Urban areas are a surprisingly rich food reservoir for pollinating insects such as bees and wasps, according to a UK study published in the Journal of Ecology.
Home gardens are particularly important, the study found, accounting for 85% of the nectar – sugar-rich liquid that provides pollinators with energy – within towns and cities and the most diverse supply overall.
Results showed that just three gardens generated on average around a teaspoon of the liquid gold – enough to attract and fuel thousands of pollinators.
“This means that towns and cities could be hotspots of diversity of food – important for feeding many different types of pollinators and giving them a balanced diet,” says lead author Nicholas Tew, from the University of Bristol.
“The actions of individual gardeners are crucial,” he adds. “Garden nectar provides the vast majority of all. This gives everyone a chance to help pollinator conservation on their doorstep.”
Pollinators include bees, wasps, butterflies, moths, bats and beetles. They are critical for ecosystems and agriculture as most plant species need them to reproduce, and research suggests their survival relies especially on the diversity of flowering plants.
To explore how our sprawling urban areas could support them, Tew’s research group previously led the Urban Pollinators Project in collaboration with other universities. They found that cities and gardens – community and private – are vital for pollinators, leading them to question how to quantify and harness this resource.
“The gap in our knowledge was how much nectar and pollen urban areas produce and how this compares with the countryside,” Tew explains, “important information if we want to understand how important our towns and cities can be for pollinator conservation and how best to manage them.”
So, for the current study, Tew and colleagues measured the supply of nectar in urban areas, farmland and nature reserve landscapes, and then within four towns and cities (Bristol, Edinburgh, Leeds and Reading) to determine how much nectar different land uses produce.
To do this, they extracted nectar from more than 3000 flowers comprising nearly 200 plant species using a fine glass tube and quantified it using a refractometer, an instrument that measures how much light refracts when passing through a solution.
Then they sourced nectar measurements from other published studies and combined the nectar-per-flower values with numbers of flowers from each species in different habitats as previously measured by the group.
Overall, nectar quantity per unit area was similar in urban, farmland and nature reserve landscapes. But urban nectar supply was most diverse, as it was produced by more flowering plant species. And while private gardens supplied similarly large amounts per unit as allotments, they covered more land – nearly a third of towns and cities.
It’s important to note the findings are specific to the UK, and maybe parts of western Europe, Tew says. Most urban nectar comes from ornamental species that are not native, which can be attractive to generalist pollinators but may not benefit specialist species that feed from selective native flower species.
Thus private gardens in other regions might have different benefits. Australia, for instance, has more endemic species and specialist pollinators than the UK, so while non-natives would still provide some benefit, natives may be more important overall.
Most recommendations for attracting pollinators in Australia include supporting native bees and other local specialists. Suggestions include planting more native species and providing accommodation for native bees, most of which are solitary species – unlike the familiar, colonial European honeybee.
But in general, Tew says home gardeners can all support biodiversity with some key strategies, especially planting as many nectar-rich flowering plants as possible and different species that ensure flowers all year round.
Other recommendations include mowing the lawn less often to let dandelions, clovers and other plants flower, avoiding pesticides and never spraying open flowers, and covering as much garden area as possible in flowery borders and natural lawns.