London’s skyline is filled with tall buildings, and many of them are far greener than you might expect. Rooftop gardens have become a common feature in the city. These spaces are important not just for people who work in and around them, but also for wildlife. Pollinators have been found as high as the 14th storey, showing how adaptable they can be in urban environments.
As of 2022, there are 121 buildings or structures over 100 metres tall in Greater London, with 24 of these located in the City of London. With so many rooftops now hosting gardens, it would be interesting to know whether pollinators able to move between them. Curious to find out more, Pollinating London Together worked with BNP Paribas and Royal London to run a small pilot project to see whether pollinators were travelling between rooftops. To test this, we did a simple mark and recapture exercise.
On a single summer’s day, three members of the PLT team, Konstantinos, George, and Joris, spread out across three sites: 80 Fenchurch Street, the Garden at 120, and Aldgate School. Armed with nets and marking tubes, they carefully caught pollinators, marked them with a tiny dot of coloured paint, and released them back onto the flowers unharmed. Each rooftop had its own colour, so if an insect turned up somewhere else, we could tell where it had first been caught. Three bees that were originally marked at 80 Fenchurch Street later appeared at Aldgate School, suggesting that pollinators do indeed move between rooftops. While the experiment only ran for a single day, this was an exciting sign that the aerial green spaces of the city are possibly not isolated but connected by pollinator flight paths.
In addition to movement between rooftops, the team also recorded which species were present at each site at the time. There appeared to be a difference in diversity depending on height. The Garden at 120, the highest of the three sites, was dominated by honeybees. At 80 Fenchurch Street, a little lower down, honeybees were also common, but the team also observed some more bumblebees, smaller solitary bees and hoverflies. The most diverse community of pollinators was found at Aldgate School, the lowest rooftop in the project.
The above image shows a tiny metallic green furrow bee marked at 80 Fenchurch during the experiment.
Although the experiment was small in scale and cannot be used to identify firm trends, it provides valuable insights. It suggests that rooftop gardens at different heights may support different pollinator communities, and that pollinators are capable of linking green spaces across the city.
For Pollinating London Together, this project highlights the importance of continued collaboration between businesses, schools, and conservation groups. Even one-off experiments like this can spark new ways of thinking about how London’s rooftops can support pollinators, and how we can better understand the hidden networks that keep our city buzzing.
