Early morning sunlight and strong cooling winds hit the roof of a 52-story Chicago high-rise, where three wooden structures that, in another setting, might look like unfinished filing cabinets sit in a row. They are tucked up against an overhang that buffers them from lake breezes in the winter. But inside of these structures, you won’t find files. Instead, they hold tens of thousands of honey bees, whose honey serves as a perk for the building’s tenants. The bees drink from the rooftop garden water lines, and the golden-yellow flowers of sedum plants are a convenient source of pollen and nectar. Flowers in parkways and median planters, weeds in abandoned lots, and plants in other rooftop gardens also attract the foraging bees. “The city is their garden,” says Sarah Long, the lead beekeeper.
Long works for Best Bees Company, which provides beekeeping services to clients across the country who want to start honey bee programs. They also collect data on their hives and the honey the bees produce, with the aim of contributing to the overall movement to “save the bees.” Each hive they maintain represents a data point that supports research on improving pollinator health. Long believes in the benefits of rooftop programs. “Studies have shown that urban settings have more plant diversity than rural settings,” Long says. “Just like humans, more diverse diets are thought to provide better nutrition and be better for bee health.”
While it may seem strange that these insects live more than 50 stories up in the middle of the Windy City, Corky Schnadt, president of the Illinois State Beekeepers Association, notes that a Chicago rooftop is a surprisingly good habitat for beekeeping. “Honey bees travel up to three-and-a-half miles to find forage, so an elevation of 695 feet doesn’t add too much to the distance,” says Schnadt. “Chicago, at least historically, uses less pesticides, and there is a lot more greenery than you would imagine in the city’s parkways.”
In addition to some famous hives like the ones atop the White House and the Colorado Convention Center, more than 2.98 million honey bee colonies are registered across the US, according to the US Department of Agriculture. In 2019, 4,922 beekeepers registered more than 6,000 apiaries with 34,255 active honey bee colonies in Illinois, according to the state’s own agriculture department. State-specific statistics probably reflect low-end estimates, as hive registration is not required in many states, and backyard or urban beekeepers with fewer than five hives are not counted nationally.
But the growing interest in hobbyist beekeeping has some ecologists worried. The European honey bee, as its name might suggest, is not native to North America and was brought over in the 17th century for agricultural and economic purposes. While honey bees are a managed pollinator species, about 4,000 species of native bees also call the US home, including its urban areas. One group of researchers observed dozens of wild species across several Chicago neighborhoods, while another nature organization recorded more than 200 species in New York City. Now, some ecologists are concerned that with so much human help, the newcomers might outcompete their wild cousins, causing an ecological ripple effect that would threaten both the bees and the plants that depend on them.
In August, Monika Egerer, a postdoctoral fellow at the Technical University of Berlin, published a paper in the journal Trends in Ecology & Evolution about the “Gordian Knot” of urban beekeeping, borrowing a metaphor from Greek mythology representing a problem with little or no solution. “Urban beekeeping is a tricky, complex problem tied up like a knot, and many people want a simple way to untie it,” says Egerer, who will be heading to the Department of Ecology and Ecosystem Management at the Technical University of Munich this October. “But there’s no one way to solve this issue, and it really is city context dependent.”
One of the main problems comes down to competition for food. In one analysis of rooftop bees’ honey, Best Bees found up to 181 different kinds of plant DNA, suggesting they have a generalist diet, including many kinds of flowering plants. But some native bees are a bit pickier. For example, squash and sunflower bees specialize in their respective namesakes. Disrupting this delicate, symbiotic relationship by adding a host of managed honey bees to an area can threaten the survival of specialist bees.
A 2019 study conducted in Paris found that wild bee foraging was negatively associated with honey bee population density. An earlier one in Melbourne, Australia, found that bee species diversity was higher in areas with fewer honey bees. In addition to competition for floral resources, the health and reproductive success of wild bees is also at risk in areas with an abundance of honey bees. Honey bees can spread pathogens, which have the potential to decimate species, Egerer says. A 2017 study in California showed that wild bee parasite loads were higher in urban gardens with lots of honey bees.
Furthermore, a decrease in wild bees may have a detrimental effect on native plants, which lose needed pollination. “If wild bees leave the habitat because there is some sort of antagonistic interaction, either direct or indirect, then we may lose the pollination services of wild plant species,” Egerer says. “This may have a big impact on the structuring and functioning of an entire ecosystem.”
But this doesn’t mean the public should forget about honey bees, who also face their own threats. Colony collapse disorder (CCD) is a hive phenomenon in which the majority of worker bees die, leaving the queen behind with a few nurse bees. Pesticides and poor nutrition probably play a role in CCD, but the parasitic Varroa mite appears to be the main culprit, as it feeds on fat stores in adult and larval honey bees and spreads viruses, one of which is deadly. During the first quarter of this year, the USDA reported that the number of colonies in operations containing five or more hives that exhibited CCD symptoms was up 76 percent over the same period last year. But, the agency also reported, the number of colonies in the US is growing: 2.88 million, an increase of 8 percent compared to the year before.
Adam Dolezal, an entomologist who studies honey bees at the University of Illinois, says that while urban beekeeping ventures increase awareness about the risks the insects are facing, they do not fix the core problems. “Honey bee losses are driven by a complex network of interactions between pathogens, pesticide exposure, and a reduction in floral resources in the landscape,” Dolezal says. “And do I think keeping bees on rooftops in large cities addresses these issues? I don’t think so.”
However, Dolezal acknowledges that work done by Best Bees and academics helps maintain healthy populations for all kinds of bees. For example, Best Bees collects data that benefits scientific research, and Long checks her bees regularly for mites to prevent the spread of disease. “Some may argue we shouldn’t keep honey bees at all because it introduces competition for native bees,” Dolezal says. “But I don't think these two things have to be at odds with one another."
Long agrees. “I think the effect of honey bees on native bee species is a worthy concern,” she says. “But we assume that actions that protect honey bees, like using fewer pesticides and planting pollinator-friendly areas, would benefit native insects as well.”
“In theory,” she continues, “more pollinator activity should increase pollination, fruit-set, seeds, and therefore result in more plants.”
Bee experts also agree that offering city dwellers an opportunity to observe a slice of the natural world has its own benefits, especially if it raises awareness about struggling bee populations. “All of a sudden, people become more aware and start planting more flowers in their gardens or on their balconies,” Schnadt says. “Or maybe they’re not so quick to kill the dandelions in their gardens, which are a major source for pollen and nectar in the early spring.”
Egerer believes there are many threads tangled in this story of overlapping conservation efforts and that there’s no one-size-fits-all solution. In her paper, she suggests that one way to begin untangling the knot is city-mandated honey bee colony registration. Perhaps cities could limit the number of hives in one area, which would reduce competition for food between species and limit the spread of pathogens. Unlike honey bees, many native species are solitary and nest in the ground, so another stewardship solution might be providing adequate nesting habitat for them, like sandy ground, dead wood, and native flowers.
“Thinking about beekeeping in an urban context is a great entry point into thinking about how we are stewards of our environment and whether we can implement different environmental strategies to support all types of biodiversity,” Egerer says. “Having that recognition is a great first step, and then we can talk about how to mitigate potential impacts of urban beekeeping.”