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Cordulia aenea (Linnaeus) Downy emerald
Description C. aenea is one of three surviving corduliids found in Britain, and one of two from
Ireland. They are dark medium-size dragonflies with a metallic sheen to their
bodies. In C. aenea, the thorax is metallic bronze-green with a dense covering of
buff-coloured downy hairs. The abdomen is dark greenish black with bronze
reflections, and is slightly club-shaped in males. There are pale yellow markings
on abdominal segments 2 and 3 laterally and ventrally. The eyes are green, and
there is a small amber area at the base of the wings. C. aenea resembles both
Somatochlora arctica and S. metallica, but there are distinctive differences in the
yellow facial markings and in the shape of the anal appendages.
Habitat C. aenea breeds on well-vegetated mesotrophic, neutral to mildly acidic ponds,
lakes and canals often where there are shallow, sheltered bays with trees and
bushes overhanging the water margin. In Hampshire and Surrey it has also been
recorded from slow-flowing streams and small rivers. In the Scottish Highlands and
in Ireland, the breeding sites are relatively open along the water margin, although
woodland is often in close proximity (Caledonian pinewoods or Killarney
oakwoods, respectively). These sites are small peaty lakes in low heather
moorland containing white water-lily, bogbean and additionally, in the Highlands,
marginal Sphagnum and sedges (slender sedge, bottle sedge and bog-sedge)
and, in Ireland, marginal great fen sedge.
Breeding biology C. aenea patrol the edges of water bodies with a characteristic rapid flight
interspersed with short periods of hovering. They hold the end of their abdomen
slightly higher than the thorax in flight, giving a distinctive appearance. They are
aggressive, and the length of a beat depends on the number of males present. The
theoretical optimal length of the patrol beat has been calculated by Ubukata (1986)
and corresponds with field data for C. aenea amurensis (8-10 m when other males
are present, 20-60 m when they are not) (Ubukata 1975). After copulation, usually
in nearby trees and bushes, the female oviposits, unaccompanied by the male, by
repeatedly dipping the tip of her abdomen into the water while in flight, often in
the shadier parts. About ten eggs are released with each dip. These are
gelatinous and stick to submerged vegetation. They soon hatch, and the larvae,
which live amongst bottom debris, probably take two to three years to develop.
Flight periods C. aenea is on the wing from late May to late July. In the Highlands, it may be seen
Status and distribution
European and world
distribution
with S. metallica, Aeshna juncea, and Illbellula quadrimaculata, whilst further south,
in Argyllshire, it occurs with Brachytron pratense and Aeshna cyanea. In southern
England, its breeding sites may contain all these species plus Erythromma najas,
Anax imperator, Libellula depressa, and others.
The earliest record appears to be from Hampstead, Surrey, where Donovan took it
in 1805 (Longfield 1949b). Today it is widespread in suitable habitat in the Weald
and on the heaths on the Surrey/Hampshire border. It is not uncommon in the New
Forest area and the Dorset heaths, but elsewhere it has a very scattered
distribution — from Newton Abbot in Devon to Glen Affric in the Highlands. The
presence of C. aenea at isolated sites probably represents relict populations from
an earlier period. In Ireland, C. aenea was first recorded by a Mr Hely, in a letter to
Holiday in 1838, at Killarney, Co Kerry (King & Halbert 1910), but it appears that
this record was disbelieved. It was found again in the Killarney area by E Bullock in
1923 (Graves 1947), and still breeds at a few sites there today These are within the
Killarney National Park and so receive some protection. Elsewhere in Ireland,
several individuals were found in the forest at Glengarriff, Co Cork, on 14 July 1978
(Goyvaerts 1979), but a breeding population has yet to be located. On 23 May
1992, several C. aenea were discovered at a site near Ballinaboy, West Galway, by
M Ticlaier (B Nelson, pers. comm.).
On the continent, C. aenea occurs from France through central and northern
Europe to Siberia and Japan. It is absent from the Iberian peninsula, most of the
Mediterranean area, and much of northern Scandinavia.
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