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A male black-winged dragonfly rests on a grass leaf near the town of Klina, Kosovo, on July 12.ARMEND NIMANI/AFP/Getty Images

Scientists often measure the impact of climate change by monitoring glaciers, tracking temperature changes and recording extreme weather conditions. But a group of naturalists in Britain has found a new yardstick: watching dragonflies.

A report based on 50 years of studying dragonflies and their close relative, damselflies, has found that warming temperatures has allowed the flying insects to spread across the U.K. and Ireland at a remarkable rate, and some species are now regularly spotted as far north as Scotland.

“Being cold-blooded insects, dragonflies are very susceptible to changes in their environment,” said Eleanor Colver, a conservation officer with the British Dragonfly Society (BDS), which conducted the research. “Historically in the U.K, we haven’t had a great diversity of species. But as the climate is warming, it’s becoming warm enough for species which are traditionally found in warmer areas in the south of England or even on continental Europe to move up north.”

Released this week, the report is derived from the work of 17,000 dragonfly enthusiasts who have dutifully recorded the movements of the insects since 1970. An analysis of the records found that 19 of Britain’s 46 dragonfly and damselfly species have significantly increased their range, and eight new species have arrived in the U.K. from other parts of Europe.

Dragonfly diversity in

Britain and Ireland

Number of dragonfly species

1

5

9

13

17

21

25

29

33

All records up to

and including 1990

Durham

London

All records up to

and including 2000

Durham

London

All records up to

and including 2010

Durham

London

All records up to

and including 2019

Durham

London

SOURCE: BRITISH DRAGONFLY SOCIETY

Dragonfly diversity in Britain and Ireland

Number of dragonfly species

1

5

9

13

17

21

25

29

33

All records up to

and including 1990

Durham

London

All records up to

and including 2000

Durham

London

All records up to

and including 2010

Durham

London

All records up to

and including 2019

Durham

London

SOURCE: BRITISH DRAGONFLY SOCIETY

Dragonfly diversity in Britain and Ireland

Number of dragonfly species

1

5

9

13

17

21

25

29

33

All records up to

and including 1990

All records up to

and including 2000

Durham

Durham

London

London

All records up to

and including 2010

All records up to

and including 2019

Durham

Durham

London

London

SOURCE: BRITISH DRAGONFLY SOCIETY

The increased range has coincided with a rise in temperature, the report said. Average temperatures in the U.K. and Ireland have risen by almost 1 degree Celsius in summer during the last 50 years, and by 0.6 of a degree in winter.

Since 1970, “nearly four times as many dragonfly species have increased their distribution than decreased within Britain and Ireland,” said Pam Taylor, who co-authored the report. “The main factor behind these gains and observed trends is climate change, although habitat changes have also played their part.”

The biggest winner has been the emperor dragonfly, one of the largest types of dragonflies, which has green colouring for females and blue for males. They used to be confined to southern England, but have been moving westward and northward since the 1990s. The species crossed over to Ireland in 2000 and has been regularly sighted in Scotland since 2003, the report said.

Another species, the dainty damselfly – which is blue and black in colour – vanished from the U.K. in the 1950s after severe coastal flooding. They made a return to the U.K. from northern Europe in 2010 and have been expanding across Kent since 2019, the report notes.

“It’s not just a British phenomenon – it’s happening all over the world,” said Dave Smallshire, another co-author of the study. “Certainly in North America, you’ve got the same sort of thing happening with southern species moving northwards.”

Mr. Smallshire, 70, has been studying dragonflies for 40 years and has seen the changes firsthand. “When I used to live in the midlands of England, there were certain species that we didn’t see,” he said from his home in Devon, in southern England. “And then all of sudden, they were there. And now these species are in Scotland. They jumped half a country, basically, in 30 or 40 years.” He noted that the small red-eyed damselfly first appeared on the Isle of Wight in 2000 and is now seen across southern England, Wales and as far north as Durham. “That’s an astonishing spread,” he added.

Emerald Damselfly occupancy

in Britain and Ireland

Proportion of the geographical area in which

emerald damselflies were present in each year

100%

75

50

25

0

1970

1980

1990

2000

2010

2020

SOURCE: BRITISH DRAGONFLY SOCIETY

Emerald Damselfly occupancy

in Britain and Ireland

Proportion of the geographical area in which

emerald damselflies were present in each year

100%

75

50

25

0

1970

1980

1990

2000

2010

2020

SOURCE: BRITISH DRAGONFLY SOCIETY

Emerald Damselfly occupancy in Britain and Ireland

Proportion of the geographical area in which emerald

damselflies were present in each year

100%

75

50

25

0

1970

1980

1990

2000

2010

2020

SOURCE: BRITISH DRAGONFLY SOCIETY

Not all of the news has been positive. Dragonflies and damselflies – which are smaller and fold in their wings along their abdomen when resting, while dragonflies keep theirs stretched out – tend to thrive in lakes, ponds and slow-flowing sections of rivers. Drought and the destruction of habitat has led some less hardy species to reduce their range. The report said that five of the 46 species observed have experienced a significant decline in how far they travel.

For example, the emerald damselfly, which favours small ponds and shallow bogs, has been found in fewer locations since the 1990s. The report said rising temperatures could be drying out such areas earlier each year, leading to the destruction of some populations. “It is also likely that pond restorations, which often favour other species of damselfly, could be detrimental to this species,” the report added.

Some other insects have also not fared as well. The report said that while moths have increased their range over the past 50 years because of climate change, the abundance of most moth species has fallen because of a loss of habitat. Several types of butterflies have also spread further across the country, but 70 per cent of butterflies that require a specific type of habitat have reduced their range.

The BDS is hoping to provide another overview of the dragonfly and damselfly population in five years, and Ms. Colver said researchers will be studying whether some species are able to adapt more quickly to climate change.

“We now know where they are, but we don’t know why they are there,” she said. “There’s a lot of different factors that we need to untangle.”

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