A bumblebee’s brain is smaller than a sesame seed. But it can still accomplish quite a bit.

“You don’t need a big brain to learn well,” said Felicity Muth, an assistant professor in the Department of Neurobiology, Physiology and Behavior and a National Geographic Explorer who studies cognition in bees and other animals. “Bumblebees are capable of many of the same cognitive feats as many vertebrates.”

Previously, Muth studied the behavior of birds. But now she studies the thought processes of bumblebees — how they learn, how they choose which flowers to visit — and what motivates them. Her goal, said Muth, is to understand how they think about the world that they inhabit.

Caffeinated creepy crawlies

Muth studies the dynamics of reward and manipulation that play out between bumblebees and the plants that they visit. It is well known that plants reward bees with sugar-rich nectar to motivate the bee to visit more of the same type of flower — carrying pollen between the plants, and thereby helping them reproduce.

But many plants also have tricks for grabbing the bees’ attention, getting them to remember and return, and supercharging their frenetic flower-visiting, all while minimizing the amount of sugar they have to produce and give away. The nectars of many flower species contain caffeine. These same nectars also often contain octopamine and tyramin, chemicals that function as hormones and neurotransmitters in the brains of insects.

Muth has studied these interactions in the lab, where she can fill artificial flowers with carefully mixed cocktails of nectar and plant chemicals, and measure how they affect the bees. 

“The plants are actually manipulating the insects,” said Muth.

She has found that when bumblebees drink nectar containing caffeine, they respond as if it contains more sugar than it actually does. The spike of caffeine makes them more likely to remember those flowers and visit them again another day. 

The caffeine also causes them to flit around more frenetically, visiting more flowers per second. However, this is not the whole story. If the flower nectar also contains octopamine and tyramine, this erases the effect of caffeine. Real nectar, of course, contains hundreds of chemicals and Muth’s work is shedding light on their complex, interacting effects.

The challenges of bee-ing

In addition to their time in the lab, Muth and her students spend much of the summer outside, traveling from one alpine meadow to another in California’s Sierra Nevada.

There, they catch wild-foraging bumblebees in nets. They transfer each insect to its own container (a clear plastic cylinder) and test its ability to learn and remember.

They do this by sliding tabs of colored paper into narrow slits in the plastic tube. Some of those papers are soaked in sugar water; others are soaked in water alone. The curious insect discovers this as it reaches out its tongue-like proboscis for a taste: taking a good long sip if it’s sugar water, or recoiling instinctively if it’s water, which tastes bad to bees.

In 2021, Muth and her former postdoc mentor, Anne Leonard of the University of Nevada, Reno published a study in which they used this setup to test the bumblebees’ ability to associate particular colors with food. They found that female worker bees and male drone bees each learned equally well, though the males were slower to make decisions. But the more interesting insight came later from the other, larger bees they tested.

They had visited the meadow early enough in the spring that queen bumblebees, which hibernate through the winter, had emerged to spend a couple of weeks foraging before retreating permanently into a burrow and starting a colony. 

“Queens are much more elusive than workers. They are much less studied, and that’s what drew me to them,” said Muth. 

Compared to workers, queens have only a short time to forage, because colonies need to be started early in the season to have the best chance of success. 

“They have to move quickly,” said Muth. “They’ve got to be smart. There’s so much pressure on them at this stage.”

Muth found that queens captured in the wild were significantly faster learners than female workers of the same species.

From bees to birds (and bipeds)

In the summer of 2024, Muth was back in the meadows again, catching workers and queens. This time, rather than colors, she tested the bumblebees’ ability to associate certain odors with food. Those results are still preliminary, but at first glance, the queens once again seemed to learn more quickly than the workers.

Over time, Muth hopes to understand the queen bumblebees’ learning abilities with more nuance. She believes that their brainpower is shaped by the specific challenges that they face, which workers don’t encounter: not just foraging, but also finding and choosing mates and selecting nesting sites. 

“They probably have cognitive specialization that goes beyond just being a bigger bee with a bigger brain,” she said.

Her eventual goal is to understand how the obstacles faced by animals shape their specific cognitive traits. It’s a question that goes well beyond insects. It could shed light on how intelligence evolved in other, distantly related animals, including birds, mammals and even humans. If we can understand this, she said, it will help us understand ourselves better.

Muth’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.