1044 Southern damselfly Coenagrion mercuriale
Description and ecological characteristics
The southern damselfly Coenagrion mercuriale has very specialised habitat requirements, being confined to shallow, well-vegetated, base-rich runnels and flushes in open areas or small side-channels of chalk rivers. Most sites are on wet heath.
The larvae live in flushes and shallow runnels, often less than 10 cm deep, with slow-flowing water. Adults fly from June to August. Females lay eggs onto submerged plants, and the predatory aquatic larvae probably take two years to mature.
European status and distribution
Coenagrion mercuriale is widespread but rare in southern central and south-west Europe, and its range extends to northern Africa. The fairly stable centre of distribution in the south-west of the UK appears to constitute a major European stronghold of the species.
UK status and distribution
In the UK Coenagrion mercuriale occurs mainly in south-west England and in south Wales. It has declined in many places and appears to be present only in low numbers at most of its localities. However, more recently the decline may have ceased, with some evidence of recovery in numbers. Strong populations, numbering hundreds to thousands, occur in Dorset, the New Forest and the Itchen Valley in Hampshire, and on the Pembrokeshire Commons.
Site selection rationale
Sites for Coenagrion mercuriale have been selected to include the largest known populations in the main part of the species’ range in south Wales and south-west England, where the prospects for long-term conservation of habitat structure and function are good. Smaller populations occur elsewhere, and the larger of these sites have been selected to provide fuller geographical coverage. Most of the selected sites support Coenagrion populations on wet heaths, and are also selected as SACs for 4010 Northern Atlantic wet heaths with Erica tetralix. Populations associated with chalk rivers are also included within the site series.
A valley mire at 280 m altitude supports a southern damselfly Coenagrion mercuriale population of 20–100 individuals, first discovered on the site in 1998. The stronger population occurs in the northern portion of the mire, where springs feed shallow soakways that flow through wet heath. The southern part of the mire has a higher water table with Sphagnum bog-mosses dominating.
Dorset and Somerset
This site in south-west England, along with Dorset Heaths (Purbeck and Wareham) and Studland Dunes, represents the Dorset stronghold of southern damselfly Coenagrion mercuriale. The large size of the two cSACs, and a long history of records indicating well-established populations, should ensure the future viability of the small populations that occur here.
Dorset Heaths (Purbeck and Wareham) and Studland Dunes
Dorset and Somerset
This site in south-west England, along with Dorset Heaths, represents the Dorset stronghold of southern damselfly Coenagrion mercuriale. The large size of the two cSACs, and a long history of records indicating well-established populations, should ensure the future viability of the small populations that occur here.
East Devon Pebblebed Heaths
This site holds two relatively small populations representing southern damselfly Coenagrion mercuriale in the south-west of its range in England. These populations occur in wet flushes within the site.
Gower Commons/ Tiroedd Comin Gŵyr
Gower Commons, supporting small populations at two localities, represents southern damselfly Coenagrion mercuriale in south Wales.
West Wales and The Valleys
Representing southern damselfly Coenagrion mercuriale in west Wales, Preseli is one of the strongest populations in the UK, with numbers of adults estimated to be in the thousands and with a long history of records. Conditions on the site, created by its current management, appear to be optimal for this species.
Hampshire and Isle of Wight
Strong populations of southern damselfly Coenagrion mercuriale occur here, estimated to be in the hundreds of individuals. The site in central southern England represents one of the major population centres in the UK. It also represents a population in a managed chalk-river flood plain, an unusual habitat for this species in the UK, rather than on heathland.
The New Forest
Gloucestershire, Wiltshire and Bristol/Bath area, Hampshire and Isle of Wight
The New Forest in central southern England is an outstanding locality for southern damselfly Coenagrion mercuriale, with several population centres and strong populations estimated to be in the hundreds or thousands of individuals and with a long history of records. With Preseli, Dorset Heaths and the River Itchen, it represents one of the four major population centres in the UK.
SACs where this Annex II species is a qualifying feature, but not a primary reason for site selection
Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access.
Please note that the map shows sites where the presence of a feature is classed as ‘grade d’, but these sites are not listed. This is because ‘grade d’ indicates a non-significant presence.