Mysterious red honey began to appear in the hives of New York City bees in the summer of 2010. At first, beekeepers thought their bees were foraging on some strange plant, possibly sumac. But after more beekeepers began to find red honey in their hives, they decided to get their honey tested. As it turned out, the honey was filled with Red Dye No. 40, and instead of foraging on flowers, the bees had been collecting sugar syrup from a Maraschino cherry factory in Brooklyn.
The story of New York’s red honey struck a chord with those already concerned about honey bee health. Bees have been hit hard by a host of challenges ranging from parasitic mites to neonicotenoid pesticides—but could red honey be another sign of bee decline? Could artificial flavors and chemicals in human foods be toxic to bees? Could we be at risk if we eat “local honey”?
As people were asking questions about New York’s bees, my lab group was studying another insect in New York—ants. Over 8.9 million people live in New York, but there are at least 16 billion ants. That means for each person living in New York there are nearly 2,000 ants. In an area that is almost 90% concrete, how could so many ants survive? The secret, we thought, might lie in what was happening with New York’s bees. Rather than feeding on dead insects and other “natural” foods, we guessed ants might be switching to human foods.
The average person living in a city produces 1,000 pounds of garbage each year, and of that, 15% is food waste. With over half the world’s population now living in cities, this amounts to 250 million tons of food thrown out in cities each year, which represents a massive potential resource for urban animals. We found that much of this food in New York was making it into urban ant colonies. This was especially true in the most urban areas of the city, like the sidewalks running down Broadway. A follow-up study found that ants living on Broadway alone consumed the equivalent of 60,000 hotdogs per year—more than city rats or birds consumed in the same area.
But what about urban bees? Anecdotes about red honey aside, no serious investigation had been carried out on the diet of urban bees. Over the last decade, cities began to change local ordinances that had previously outlawed beekeeping inside city limits, and urban beekeeping has become increasingly popular. Along with backyard chickens and rooftop gardens, urban beekeeping has become a major part of the local food movement. In fact, the red honey discovered in New York was intended for a local restaurant until it turned out to be recycled sugar syrup. Despite growing interests in urban bees, there was still no clear answer as to whether bees were sticking to flower nectar or finding new sugar sources in cities.
Using the same techniques we used to study ants in New York, we began studying the diet of bees in Raleigh, North Carolina. Human-produced sugars, like sugarcane and high-fructose corn syrup, have a characteristic carbon isotope signature that can be used to determine if bees are feeding on flower nectar or, say, someone’s leftover soda. Bees in rural areas should only have access to flower nectar, but if city bees are feeding on human food sources, then their carbon isotope signature should show it.
To our surprise, we found no difference in carbon isotopes between bees living in downtown Raleigh and those living outside the city. In both habitats, bees were sticking to flower nectar and largely avoiding human sugar sources. This is good news for urban beekeepers and people who buy local honey, and it also shows that urban flowers play a major role in maintaining healthy pollinator populations in cities.
In the future, we plan to partner with urban beekeepers in larger cities, like New York and Tokyo, to see if bees are still able to sustain their colonies on local flowers. Will we find bees similar to those in Raleigh, or will we uncover new mysterious shades of honey inside the hives of big-city bees?
Featured image credit: “Bee foraging on flowers outside lab at NC State” by Lauren Nichols. Used with permission.