Forget the idea of bees randomly winging it from flower to flower. These fuzzy foragers aren’t just buzzing around — they’re on a mission. Recent research reveals that wild bumblebees adjust their diets to meet specific nutritional needs for protein, fat, and carbohydrates, making them nature’s original macro-trackers.

In the first long-term study of bumblebee nutrition in the wild, a team of ecologists tracked eight species of bumblebees over a period of eight years at a field site in the Rocky Mountains, Colorado, USA.

The researchers closely monitored which flowers each bee species visited for pollen. They then collected samples of the pollen to study its nutrient content, working out the concentrations of protein, fat, and carbohydrates across 35 different plant species.

Protein made up only 17 percent of the pollen in some flowers, but in others it reached as high as 86 percent.

“All pollen contains protein, fats, and carbs,” said Justin Bain, the study’s first author. “But each type of pollen has a different mixture of these macronutrients. Some are very high in protein, like a steak. Others are more like a salad. So, the nutritional profiles are very, very different.”

The researchers then compared the diet of each bee species with their physical traits, such as tongue length, and with seasonal changes in flower availability. They noticed clear patterns.

They found that the eight bee species fell into two distinct groups. Bees with bigger bodies and longer tongues favoured protein-rich pollen that was lower in fats and sugars. Shorter-tongued bees preferred pollen higher in fats and carbohydrates and lower in protein. These differences likely relate to tongue length influencing which flowers each species can access — and help them avoid direct competition despite sharing the same habitat.

Major seasonal changes were also observed in pollen’s nutrient content. Spring flowers tended to be higher in protein, while late summer blooms were higher in fats and carbohydrates. This shift in nutritional composition aligned closely with the changing dietary preferences of bees throughout the season.

“Queen bees emerge in the spring to establish their colonies,” Bain said. “They forage when the snow first melts, collecting protein-rich pollen for themselves and their first brood. Later in the summer, worker bees take over foraging, and half of the species shifted toward pollen with less protein and more fats. Seeing these clear transitions between queens and workers was especially striking, and it highlighted how differently species meet their nutritional needs across the colony life cycle.”

Wild bumblebees primarily consume two types of food from flowers: nectar, which is sweet and syrupy, and pollen, which is rich in fats and proteins. Adult bees get short bursts of energy from sipping nectar. They also gather pollen to feed their brood and support growth. Worker bees collect pollen from a variety of flowers, carrying it home to their young in special “baskets” on their hind legs.

This research doesn’t just help us understand bee behaviour, it gives us a clear path to help them thrive.

Bees and other pollinators face serious challenges, from pesticides and habitat loss to poor nutrition and climate change. These findings could help gardeners and conservationists create spaces that truly support bees. This isn’t just about planting more flowers — it’s about planting the right mix. By choosing plants that provide a variety of macronutrients throughout the seasons, we can help bees meet their changing dietary needs.

Whether you’re planting a backyard garden or restoring a meadow, consider including a variety of native plants that bloom at different times and keep bees well-fed with a changing menu of pollen. This simple shift could have a big ecological impact.

“Despite the general importance of wild pollinators, especially bees, we know very little about their nutritional needs,” said the study’s senior author, Northwestern University’s Paul CaraDonna. “Given widespread pollinator declines that have been observed around the globe, this knowledge gap is surprising and concerning. Our research provides some of the best information yet on the availability of nutritional resources found in wildflowers and how pollinators use these resources. We can incorporate this work into our thinking about garden design, so we can select the right flowers that best support the nutritional needs of wild pollinators.”

CaraDonna is an expert on plant–pollinator interactions and an adjunct associate professor in the Program in Plant Biology and Conservation, a partnership between Northwestern’s Weinberg College of Arts and Sciences and the Chicago Botanic Garden.

Justin Bain is a recent Ph.D. graduate from CaraDonna’s lab group. This study was part of his dissertation and was published on 26 August 2025 in the Proceedings of the Royal Society B: Biological Sciences.