The power of Jam-Jars: Pine Hoverflies return to the UK for the taste of jam
Recently, a magical, once in a lifetime story happened. In 2019, only 50 pine Hoverflies inhabited a lonely woodland site and were considered a critically endangered species.
Today, 30000 Pine Hoverflies have been released into the Cairngorms National Park, the last area that they survive in. Even better, they outnumber the people who live there by double.
How did this happen? The bigger question you have is, what do jam-jars have to do with conservation efforts?
The story
The pine hoverfly conservation programme was started in 2018. It involves the Rare Invertebrates in the Cairngorms, external (RIC) project, Pine Hoverfly Steering Group and local landowners – who started a breeding programme to rapidly increase the population.
When there’s only one area that these insects survive in, and inbreeding is a massive risk due to intense genetic homogeneity, how did they breed?
Jam-Jars
This is where the jam jars come into effect. Conservationists at the Royal Zoological Society of Scotland (RZSS) used jam jars and hummus pots to recreate the conditions that the hoverflies thrive in. In the wild: the larvae live in small holes that have rotted into old pine trees. Inside those holes they feed on a "nutritious soup" of bacteria, recreated by wood chippings from the pine trees mixed with rainwater.
This recipe is placed inside the jam jar and damp moss is used to plug the jar. This is how the RIC created a mini Earth for the endangered species. The temperature of their breeding area was also regularly checked so that their energy was used optimally for growth and development.
The RIC project doesn’t stop there. They strive to find out more about threatened invertebrate species and their distribution across the Cairngorms National Park. Conservation efforts involve the community to play their part, so they collaborate with landowners to protect and improve habitats.
Their efforts have not gone unnoticed, as the RIC is supported by the Scottish government's Nature Restoration Fund (BBC News, 2026).
Writen by Piedade Neves
REFERENCES
One of UK’s rarest flies returns to Cairngorms with the help of jam jars. (2026). BBC News. [online] 21 Apr. Available at: https://www.bbc.co.uk/news/articles/c248jqzvqp1o.
Rámon van Raaij (2024). Marmalade Hoverfly on Twig · Free Stock Photo. [online] Pexels. Available at: https://www.pexels.com/photo/marmalade-hoverfly-on-twig-21385211/
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