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Dorset’s dragonflies

Mark Burrows is bewitched by the beauty of Dorset’s deadly four-winged predators and their locations

Female migrant hawker

Female migrant hawker

Dazzling flying insects display flamboyant aerobatics every year near Dorset’s ponds, lakes and rivers. Decked out in intense colours, dragonflies are masters of both vision and manoeuvres on the wing. They are also the James Deans of the insect world: they live fast, die young and leave good-looking corpses.
When not roosting motionless on a favourite perch, they are hunting for food, searching for mates or chasing off competitors, all at top speed. This is the life of an imago (the final stage of an insect’s life) after spending up to four years stalking prey under water as a cumbersome if equally murderous nymph. Their veined wings are propelled by a mechanism more akin to those of birds or bats than of other insects, amongst which dragonflies are unique in using their heads as balancing devices. Damselflies apart, the closest relatives of these living fossils are mayflies.
Dragonflies have been around 1500 times longer than man. Way before dinosaurs roamed the planet, dragonflies ruled the air during the carboniferous period, some 300 million years ago. They were monsters compared with today’s models; they attained wingspans of over two feet in the oxygen-rich atmosphere. Without any flowering plants back then, the towering horsetails, ferns and scale trees provided roosting opportunities. Dorset County Museum possesses part of a fossilised dragonfly. Discovered near Swanage and dating back 142 million years, its size is similar to today’s species.
It is the geology of Dorset combined with the vestiges of mineral extraction and of human combat that dictate the areas where dragonflies are most likely to be seen. Vast swathes of the terrain consist of highly porous chalk or limestone. In such areas there are few permanent ponds. Elsewhere, plenty of the rivers and streams flow too fast for our species, although here and there slacker watercourses provide ideal habitats for egg-laying and nymph survival.
It is areas of heathland that have become significant population strongholds for dragonflies. Formerly bereft of contained water bodies, they now feature many small pools mostly created by the extraction of clay. The nature reserve at Arne, is part of the Poole Basin that covers nearly thirty per cent of the county. Once almost entirely heathland, it sits not only on sands and chalk but, crucially for bog pool creation, on clay.

An immature female migrant hawker

An immature female migrant hawker

Some drainage ditches dug on land to sustain farming can also hold water all year, and it is these factors that have resulted in the Poole Basin providing Dorset’s most prolific dragonfly habitats. Despite the damage inflicted by industrial and agricultural pollution, it is also our activity, whether intentional or not, that has sustained if not boosted dragonfly populations in modern Dorset.
Arne, experiencing post-war dragonfly population explosions, hosted assorted field studies during the mid-1950s. Among the objectives was an attempt to determine if dragonflies have homing tendencies towards specific ponds where they had first dwelt as nymphs. 119 mature dragonflies were netted from two bomb-crater ponds 150 yards apart and carefully marked with a harmless dye before being transferred to the other pond for release. Forty-two were subsequently discovered frequenting the pond where released, two were discovered in an altogether different location, but none had returned to its site of capture.

Bomb-crater pond at Arne

Bomb-crater pond at Arne

Of the breeds rarer here, the scarce chaser prefers pristine, slow-moving waters like those afforded by the conjoining Stour and Moors rivers or the Frome further south. Golden-ringed dragonflies favour shallow streams for breeding, and black darters are unlikely to be spotted away from the acidic bog and stream waters of the Poole Basin, where Christchurch Common provides favourable territory. By contrast, ruddy darters require marshland habitats of lower acidity.

Male common darter

Male common darter

The brown hawker, while not a rare species, is much more likely to be found in the east of the county. Another infrequently seen hawker – the smallest – is the hairy dragonfly. Slow-moving ditches and streams around Christchurch and the periphery of the Poole Basin during early summer offer the best hope of seeing specimens. Sadly, the orange-spotted emerald has become extinct in large parts of Western Europe; the Moors River is infamous among enthusiasts as being the last location in Britain where an orange-spotted emerald was recorded back in 1957 before being wiped out, most probably by pollution.

Emperor emerging from nymph in our  garden pond at around midnight last summer

Emperor emerging from nymph in our
garden pond at around midnight last summer

At a glance, the territory-dominating emperors are Dorset’s largest dragonflies, followed by the equally dynamic hawkers. Golden-ringed females, however, just about have the longest bodies. Emperors are common across the county, while common hawkers are ironically sparse compared with the more colourful and inquisitive southern hawkers that are familiar in the Poole Basin and around Weymouth. The smaller migrant hawkers may well be the most plentiful hawkers in many of Dorset’s coastal-hugging areas, where they first established breeding populations after arriving from continental Europe. Their range has since expanded, notably westward along the river Stour.

Male southern hawker

Male southern hawker

The early summer chasers are mid-sized with a discernibly broad, flattened abdomen. Broad-bodied chasers can be found all over the county, while four-spotted chasers tend to inhabit sites in Purbeck and towards the New Forest. These are also the more likely locations for spotting keeled and black-tailed skimmers, which are relatively squat, but smaller than chasers. Slenderer and smaller are emeralds, of which the copper-imbued downy emerald is restricted to a few locations clustered around the Poole Basin. The smallest species are the spindly darters.
Dragonflies tend to have a favourite perch where they return after each flight, and darters, inclined to hover close to the ground, prefer resting there or on low perches. The common darter is widely distributed across the county and may be confused with the ruddy darter.

River Stour at West Parley where, amongst others, the hairy dragonfly was spotted last year

River Stour at West Parley where, amongst others, the hairy dragonfly was spotted last year

 

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