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Status and distribution
Aeshna caerulea (Strom) Azure hawker
Description This is a medium-size hawker dragonfly, similar in body length to A. mixta. In
European and world
distribution
the mature male, the abdomen is black with an extensive pattern of mostly
paired blue markings on the dorsal surface of the abdomen. Unlike other
blue-spotted aeshnids, there are no green or yellow abdominal markings; thus,
A. caerulea can be distinguished from the larger, and much commoner, A.
juncea which can occur in the same localities (however, close examination is
necessary as this difference is not obvious in flight). The antehumeral stripes
on the brownish black thorax are thin or absent, and there are a pair of narrow
pale stripes on the sides of the thorax. Females are browner, and also have a
pattern of paired markings along the abdomen, but these vary from dull beige
to lavender-blue, as in immature males, and, exceptionally, are pale whitish or
bright blue (D J Clarke, pers. comm.).
Habitat A. caerulea breeds within large open moorland areas in shallow bog pools
with at least some marginal Sphagnum moss, at altitudes ranging from near sea
level to 550 m (Clarke et al. 1990). Males of A. caerulea often sun themselves
on whitish boulders, the white trunks of birch trees or on pale moss hummocks
of Racomithum lanughosum. The close proximity of woodland areas is not an
essential feature of A. caerulea breeding sites.
Breeding biology There is doubt about whether this species is territorial. Eggs are laid into soft
peat or Sphagnum moss in shallow bog pools of up to 30 m2 surface area, and
water depth of 20 cm over a further 20 cm of peaty mud, although smaller
pools are usually selected (Clarke et al. 1990). Oviposition lasts up to three
minutes at any one place, and occurs only during periods of sunshine. The
eggs pass the winter in diapause, and the larvae probably take three years to
develop, but captive breeding experiments suggest that there may be
considerable variability (Clarke 1994). Emergence has been observed on the
stems of common cottongrass and of over-hanging heather.
Flight periods A. caerulea is on the wing from the beginning of June, occasionally earlier, to
mid-August. Other species which are lmown to breed in the same general
area are Pyrrhosoma nymphula, A. juncea, Somatochlora arctica, Leucorrhinia
dubia, and Libellula quadrimaculata.
The first appearance of A. caerulea on the British list stems from a specimen
taken in northern Scotland and given to Sélys-Longchamps by a Mr Wilson in
1845 (Corbet et al. 1960). Its position as a British species was enhanced by R
McLachlan's discovery of it at Rannoch, Perthshire, in June 1865 (McLachlan
1865). It is a scarce dragonfly in Britain, restricted to northern Scotland and
Galloway. It seems to have been recorded more frequently in the past, and has
probably suffered in some areas from the increase in conifer planting and the
drainage which that entails. However, it may easily be overlooked. It has not
been recorded from Ireland, although there appears to be suitable habitat.
A. caerulea is a boreo-montane species, and is found from north Scotland and
north Scandinavia to arctic Russia. There are relict populations in the Alps and
other mountain areas of central Europe and the Caucasus.
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