshire, but is now Dorset. I have been unable to determine if ‘Parley Heath’ is the same place as the modern ‘Parley Common’ – where the Smooth Snake was first discovered in the UK.

Despite being discovered in 1820, it ‘was not named and described by him [Dale] until 1834’ (Brown, 1980). According to Brown, the Orange-Spotted Emerald was then ‘lost sight of for a period of 45 years’ (Brown, 1980) until 1878 when H. Goss ‘took six examples on a heath to the north of Pokesdown, near Bournemouth’ (Brown, 1980) approximately two miles away from the original discovery site. I am left a little confused by Brown’s chronology here – specifically the 45 years of absence. Brown states that Dale first captured a specimen of Oxygastra curtisii in 1820, which he named 14 years later in 1834. Brown does not mention additional sightings or records of O. curtisii until those of Goss in 1878. Thus there appears to be a 58 year absence of sightings between 1820 and 1878 – so where has the figure of 45 years come from? Even if Brown meant 45 years from Dale’s description of the species (his description, I assume, being based on the 1820 specimen he presumably collected) in 1834, that only amounts to 44 years.  Odd.

Dale’s description of the Orange Spotted Emerald almost came too late – another entomologist, J. F. Stephens, independently discovered the species in 1829 and named it Cordulia compressa. However, as Stephens ‘failed to include any description with the name, the later Dale name survives’ (Chelmick, 2009).

 

Within the UK the Orange Spotted Emerald was only known to occur within Dorset and Devon. The Dorset records span from the discovery of the species in 1830 up to its presumed extinction from the UK in 1963 and all records were within the waterways of the Moors River and the River Stour. In Devon the species was recorded in 1946 only, on the River Tamar; a single specimen was obtained and two others were seen in flight. Despite searches, no Orange-Spotted Emeralds have been seen here subsequently.

As mentioned above, the species is presumably extinct in the UK since 19th July 1963, this being the date of the latest specimen taken.  Usually the reason given for its extinction is declining water quality/pollution, indeed, I hinted at such a situation in my previous article focusing on the Norfolk Damselfly, however, after reading the Chelmick’s review of the species from the Journal of the British Dragonfly Society – Volume 25 I am now less sure. It seems that whilst the extinction coincided with the enlargement of a local water treatment plant, there was no real decline in water quality due to this. Chelmick instead deduced that the extinction was due to habitat change, namely that trees had grown up alongside the water, reducing habitat for territorial males, and shading the river.  Supporting evidence is given by the fact that in 1990 the habitat had become so altered that ‘Platycnemis pennipes (White­legged damselfly), a species strongly associated with open lowland rivers and found commonly on the Moors River in the 1950s, was absent’ (Chelmick, 2009). This, then, seems a more plausible reason for the extinction of the species than that of water quality, though Chelmick also adds that 1963 was also the year of one of the harshest winters on record – could this possibly have had something to do with it?

 

The Orange-Spotted Emerald still occurs in Northern France, not obscenely far away from where it used to be found in the UK. However, the species has never been recorded as a vagrant (possibly not very dispersive? Or just overlooked?) and even if it did, for some reason, arrive in decent numbers, it seems as though there may not be enough suitable habitat for it to recolonise.

One nugget of positivity though, again from Chelmick:

‘It is not impossible that O. curtisii survives in Britain in hard to reach stretches of south-western rivers. I would propose that perseverance of observers with the cooperation of riparian landowners could be highly productive. Even if O. curtisii were not discovered, the increase in knowledge of our riparian fauna could only benefit.’ (Chelmick, 2009)

 

 

 

Brown, S.C.S. (1980) The Entomologist’s Record and Journal of Variation Vol. 92, T. Buncle & Co. Ltd., Arbroath, Angus.

Chelmick, D. (2009) Journal of the British Dragonfly Society – Volume 25, British Dragonfly Society.

Hawksworth, D.L. (2003) The Changing Wildlife of Great Britain And Ireland, Taylor & Francis Limited, London.

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