|Coenagrion is a genus of damselfly
in family Coenagrionidae, commonly called the Eurasian Bluets (although
three species are found in North America, C. angulatum, C. interrogatum,
and C. resolutum)
Coenagrion mercuriale (Charpentier,
1840), the Southern Damselfly (Coenagrion mercuriale), is a species found
in Western Europe and Northwest Africa, and is mainly centred on the western
Mediterranean. In Great Britain it reaches the north-western extreme of
its range. 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. Subpopulations in Italy
are sometimes regarded as a distinct subspecies, Coenagrion mercuriale
castellanii, but the so-called differences between the two taxa are not
The species has a body length 23-26
mm. Males are sky-blue and black in colour, with blue eyes and two small
eyespots. They can be distinguished from the males of similar species by
the blue 'mercury mark' on the second segment of the abdomen, but detailed
examination of the anal appendages is the only reliable method. Females
do not possess these anal 'accessory genitalia' but have an ovipositor,
which is not always easily visible. Females are generally green or blue
and slightly lighter than males in colour, becoming brown as they age.
They tend to have similar markings to males on the head and thorax but
have darker abdomens. In both sexes the wings are clear with small black
marks towards the tips.
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.
The southern damselfly breeds mainly
in heathland streams as well as chalk streams and calcareous mires. They
require areas of open vegetation, mixed with slow flowing water in which
to lay their eggs. Adults can be seen flying between mid-May to August,
the flight is weak, and they tend to stay level with grasses and other
vegetation. As with all odonata, males and females fly linked together
in tandem whilst mating, forming the 'wheel position'. When female southern
damselflies lay their eggs, they often remain in tandem with the male and
drag him below water where the eggs are laid on submerged or emergent vegetation.
The larvae, which are voracious predators, hatch soon after the eggs are
laid, but development to the adult stage takes 2 years.
This species is mainly an Atlanto-Mediterranean
species, found in Algeria, Austria, Belgium, France, Germany, Italy, Liechtenstein,
Luxembourg, Morocco, the Netherlands, Portugal, Slovakia, Slovenia, Spain,
Switzerland, Tunisia, and the United Kingdom. It is thought that 25% of
the worlds population exists within the United Kingdom but it has declined
by 30% since 1960 due to changes in grazing, land drainage and water abstraction.
This species decreases in density and frequency in other climatic areas.
The species is one of Europe's most threatened odonate species. It is on
the edge of extinction in seven countries and is declining in three others
including the UK. C. mercuriale is the only British resident odonate to
be listed in the European Habitats Directive that requires member states
to designate special areas of conservation for its protection.
Coenagrion mercuriale is classified
as Near Threatened (NT) on the IUCN Red List 2006, and Rare under the GB
Red Data Book. Listed under Appendix II of the EC Habitats Directive and
Annex II of the Berne Convention, and is protected (in 1998) under the
Wildlife and Countryside Act of 1981 of UK and features in the UK's Biodiversity