Being a single mother of 20 is no joke, especially if the survival of a whole species depends on it.
A queen bumblebee faces this very challenge when she lays her first eggs in the spring: She is utterly alone, with no worker bees to help.
She flies miles each day, collecting nectar to feed her young. She builds a protective nursery from wax. When she’s not out foraging, she climbs atop her larvae and buzzes to warm them.
“It’s extremely high stakes for the queen,” said Melanie Kimball, a postdoctoral researcher in the Department of Neurobiology, Physiology and Behavior at the University of California, Davis. “If she fails, the entire colony fails.”
After several weeks, the first workers bees finally emerge and start to help her. But even then, she will always be the single mother of her colony.
Kimball and Felicity Muth, assistant professor of neurobiology, physiology and behavior, are studying how queen bumblebees manage the challenges of starting a colony.
“They have to be good learners,” Kimball said.
In a paper published May 13 in Proceedings of the Royal Society B, Kimball and Muth report that queen bumblebees really are faster learners, able to memorize flower scents more quickly than worker bumblebees.
Their work could shed light on how cognition first evolved. It could also help scientists preserve a critical ecological link.
Bumblebees are important pollinators of native plants, and they’re crucial for crops like tomatoes, potatoes, eggplants, squash, blueberries and cranberries, which require very large pollinating insects. But North America’s native bumblebees are threatened by pesticides, habitat destruction and non-native species.
A sole survivor starts a new colony
It’s easy to imagine that all bees are purely colonial creatures, always supported by a team, the way honeybees are. But bumblebees face a more tenuous existence — because their colonies live for only a single season.
A handful of new queens emerge in the fall, near the end of the colony’s life. After spending a couple of weeks foraging for her colony, each new queen sets off alone, to mate with a male bee and dig a burrow.
As a new queen sleeps in solitude beneath the winter snow, her birth colony has long since perished. These solo queens, hunkering alone in the darkness, are their colony’s only surviving link to the future.
For each queen that survives the winter and emerges the following summer, there is urgent business. She must forage and replenish her calories, find a place to nest, build chambers of wax, and gather a store of honey. Only then can she start raising her first batch of workers.
“The queen has to survive so many stages just to start reproducing,” said Kimball. “She is doing all of this alone.”
Although people have studied the cognitive prowess of worker bumblebees for years, Muth wondered whether — because of the many challenges they face — queen bees might actually be smarter than workers. So, several years ago, she started visiting meadows in the Sierra Nevada during the brief early summer window when new queens can still be found foraging.
She netted them one by one, put each one in a chamber, and tested how quickly it learned to associate certain colors with rewards like sugar water.
“The queens learned much more quickly than the workers,” said Muth. She published these results in Biology Letters in 2021.
This suggested that queens might be smarter than workers. But it couldn’t rule out other explanations — for example, that queens might just have keener eyesight or be better visual learners. When Kimball joined Muth’s lab in 2024, she set out to test whether queens also excel at other types of learning.
Threatened pollinators and the origins of thought
Working with captive bumblebees, Kimball tested how readily the queens and workers learned to associate scents with rewards. Combining this with experiments that Muth had done in the Sierra, she found that queens are also faster olfactory learners.
“This suggests that the bumblebee queens may be faster learners in a general way,” said Kimball. She also found that queens can identify scents at lower concentrations than workers. “Outside in a meadow, this may help them differentiate and find the best flowers more quickly.”
Muth and Kimball believe that by comparing queens and workers of the same species, they can eventually isolate the differences in brain structure and chemistry that enable faster learning.
In the long run, they hope to learn how cognition evolved on Earth.
“It’s really interesting that cognitive abilities exist across such a broad range of animals, from mammals to insects to octopuses,” said Kimball. Studying these vastly different minds could reveal the fundamental underpinnings of learning, reasoning and thought.
Understanding how bumblebees learn could also help biologists protect a vital ecological service. North America’s forests, prairies and other landscapes evolved to depend heavily on bumblebees for pollination.
Even today, farmers still have to rely on bumblebees to pollinate crops like squash and tomatoes that require the intense buzzing and vibration of a very big insect to release their pollen.
But California’s bumblebees are increasingly threatened by habitat loss and competition from non-native honeybees, which were introduced by European settlers centuries ago. Bumblebees are also harmed by some insecticides, which Muth has found can actually blunt their ability to learn flower scents.
“Bumblebees have been living alongside our native plants in North America for a long time,” said Kimball. “They’re really important.”
Muth and Kimball’s research on bumblebee learning is supported by a grant from the National Geographic Society and the Templeton World Charity Foundation, as part of the Wildlife Intelligence Project.
Media Resources
Bumblebee queens are better at olfactory learning and more sensitive to scents than workers (Proc. Roy. Soc. B)
