Science

Orkney’s Dragonflies

By theorkneynews on September 9, 2021 • ( Leave a comment )

“To-day I saw the dragon-fly
Come from the wells where he did lie.

“An inner impulse rent the veil
Of his old husk: from head to tail
Came out clear plates of sapphire mail.

“He dried his wings: like gauze they grew;
Thro’ crofts and pastures wet with dew
A living flash of light he flew.”

Tennyson

Odonate are any of an order (Odonata) of predaceous insects comprising the dragonflies and damselflies

There are eight resident species of odonate in Orkney:

four dragonflies (Four-spotted Chaser, Golden-ringed Dragonfly, Common Hawker and Black Darter)
four damselflies (Large Red, Blue-tailed, Common Blue and Emerald).

Graeme Walker is the British Dragonfly Society (BDS) area co-ordinator for Orkney and the dragonfly county recorder for the islands. These are his fabulous images of dragonflies and a damselfly more of which he posts on the Orkney Facebook page OrkOdo .

Graeme explained:

“Whilst we do see the occasional migrant or dispersive species, some from North Africa, these are few in number and at the mercy of prevailing weather conditions.

“Several of the species of concern for Britain and Ireland are doing quite well in Orkney. These are the three late Summer species: Common Hawker, Black Darter and Emerald Damselfly. In fact, the Emerald Damselfly is our most recent colonist, first noted in 2010 at Rackwick in Hoy and now widespread through Hoy and reported from Flotta, South Ronaldsay and East Mainland.

“However, the most immediate threats to all species in Orkney are habitat loss and climate change.

“Several consecutive dry Summers have led to many pools drying out which obviously has a detrimental impact on insect species which rely on freshwater for their aquatic larvae.

“Thankfully, the members of OrkOdo (the local Facebook page for dragonflies and damselflies), are out there during flight season, between May and October, reporting sightings and generating useful data for both local and national reports.”

What is happening across the British Isles and Ireland ?

Just published is the State of Dragonflies 2021. It is the first ever state of dragonflies report to be produced for Britain and Ireland.

‘State of’ reports have previously been produced for well-studied groups like birds and butterflies, and there have been other, similar reports revealing shocking declines in wildlife, both here and abroad. These indicate the profound effects inflicted on a wide range of species as a result of human activity on the planet.

The State of Dragonflies 2021 report converts half a century’s worth (1970-2019) of mostly ad hoc recording by dragonfly enthusiasts – that’s 1.4 million records from 17,000 observers – into trends. These dedicated citizen scientists have enabled researchers at the Biological Records Centre, part of the UK Centre for Ecology & Hydrology, to run occupancy-detection models that reveal significant changes in the fortunes of more than half of our 46 regular breeding and migrant dragonflies and damselflies.

No less than 19 species increased significantly (41%), whereas only 5 species (11%) declined overall in Britain and Ireland combined. A further 5 species increased and 3 species decreased in at least one of the constituent countries.

On the face of it, the results in State of Dragonflies 2021 might seem to be a good news story, but as ever the devil is in the detail.

In temperate areas like the British Isles, many flying insects, such as dragonflies, benefit as adults from hot weather – it improves their survival and helps them to find new breeding sites. So it’s not surprising that there are correlations with changes in the climate. With mobile adults and aquatic larvae, dragonflies are excellent indicators of the effects of climate change on wetlands.

Average temperatures have risen by almost 1 degree Celsius in summer during the last 50 years. This has allowed the generalist species, with less stringent habitat requirements, to colonise new areas, most notably by expanding their ranges northwards, with some colonising England from Continental Europe and others colonising Scotland and Ireland from England or Wales.

At the same time, it seems that some of upland and northern species are retreating. The reasons for this are less clear, but again most likely due to changes in the climate, coupled with habitat changes.

The largest decline recorded in the report came as a surprise – Emerald Damselfly. Graeme Walker noted in his comments that this is a recent colonist in parts of Orkney.

While climate undoubtedly does have a major influence on the distribution of insects in general, so too does the abundance and quality of the habitats where they live – which of course is wetlands in the case of dragonflies.

Three in every four ponds were lost in England and Wales in the 20^th century; many boggy areas were drained; and rivers have suffered pollution from agriculture and industry. That said, many ponds and lakes have been created in recent years and efforts have been made to clean up rivers and streams. Wetlands have also been recreated in former arable areas such as the Great Fen project in East Anglia, and peatlands have been restored after forestry, for example in the Flow Country in the Scottish Highlands.

Unfortunately, the ecological condition of most wetlands is poor and only those dragonfly species with a wide tolerance of water quality – the ‘generalists’ – have been able to take full advantage of new wetlands such as reservoirs, farm ponds and flooded mineral workings. In this way, many species have expanded their ranges and powerful fliers, such as Emperor Dragonfly and Migrant Hawker, have even been able to colonise Scotland and Ireland.

There have also been significant range expansions in the Red Listed Norfolk Hawker and Scarce Chaser, and localised species such as Red-eyed Damselfly and Hairy Dragonfly.

Since 1995, we have seen eight species reach Britain for the first time and at least two further species have reappeared after long absences. Six species have recently established breeding populations and another, Dainty Damselfly, has recolonised after being lost in the floods of 1953. In the case of Small Red-eyed Damselfly, which first appeared in 1999, the spread has been spectacular and it now occurs from County Durham to South Wales and Cornwall. More recently, Willow Emerald Damselfly and Southern Migrant Hawker have spread over much of south-east England.

Conversely, one former regular migrant, Yellow-winged Darter, an eastern rather than southern species, has declined, and occupancy has not changed very much among most of the resident ‘habitat specialists’, which are always going to be limited by their strict habitat requirements.