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Somatochlora metallica (Vander Linden) Brilliant emerald
Description S. metallica is slightly larger than the other two resident corduliid species, and
has a greener appearance. It is readily distinguished from S. arctica and
Cordulia aenea, which it resembles, by the distinctive pattern of yellow facial
markings and the shape of the anal appendages. Also, in females, there is a
very prominent spike-like vulvar scale which projects almost perpendicularly
to the body on the ventral abdominal surface between segments 8 and 9, and
is almost as long as those two segments. The eyes are green. The thorax is
bright bronze-green and not so heavily downy as C. aenea. The abdomen,
which is slightly club-shaped in males, is dark metallic green with a bronze
sheen. There are pale yellow markings on abdominal segments 2 and 3, both
laterally and ventrally and, in females, two small spots on segment 3 dorsally.
There is a small amber area at the base of the wings which, in mature females,
are entirely suffused with a pale amber tint.
Habitat In south-east England, S. metallica breeds on mesotrophic, neutral to mildly
acidic, ponds, lakes and canals, often where there are sheltered bays overhung
with trees and bushes. It also occurs on small slow-flowing rivers. In the
Scottish Highlands, S. metallica often breeds in similar habitat to C. aenea,
namely: ancient peaty lochs which usually contain white water-lily, bogbean
and marginal Sphagnum.
Breeding biology On finding a female, copulation takes place away from water in trees or
amongst low bushes and scrub. The female oviposits while hovering very low
down, repeatedly tapping her abdomen, two to three times per second, into
either wet Sphagnum moss or peat (both under and away from the water), or
directly into shallow water amongst tree roots or common reed. Oviposition in
S. metallica is discussed by Smith (1984) and Fox (1991). The larvae live
amongst peaty detritus and leaf litter, and probably take two or more years to
develop.
Flight periods S. metallica is on the wing from mid-June (occasionally earlier) to mid-August.
Status and distribution
European and world
distribution
In Scotland it can be seen with C. aenea, Aeshna juncea,
quadrimaculata and the commoner northern damselflies. In south-east
England the list includes most of the species to be found on mesotrophic
ponds and lakes. On slow-flowing rivers, it can be seen with Calopteryx
splendens and Platycnemis penmpes.
In Britain, S. metallica is divided into two distinct populations. One, in the
Highlands, is centred on Glen Affric and Glen Mor. The other, in England, is
much larger and includes the Weald of SusseX and west Kent, and the heaths of
Surrey, north Hampshire and Berkshire. The first fully documented record of S.
metallica in Britain was from Strathglass in 1869 by Dr Buchanan White
(McLachlan 1870). At the turn of the century it was still thought to be solely a
Scottish species by many leading entomologists (Lucas 1900), despite the fact
that Stephens (1835-37) had recorded it as 'rare in England: it has been found
in the metropolitan district in June'. It was first (re)discovered in England on 4
August 1908 at The Warren, near Crowborough in Sussex, by E R Speyer
(Speyer 1909). Considering that many of the entomologists of that period
were based in south-east England, perhaps S. metallica was indeed absent,
but one wonders whether, for example, the C. aenea recorded by C A Briggs
on 13 September 1891 at Bookham, Surrey, was in fact S. metallica, in view of
the exceptional late date. In 1922, S. metallica was found at Loch a' Chrion
Diore in Argyllshire by K J Morton (specimen in the Royal Scottish Museum),
and was refound there by E M and R W J Smith on 27 June 1995.
S. metallica occurs in central and northern Europe and east to the Volga and
Asia Minor. In the south of its range it is restricted to higher altitudes, such as
the Pyrenees and the Alps.
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