22 Aug 2023

We’ve become the first in Europe to successfully breed a critically endangered stonefly – 28 years after it had been declared extinct!

Our staff were called in by Buglife Cymru to start an emergency breeding effort for the critically endangered scarce yellow sally stonefly. This was part of a rescue mission to save the species from extinction following its rediscovery in the River Dee, North Wales.

Having not been recorded since 1995, two small populations were found in the river, and believed to be the only remaining location for the stonefly in the UK.

In 2022 we joined with conservationists from wildlife charities Buglife Cymru and The Welsh Dee Trust, as well as freshwater invertebrate specialist John Davy-Bowker, and set about sampling and carefully collecting a small number of the stoneflies from the areas where they were rediscovered.

Thirty of the insects were carefully transferred to a special behind-the-scenes facility here at the zoo where a dedicated team of specialists set about meticulously studying the insect during its lifecycle. Experts believe it to be the first time ever that the species has been successfully bred and reared through its complete lifecycle in a zoo setting.

“When just 30 scarce yellow sally stoneflies arrived at the zoo, the scientific data on the species was extremely limited. They were so few in number and, living for a period of just four to six weeks as adults, we really had no room for error in our efforts to save them. We had to learn as much as we could, as quickly as we could, to help them back from the brink.”

Joe Chattell, Aquarist at the zoo.

Joe continued to say:

“We’ve been able to record and document every tiny detail about the stoneflies and their larva in our specially created breeding facilities. This process began by replicating their wild environment, which is highly-oxygenated water on the riverbed caused by water passing over cobbles. We then tweaked the lighting and temperature conditions each day to mimic a normal 24-hour cycle, while also including seasonal variations. A lot of intricate work goes into saving a tiny insect from extinction.

“In just a few weeks we were able to understand the species and its lifecycle, breeding patterns and favoured environment. Everything we have learned so far, including every slight tweak we made, has been meticulously recorded and given us a detailed blueprint. We hope this work will set the foundations for a conservation breeding programme for the critically endangered insect, all while helping to further increase the small surviving population in the River Dee.

“We’re enormously proud to be the first zoo to successfully breed this special stonefly with our partners, Buglife Cymru who are safeguarding the species and its future here in the UK.”

We now hope our species-saving efforts will go on to secure additional long-term funding for a conservation breeding programme to help further boost the wild population of stoneflies in the River Dee.

Clare Dinham, Wales Manager at Buglife Cymru, added:

“I’m very pleased to confirm that funding for the delivery phase of ‘Natur am Byth!’ has been awarded by National Lottery Heritage Fund. As part of this programme, the scarce yellow sally stonefly project will carry out further surveys for the species along the Dee, helping to inform future conservation efforts over the next four years, which may include re-introductions to areas where it has historically been recorded.

“We were thrilled when Chester Zoo came on board as a partner in the project. They’ve achieved amazing results with their conservation breeding efforts, providing unique insights into the ecology and behaviour of this iconic Welsh species. We’re looking forward to working with them over the next four years on this exciting project.

“This species is highly vulnerable to habitat loss, pollution incidents from sewage and litter, as well as climate change. The stoneflies need highly oxygenated, clean water to thrive so it’s important that their habitat in the River Dee is protected – especially as it’s currently the only known location in the UK for this species.”

The scarce yellow sally stonefly is a critically endangered species that was first identified in the River Dee in 1959 and was regularly recorded up until 1995 when subsequent surveys failed to locate any living populations in the UK. The species was presumed to have gone extinct in the British Isles – while a small number of populations were diminishing across Eastern Europe.

This work was made possible by National Lottery players through a Heritage Fund development grant to the Wales-wide conservation partnership Natur am Byth.

Check our the other amazing conservation projects we’re involved in, here at the zoo and across the globe! We endeavor to do everything we can to make sure that wildlife around the world thrives.