Macrocosm: Bumblebees Make Use of Cracks in Infrastructure

Kimberly Hosey

Bees need nature, not concrete, which leads many to believe that cities and bees go together like water and honey.

But ecologists from the University of Akron have found that, though it’s not ideal, bees can forage and find habitat in small weedy patches in Midwestern cities.

The study, published in Urban Ecosystems in February 2020, looked at bee and flower distribution within weedy plots in six industrial cities in the Midwestern USA, categorized as ‘shrinking cities’ by the researchers. These cities have all experienced sharp population declines in a very short period as residents left to pursue larger cities or smaller suburbs, leaving wide spaces of abandoned business lots and untamed sidewalks behind.

These areas of cracked concrete allow for weeds to spring up and for bees to make a home. The study found that areas of high development and areas of low development had a very similar concentration of bees, markedly changing the way scientists look at urban spaces and their relation to struggling, yet essential pollinators.

Why do we like pollinators?

Pollinators are vital parts of any ecosystem. They are required for reproduction by 85% of flowering plants, and approximately 35% of crop species. Generalist pollinators, such as the bumblebee, are among some of the most treasured, with their ability to shake down the small reproductive organs on a wide array of plants and their tendency to hop between flowers of the same species.

Bumblebees were first placed on the federal endangered species list in 2017 after an estimated 87% population loss over the last 20 years, which was attributed to overuse of pesticides, introduced parasites and pests, and habitat loss.

Urban planners often feel the pressure from environmental groups to create community gardens or other green spaces for these threatened pollinators, pumping vibrancy into the slate-grey foundations of their cities. But there may be a new way to green-ify, as well as a reason to not immediately spray down invasive weeds.

Plots of scraggly flowers that push through the corners of sidewalks and underpasses provide important resources to the pollinators buzzing around in Midwestern cities. Though the study looked at several different types of bees, the happiest pollinator within these margins is the bumblebee.

Bumblebees, unlike some other pollinators, have multi-generational family units, complete with babysitters. This allows for the bumblebees to forage far away from home for hours at a time, trusting in their fellow drone that the hive will stay safe. 

They are larger than other insects, allowing them to ‘hop’ further distances between sparse flowers, but their colonies are small. This small colony size allows them to fit snugly into cavities too tiny to be used by other eusocial bees. 

The bumblebee has, in many ways, squeezed itself into even the most hostile urban environments.

The most striking fact from this study was not that bumblebees could survive in urban spaces. Scientists and city-dwellers have known that for years, watching their fat, fuzzy bodies trail around the sky like lazy dandelion seeds. The importance of this study was showing how well the bumblebees could survive in these environments.

Paige Reeher, the lead author of the study, said that though it’s not as good as a hive in a national forest, the city may not be as bad as we think. “Bees in intensely developed land are doing just as well as those in suburbia,” Reeher said in an interview.

The study noted that, despite the difference in urbanization between the various sites, bumblebee abundance didn’t change in a substantial way at all. 

The deciding factor in how abundant pollinators would be? Floral abundance, which didn’t correlate to the amount of developed land either.

“By having a little bit of nature out there, you can get a lot of benefits,” said Randy Mitchel, co-author of the study and professor of biology at the University of Akron. “The more we’re willing to let nature have a chance, the more likely that these important critters come back near our cities.” 

How do we make space for nature in our cities?

Spaces for pollinators can be a hard sell in cities. Where a native species garden or urban farm is built could have been the prime location for a soccer field or a community center. 

But the information in this study could be vital to finding smaller, but important ways for shrinking cities like Cleveland and Youngstown to provide for their insect friends. Simple actions, such as the introduction of small, maintained spaces (named ‘micro-meadows’ in the study) could be a boon to pollinators, which in turn could travel to larger maintained areas within the city, such as urban farms and parks. Cities could even see a financial incentive to keep weedy margins around and not need to pay for a landscaper to trim them down every week.

Ecologists believe these to not only be conservationist measures, but humanitarian ones as well.

“They’re very important for urban crops, especially for people who are food insecure and require those urban crops,” professor of ecology Frances Sivakoff said. Sivakoff has been looking at pollinator interactions in urban spaces for the last five years.

55% of the world’s population lives in urban areas, according to the Food and Agriculture Organization of the UN, and 80% of food produced is destined for the city. In a search for a sustainable food system for urban dwellers, especially during current times of stress and uncertainty, it’s vital to look out for the little guy.

The little guy in this case being an inch-long bumblebee.