The Norfolk Hawker (Aeshna isoceles) is a small hawker dragonfly that is rare in Britain. It has a brown colour with green eyes and clear wings and also a yellow triangular mark on the second abdominal segment which gave rise to its scientific name.
A. isoceles is one of only two brown hawkers found in Europe. Both have a brown thorax and abdomen but A. isoceles has green eyes and clear wings and a diagnostic yellow triangular mark on the second abdominal segment. The hindwings have a amber patch at their base. In contrast A. grandis has yellowish wings and blueish eyes. The green eye of A. isoceles stand out even in flight and in practice it is not difficult to tell these two dragonflies apart. In addition to the morphological differences A. isoceles is on the wing much earlier in the year than A. grandis.
Distribution and habitatEdit
A. isoceles is found in central Europe and around the Mediterranean and, the lowlands of North Africa. It is more common in eastern Europe than the south western Europe; it occurs in Spain and Portugal but is local.It is found wet areas, ponds, ditches and marshes, with dense vegetation and, in studies carried out in England, was found to be associated with Water-soldier (Stratiotes aloides).
Status in BritainEdit
The Norfolk Hawker has always been a scarce and local insect in Britain. It used to be found in the Cambridgeshire fens but by the early 1980's the populations had greatly declined. It is now confined to relatively unpolluted fens and grazing marshes in the Broadlands of Norfolk and north-east Suffolk. It can be found in Hickling Broad and two National Nature Reserves: Mid-Yare NNR and Ludham - Potter Heigham NNR. It is protected under Schedule 5 of the Wildlife and Countryside Act 1981 and listed in Category 1 (endangered) in the British Red Data Books on Insects.
It is one of the earliest Aeshna dragonflies to be on the wing with a flight period from May to August. Adults do not spend as much time on the wing as other Aeshnas. Males will fly around over a stretch of water defending a territory and if the pond is small the male will hover over the centre of the pond. Unlike other aeshnas, where the adults seem to be continuously on the wing beating up and down their territory, male A. isoceles come to rest on vegetation from time to time. Females oviposit onto plants and the eggs hatch in about 2 weeks. Larval development takes 2 years.