City bumblebees have been found to grow healthier colonies than those in the surrounding suburbs and countryside. They may be taking advantage of humans’ preference for flowering plants around businesses and homes.
“There are a few species that are really able to exploit the urban environment – pigeons, rats, foxes. It seems like bees belong to that group,” says Ash Samuelson at the Royal Holloway University of London.
She and her team raised colonies from wild-caught bumblebee queens, and placed them in 38 spots in areas with different degrees of urbanisation – inner-city London, surrounding suburbs, and rural farmland in southeast England. They tracked the size of the eventual colony, and the amount of pollen and nectar the bees stored.
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Both the village and city colonies produced a significantly higher number of offspring than the countryside bees. Samuelson says this suggests that queen bees in the cities and villages lived longer and were able to build up a larger troupe of worker bees.
“Cities can be very good resources for bees. There are gardens and parks that have a lot of flowers available all year round,” she says. “In agricultural areas, you have mass crops that provide flowers only for a short-lived period.”
Enjoying the parks
The bees that lived among the crops stored less food – an indicator of colony strength – than their city counterparts.
“It’s important to keep those stores available for rainy days when they can’t collect any more,” says Samuelson. “When we see low stores, that suggests low food availability – they’re just eating as much as they can get.”
Farmland also tends to be sprayed with pesticides that can harm bees. Lower exposure in the cities could be a factor here as well, she says.
Robert Paxton at Martin Luther University in Halle, Germany, says he sees a similar trend in his work, where he found that bumblebees pollinate flowers at a higher rate within cities than in agricultural areas.
Using wild bees ensures that the study takes into account adaptations made possible by the genes of this particular species, Bombus terrestris, says Scott McArt at Cornell University in New York. But he says the trend shown here isn’t global. In North America, he says, bumblebees tend to do better in agricultural areas.
“Maybe people in the US aren’t planting as many flowers in their gardens, or there aren’t as many bee friendly green spaces in urban areas,” says McArt.
