Dragonflies

British Dragonfly Society (BDS)

The Partnership acknowledges the BDS in publishing much of the information on this page.

However you might look upon them, it is true that they are a reliable indicator of good water quality, and recent research finds they can be useful for the biological control of mosquitoes.  They're also fascinating, beautiful and quite harmless - they have no sting and will not attack or bite.

It's not all good news, however.  Forty years ago the UK boasted 42 breeding species of dragonfly.  Three of these are now extinct.  The Orange-spotted Emerald was lost when a sewage spill polluted its last remaining breeding ground; the Norfolk Damselfly similarly surrended to local pollution; and the Dainty Damselfly was wiped out when its Essex habitat was flooded.

But thanks to a increasing awareness of the dragonfly's plight, to our expanding knowledge of their needs and conservation activity, several species are actually flourishing and partnership projects are helping this trend in the Bourne Valley.

Dragonfly or Damselfly?

Dragonflies belong to an order of insects known as the Odonata and in Britain they are classified into two sub-orders:

Dragonflies (Anisoptera) tend to be the larger of the two, much for robust and more powerful fliers.  The head is more spherical and consists almost entirely of a huge pair of eyes.  The front and back wings are dissimilar in shape and are normally held open whilst the dragonfly is at rest.

Damselflies (Zygoptera) are very delicate, slender insects, weak and fluttering in flight.  The head is rectangular and large eyes are positioned on either side, a bit like a hammerhead.  The front and back wings are the same shape and are normally held closed along the abdomen when the damselfly is at rest.

Where to find them

In Britain all dragonflies require permanent water and can be found in almost any conceivable wetland habitat, from ponds and lakes to canals, rivers, ditches and sphagnum bogs.

Dragonflies thrive in unpolluted water that supports plenty of submerged and emergent vegetation.  These provide egg laying and emergence sites as well as shelter.  Many species also require some open water.  They tend to prefer situations that are open to sunlight with some shelter from strong winds.

Eyesight

Dragonflies are visual hunters and have impressive vision being able to see in colour as well as ultraviolet light and polarised light, which enables them to see reflections of light on water.

Their large compound eyes are made up of as many as 30,000 facets or lenses (ommatidia).  Those in the upper part looking forward are usually larger and more numerous that those elsewhere providing the area of best visual acuity.  This is why dragonflies usually approach prey from behind and below.

Flight

Dragonflies are usually most noticeable when in flight, as the sunlight catches their wings and the iridescence on their bodies.  Sometimes they can be heard before they are seen when their wings catch the vegetation.

Hawker Dragonflies can fly at 36km/hour and Damselflies at 10km/hour.

Dragonflies are beautifully adapted for flight, having powerful flight muscles and wings that move independently.  They are incredibly agile and manoeuvrable and are able to hover, fly forwards, backwards, sideways and to rapidly change the direction and speed of flight.

Feeding

Both the larvae and adult dragonflies are voracious predators.

Adults feed on flying insects, especially small flies, midges and mosquitoes.  Some of the larger species, such as the Emperor, will take butterflies and damselflies.  Many species consume their prey on the wing, but some damselflies and chasers tend to rest while feeding.

Threats & Conservation

Over the last 40 years we have witnessed the extinction of three species of dragonfly in the British Isles and at least one third of the remainder are considered to be rare and localised.

The most significant threats appear to come from habitat destruction and fragmentation, pollution, inappropriate habitat management, alteration of site hydrology and the impacts of global climate change.

Dragonflies are worthy of conservation in their own right, but their requirements for clean water and a mosaic of habitats mean that if dragonflies are conserved so are many other organisms.  They can be used as a flagship not only for aquatic habitats but also for the wider insect world.

Bourne Valley species

More than 20 species of dragonfly have been recorded at the Bourne Valley SSSI, at least 18 with breeding evidence, and this reflects the variety of aquatic habitats such as acidic bog pools and vegetated ponds, and terrestrial feeding habitats.

Click on images to enlarge them

Species include: Keeled skimmer Orthetrum coerulescens Golden-ringed damselfly Cordulegaster boltonii Large Red damselfly Pyrrhosoma nymphula Small red damselfly Ceriagrion tenellum (nationally scarce) Downy emerald Cordulia aenea (nationally scarce) Black-tailed Skimmer Orthetrum cancellatum (local species) Click on the image to enlarge it Left: two Hawker dragonflies (probably Migrant Hawkers (Aeshna mixta)) in a mating wheel on bulrushes at the new fishing pond at Alderney Recreation Ground in early October. It's more usual to see this sort of behaviour during late summer, rather than Autumn.  Is this another sign of climate change?  Or simply an effect of this year's exceptionally mild weather?

Keeled skimmer at Bourne Valley SSSI Common Darter (female) on Bog Myrtle at Bourne Valley SSSI

In 2003 student Robert Aquilina carried out a study of local dragonflies, comparing numbers and species at the lagoons & wetlands created at Alderney (2000 & 2001) with more established ponds, pools and stream sites in the valley: A list of the species (excel file) can be found here The full report (MSc dissertation) is published here In 2005 a new study by Andrew Brown (Bournemouth University) and a colleague from the Herpetological Conservation Trust collected data on the status of Dorset's dragonflies, including those in the Bourne Valley.