THE ESSEX SPECIES
Calopteryx virgo (Linne, 1758) Beautiful Demoiselle
Our two species of Calopteryx are large, spectacular damselflies. with tinted wings.
There should be no risk of confusing them with any other damselfly. However, the
separation of the two species from one another can sometimes be difficult. The densest
colouration of the wings is seen in the males of each species, which are quite easily
distinguished by the distribution of this colouration: concentrated in a large 'blotch' on
the outer half of each wing in C. splendens (the 'Banded' Demoiselle) and covering
almost the whole of the wing in males of C. virgo. Typically the colouration is dark,
smokey brown in C. virgo, and more metallic-blue in C. splendens, but this varies with
age. and is not a reliable character. The wings of the females are more delicately and
evenly tinted, usually green in C. splendens, and a reddish brown in C. virgo. The white
false pterostigma (the marking towards the tip. and on the fore-edge of each wing) is
twice as large on the forewing as on the hind wing in females of C. splendens, whilst the
difference in size is less marked in C. virgo.
Calopteryx virgo has always been very scarce in Essex, and should now be regarded as
an extreme rarity in our county. The species has a strongly southerly and westerly
distribution in Britain as a whole, with a very few scattered 'outposts' in the eastern
counties. The species breeds in swifter flowing rivers and streams (or in swifter reaches
of the same rivers) than does Calopteryx splendens, and prefers a sand or gravel-
bottomed water course. Longfield (Corbet. Longfield and Moore. 1985) also notes that
C. virgo favours tree-lined sites. Shady or dappled light conditions, such as are given by
willow plantations, do not discourage the adults, and they are to be found along such
stretches of river-side no less than more open reaches bordered by meadows. The
recorded flight period in Essex is from the last week in May to the second week in
August, but owing to the rarity of the species in our county this may be an
underestimate.
Doubleday (1871) reported C. virgo as common, 'flying in small streams', whilst
according to W. H. Harwood (1903). it was 'not uncommon near Birch Park". This is
almost certainly a reference to the Roman River, just south of Colchester, where it
occurs to this day. E. E. Syms (1929) included it on his list of Epping Forest dragonflies,
whilst E. B. Pinniger (1933) described it as 'not common' in the Forest. As with
C. splendens it may be that post-Doubleday sightings represent temporary extensions of
colonies on the Lee and Roding. Longfield (1949 b) referred to the occurrence of the
species on these rivers, but she noted that even in those restricted sites the species
appeared to be decreasing.
During the period of the current survey, the continued presence of C. virgo at
Harwood's old locality on the Roman River was indicated by the discovery of what were
thought to be C. virgo nymphs by Adrian Chalkley in 1981. The presence of the adults
was confirmed by myself in 1982, along the stretch of the Roman River including the
Roman River E.N.T. reserve. In 1983 the presence of the species still further up-stream
and on a tributary of the Roman River was established. This is. in my view, the only fully
confirmed breeding colony of C. virgo in Essex and it is. with one exception, the most
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