Length: 29-31mm

Flight period: June to August (occasionally May)

C. mercuriale mercury markThe Southern Damselfly, Coenagrion mercuriale, is one of several members of the genus Coenagrion currently to be found in the British Isles and is a member of the family Coenagrionidae.

Male: distinctive ‘mercury’ mark on segment 2 of the abdomen (see right – Copyright Environment Agency, 1999). Also use the coenagrion spur on the side of the thorax and a small blue line between the eye spots as additional, but not distinctive, features.

FemaleCoenagrion species are very similar making them difficult to identify.

The flight is weak and low; they stay close to the breeding site and do not appear to disperse easily to colonise new areas. Low shrubs and Juncus spp. are used for perching, roosting and feeding forays.

Eggs are laid in submerged tissues of aquatic and emergent vegetation and the plant dwelling larvae usually take two years to mature.


The larvae are distinctive in that they have very small, unpatterned caudal lamellae.


Southern Damselfly Management Handbook


Where to See

Latin NameCoenagrion mercuriale

In the UK the Southern Damselfly is primarily a species of base-rich runnels and streams often within acid heathland areas. However, it also occurs on water meadows in the flood plains of two chalk rivers, a habitat said to be more typical of many continental sites. At breeding sites the water is typically shallow and slow-flowing over a gravel or marl bed with patches of organic detritus. It may be that a more or less constant, relatively high, water temperature in winter in the spring-fed sites is particularly important in determining site suitability.

Status & Distribution

The Southern Damselfly is a rare species in the UK. In the UK, it is living on the extreme north-western fringe of its European range. Its two main strongholds are in the New Forest, Hampshire and the Preseli mountains, Pembrokeshire. Smaller colonies are found in Devon, Dorset, Anglesey, Gower, Oxfordshire and on the flood plains of the Test and Itchen rivers in Hampshire. There are old records from Cornwall and Somerset and elsewhere in Devon, Dorset and South Wales. The range of the species has contracted in the last thirty years.

The main factor thought to be influencing the decline of the species is the removal of grazing animals that maintain the open nature of the species’ breeding sites. Other potential threats are abstraction of water, leading to a lowering of the water table, drainage due to agricultural and forestry pressures, and excessive nutrient enrichment from the runoff of nitrogenous fertilisers from adjacent agricultural land. Isolation and scarcity of habitats is a cause for concern.

Beyond the UK, the Southern Damselfly’s distribution is in Western Europe, principally around the western Mediterranean, including Northwest Africa. It has vanished or is on the edge of extinction in 7 countries situated along the northern boundaries of its distribution (Belgium, The Netherlands, Luxembourg, Slovenia, Romania, Poland, Austria) and is declining in 3 others (UK, Germany, Switzerland). A world distribution map of Southern Damselfly can be found in Askew, R. R. (1998), The Dragonflies of Europe, Harley Books.

A very useful account of the ecology of the Southern Damselfly is available to download as a .pdf document.

This species is protected under Schedule 5 of the 1981 Wildlife and Countryside Act, as amended, which protects it against a variety of factors including killing or selling of individuals and damage or destruction of habitat. In Great Britain this species is classified as Rare (category 3) on the Red Data Book List (it also features on the red list of other Countries in Europe), and it is a British Dragonfly Society “Key Species”.

It is also listed in Appendix II of the Berne Convention and Annex II of the EC Habitats Directive, which is transposed into UK law through the Conservation (Natural Habitats etc.) Regulations (1994), commonly referred to as the Habitats Regulations. Under the Regulations sites of significant ecological importance within a European context for their habitats and/or species populations have been proposed as Special Areas of Conservation (SAC). In the UK there are more than 10 candidate SACs with one of the qualifying criteria being the presence of Southern Damselfly.

The UK Biodiversity Steering Group published the UK Biodiversity Action Plan (BAP) in 1995. This identified the Southern Damselfly as a priority species for conservation action and included (Volume 2, page 132) a Species Action Plan (SAP) for the species. More information is available here. The UK BAP accords with and implements the UN Convention on Biological Diversity, signed at the Rio Earth Summit in 1992. Its overall goal is to conserve and enhance biological diversity within the UK and to contribute to the conservation of global biodiversity.

To co-ordinate implementation of the UK Southern Damselfly SAP a Steering Group was established in 1997. This partnership of organisations comprises: Environment Agency (Contact Point), The Wildlife Trusts (Lead Partner), Natural England – formerly English Nature, Countryside Council for Wales and British Dragonfly Society. Subsequently academics from Liverpool University were co-opted onto the Group.

The published objectives of the Southern Damselfly UK SAP can be found on the UKBAP site.

Many efforts to conserve the Southern Damselfly pre-date the publication of the Species Action Plan (SAP), and much of that work has been initiated and carried out by BDS members, often at their own expense and time. The purpose of the SAP is to provide a framework through which to provide co-ordinated direction to this on-going and future work and to attract and focus resources to achieving the range of actions identified in the Plan.

The species has undoubtedly benefited from the positive habitat management, surveys and monitoring by bodies such as RSPB and National Trust, and in recent years the SAP has inspired others such as the Forestry Commission, Dartmoor National Park Authority and many others to carryout their own works on Southern Damselfly sites. For example, the MoD and English China Clay have worked in close partnership with EA, EN and RSPB to manage and monitor the Bovington Ranges in Dorset. In that respect the SAP is already becoming a great success, the renewed habitat management efforts and new resources building upon the long-standing surveys and monitoring done by BDS volunteers.

Similar Species

This species is easily confused with the other members of the genus Coenagrion and with the Common Blue Damselfly Enallagma cyathigerum . Look at S2 (on the males) for distinguishing characters. Southern Damselfly is quite small compared with other similar species and will only be found flying in full sunshine in the hottest part of the day. The females can be particularly tricky to distinguish apart.

Species GroupDamselflies
Identification Notes
  • Male Blue with black markings including distinctive ‘Mercury’ shape on second segment of abdomen.
  • Female predominantly black with narrow green patterns on abdomen.
  • Rare species found on small streams and flushes in Southern England with smaller colonies in Devon, South and North Wales.
  • Length: 29mm.
  • May – August