Brian Unwin, The Telegraph 11 Jan 08;
Dragonflies should be officially rated as key indicators of climate change in Britain after a decade of dramatic alteration in the status and distribution of some species.
That's the view of three experts who argue that these top-of the-range insects - which need warm weather to survive, hence their greatest diversity in tropical regions - can provide valuable evidence about rising temperatures and the impact on the environment.
"So much has happened to dragonflies in Britain since the 1990s that there is a most compelling case for the Government to adopt them as indicators of climate change", said Steve Brooks, a London Natural History Museum research entomologist with a special interest in the response of freshwater insects to climate change.
He teamed up with Adrian Parr, migration recorder for the British Dragonfly Society (BDS) and Peter Mill, the BDS chairman and retired Reader in Invertebrate Zoology at Leeds University, to make the point in a report published in the latest edition of the journal British Wildlife.
They point out that birds and butterflies have been adopted by the British Government as indicators of biodiversity and that the European Environment Agency proposes to follow this policy.
As a result their response to climate change is being monitored, but there are sound reasons why dragonflies are "at least as well suited" for the indicator role.
They stress that in temperate climates, adults require moderately warm conditions to enable flight and the rate of development of larvae under water is also affected by temperature. Frosts affect the larvae of some species, such as the small red damselfly (Ceriagrion tenellum), a factor limiting their northern distribution.
"Dragonflies certainly complement birds and butterflies, not least because a significant part of the dragonfly's life-cycle is completed in freshwater. Understanding the response of freshwater organisms to climate change complements the response of terrestrial groups," the report states.
"Nevertheless, adult dragonflies are strongly influenced by air temperatures, so dragonflies can provide an integrated response to climate change, reflecting both aquatic and terrestrial environments, a unique attribute when compared with butterflies and birds."
While the general trend has involved dragonflies that were previously unknown in Britain turning up and even colonising southern areas and existing residents expanding their range northwards, rising temperatures are not going to benefit all 39 breeding species.
Four of these species do not occur in southern Britain and are thought to be specially adapted to living in colder northern regions. Three of them - azure hawker (Aeshna caerulea), northern emerald (Somatochlora arctica) and northern damselfly (Coenagrion hastulatum) - are found only in Scotland.
Their distribution near the top end of the country means limited potential for a northward shift in response to milder weather so there is concern they may suffer range contraction.
Small red-eyed damselfly (Erythromma viridulum) provides one of the most vivid examples of distribution change. Previously unknown in the UK, the first recorded appearance was in Essex in 1999, and the species has since spread to many South East areas. It has been recorded through East Anglia north to The Wash and westwards across the Midlands.
Its range expansion, continuing a late 20th century northward spread in Europe, has been so rapid the report authors suspect it is not completely climate influenced.
"Most parts of southern and western Britain may already be suitable for it climatically.
"The rate of its initial expansion is more likely to be regulated by how rapidly it can colonise already suitable habitats. Once all suitable habitats are colonised, then we may see that its northern distributional limit is climate-related and further expansion slows down as it begins to track an expanding climate envelope."
Milder weather has enabled several formerly southern Britain-based breeding species to move into suitable habitats further north. Since 2001 two species, migrant hawker (Aeshna mixta) and emperor dragonfly (Anax imperator), have appeared in Ireland for the first time and two more, ruddy darter (Sympetrum sanguineum) and hairy dragonfly, (Brachytron pratense), have made north-west England debuts.
