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Status and distribution
Anax imperator Leach Emperor dragonfly
Description The predominantly sky-blue abdomen and apple-green thorax of mature
European and world
distribution
males make this large robust hawker dragonfly unmistakable. The thoracic
coloration extends to segment 1 of the abdomen and to the sides of segment
2. A broad black mid-dorsal line, of uneven width, runs from segment 2 to the
end of the abdomen. The eyes are greenish blue. Females are similarly
patterned, but the mid-dorsal line is broader. The thorax and sides of the first
2 abdominal segments are apple-green as in the male, but the blue abdominal
coloration is usually replaced by dull green.
Habitat A. imperator breeds in ponds and lakes, including flooded sand and gravel pits
where there is rich marginal vegetation, and in dykes, canals and slow-flowing
rivers. Unlike some other aeshnids, they rarely breed in garden ponds - these
usually being too small. Adults can often be seen flying along a regular beat
over a lake, patrolling their territory, 2-3 m above the surface. They seldom
travel far from water.
Breeding biology A. imperator males are very territorial. There are rarely more than 5 per 100 m
of water's edge, and a small pond is never likely to have more than one male at
any one time, although many larvae may emerge from it (Moore 1964).
Copulation takes place away from water, sometimes in the tops of trees, and
lasts about 10 minutes. The female inserts her eggs into the tissues of
submerged plants. When flying from one oviposition site to another she often
bends the end of her abdomen downwards - a posture which usually prevents
males from attempting to mate. Most larvae emerge in their second year,
having spent their second winter in diapause in the last larval instar. They
have a synchronised emergence, sometimes in such large numbers that, if
there is a lack of unoccupied emergence sites (tall emergent vegetation,
bushes, etc), some larvae will emerge on top of others. However, some larvae
develop within one year; on occasion, these may make up the entire
population (Holmes & Randolph 1994). Under warm conditions, they emerge
in the evening, and usually make their maiden flight away from water in the
morning. Corbet (in Corbet et al. 1960) records predation of newly emerged
adults by blackbirds (Turdus merula) , whilst Khan (1983) records predation by
wood-mice (Apodemus sylvaticus).
Flight periods A. imperator is on the wing from early June to late August. It can be seen with
many other southern species of well-vegetated ponds, gravel pits and canals,
such as Aeshna grandis, Aeshna mixta, Libellula depressa and Orthetrurn
cancellatum.
A. imperator is widespread in southern England and south Wales, though it is
absent from the uplands of Dartmoor and the Brecon Beacons, and from the
chalk downland areas of Wiltshire and Hampshire. It has increased in numbers
in the northern part of its range in recent years. It has been found at several
new sites in Derbyshire created by local authorities in the 1980s as a result of
recreation and amenity schemes on former colliery sites. The recent increase
in records from Cheshire has culminated in breeding being proven in 1993 for
the first time. A. imperator is not reliably recorded from Ireland.
A. imperator has a very wide world distribution. Not only does it occur from
Portugal to Germany and east to the Middle East, Pakistan and central Asia,
but it is also found in much of northern and southern Africa and Madagascar.
It is absent from Scandinavia except for southern Sweden.
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