|Enallagma cyathigerum (Charpentier,
1840), the Common Blue Damselfly, is common in all of Europe, except for
Iceland. It is probably the most common of dragonflies and damselflies
throughout much of Britain. It is also common in most of Asia. The North
American populations have been found to belong to a separate species.
With a length of 32 to 35 mm, the
species is a small, brightly coloured damselfly. It is the bluest of the
blue damselflies. Males have a club-shaped black mark on second abdominal
segment and the upper surface of segments 8 and 9 is all blue. Males have
broad antehumeral stripes, the hind margin of the pronotum has a flat,
shallow median lobe. Females occur in three colour forms, typical, blue
and brown. They have a medial spine on the underside of segment 8.
In many ways this could be considered
to be the most typical British damselfly. It shares its blue and black
colouration with several other species. It can be distinguished from the
others by its broad ante-humeral stripes. In the male, S2 has a characteristic
mark of a spot linked to the inter segment suture by a short line. S8 and
S9 are entirely blue.
The female occurs in two colour
forms, one blue, as in the male, the other dull green. The mark on S2 is
thistle shaped and there is a "Christmas tree" shaped stepped triangle
They often perch gregariously on
emergent plant stems, all facing the same way.
It inhabits a wide range of habitats,
from small ponds to rivers. They are especially common at lakes and reservoirs.
During mating, the male clasps the female by her neck while she bends her
body around to his reproductive organs - this is called a mating wheel.
The pair flies together over the water and eggs are laid within a suitable
plant, just below the surface. The eggs hatch and the larvae, called nymphs,
live in the water and feed on small aquatic animals. Nymphs climb out of
the water up a suitable stem to moult into damselflies.
This species is easily confused with
the various members of the genus Coenagrion. Look at S2 (on the males)
for distinguishing characters. It does appear particularly blue compared
with other similar species. The females can be particularly tricky to distinguish
apart. The Common Blue Damselfly can be easily mistaken for the Azure Damselfly
(Coenagrion puella), but on the back and the thorax, the Common Blue Damselfly
has more blue than black; for the Azure Damselfly it is the other way around.
The second segment of the thorax has a distinctive spot with a line below
connecting to the third segment. Another difference can be observed when
inspecting the side of the thorax. The Common Blue Damselfly has only one
small black stripe there, while all other blue damselflies have two.
Enallagma cyathigerum is widespread
and common in large parts of Europe and northern Asia. In the northern
part of its range one of the most common damselflies. There is a possible
future threat from habitat destruction and water pollution, as some of
it's habitat is not as suitable as it could be, but that does not appear
to be having an effect on the global population yet. So it is classified
as Least Concern on the IUCN Red List 2006.