|Male Parsonage Moor, Oxfordshire|
|Female, Dry Sandford Pit, Oxfordshire|
Coenagrion mercuriale, the southern damselfly, is a species of damselfly in the family Coenagrionidae. It is found in Algeria, Austria, Belgium, France, Germany, Italy, Liechtenstein, Luxembourg, Morocco, the Netherlands, Portugal, Slovakia, Slovenia, Spain, Switzerland, Tunisia, and the United Kingdom. Its natural habitats are rivers and freshwater springs. It is threatened by habitat loss.
The specific part of the scientific name, mercuriale, is because of the distinctive markings on the second segment of the abdomen that resembles the astrological symbol for the planet Mercury - ☿.  This also gives the species an alternative common name of mercury bluet.
They require areas of open vegetation, mixed with slow flowing water in which to lay their eggs.
The larvae spend 2 years underwater before emerging as damselflies.
Status in the United Kingdom
Places where they are found include the New Forest, Hampshire, Oxfordshire and the Preseli Hills, Pembrokeshire; where work is being carried out in 2015 to improve habitat. In 2009, 500 adults were captured and released in the Venn Ottery nature reserve in Devon. This nature reserve is owned and managed by the Devon Wildlife Trust and grazing has been re-introduced there to help encourage this species which had not been recorded there since 1988.
- Boudot, J.-P. 2005. Coenagrion mercuriale. 2006 IUCN Red List of Threatened Species. Downloaded on 9 August 2007.
- Costantino D’Antonio and Francesca Vegliante. "Derivatio nominis libellularum europæarum" (PDF) (in Italian). Retrieved 3 August 2010.
- "Checklist, English common names". DragonflyPix.com. Archived from the original on 4 December 2012. Retrieved 5 August 2010.
- "Conservationists restore habitat for endangered species". Western Telegraph. 12 April 2015. Retrieved 12 April 2015.
- "Southern damselflies released into Devon nature reserve". wildlifeextra.com. Retrieved 3 August 2010.
- "Wildlife and Countryside Act 1981". Government of the United Kingdom. Archived from the original on 30 August 2009. Retrieved 15 October 2010.