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 Bourne Valley SSSI

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 Did You Know?

Dragonflies

Dragonflies are among the most ancient of living creatures.  

From fossil records we know that these amazing insects were flying some 300 million years ago, before even dinosaurs roamed the earth.  

Over the centuries an extensive folklore has seen dragonflies revered in some cultures as symbols of strength, regeneration and pure water, and feared in others as shamanistic creatures with supernatural powers.

White-legged Damselfly (click to enlarge)

White-legged damselfly at the 

Alderney wetlands, 2003

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.

Here are some basic dragonfly facts - but there's a lot more information available from the British Dragonfly Society website.

Dragonfly or Damselfly?

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

Calopteryx Virgo, or Beautiful Demoiselle

Beautiful Demoiselle Damselfly

Coy Pond Gardens, June 2005

Click on photo for enlarged image

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.

Goldenringed c.Robert Aquilina

Golden-ringed dragonfly in the 

Bourne Valley

Dragonfly larvae are mostly ambush predators, feeding on anything that is smaller than them such as insect larvae, water fleas, snails, small fish and tadpoles.  They extend their modified lower lip (labium) at lightning speed and impale prey on the sharp mandibles.

Why they're Important

Their size and beauty make them especially valuable subjects for research into insect behaviour and ecology.  They have played a significant role in some cultures and they are increasingly being used as subjects for art (for example).

Dragonflies have aquatic larvae, which generally rely on good water quality.  Consequently they can be used to make rapid assessments of water quality and indicate a healthy ecosystem.

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.

Species include:

Click on images to enlarge them

  • 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)

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:

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.

Keeled Skimmer  Sarah Austin

Keeled skimmer at Bourne Valley SSSI

Common Darter (female) on Bog Myrtle  Sarah Austin

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

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 Bourne Valley Park 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?

 

For amazing dragonfly & damselfly photographs visit

Richard Ford's Digitalwildlife website

 

 

www.dragonflysoc.org.uk

British Dragonfly Society (BDS)

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

 


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