For 8 years, scientists studied 8 wild bumblebee species in Colorado; tongue length shaped pollen preferences, while bees shifted their diets with the seasons

An eight-year study across the Colorado Rockies has revealed that wild bumblebees are far more selective in their diets than previously thought. Bumblebees are making their own "healthy eating plans" by monitoring the levels of proteins, fats, and carbohydrates they consume throughout the season. This study, conducted by Northwestern University and the Chicago Botanic Garden, means we will never see those lovely bees in the same light again.

Bees and the best plants to eat

Researchers studied eight species of wild bumblebees visiting one field site in Colorado over eight years. They noted which flowers each species visited and took samples of pollen to analyse how much protein, fat and carbohydrates were in each sample. This gave them a database of 35 different plant species.


According to the study, larger-bodied bees with longer tongues preferred pollen that was high in protein but lower in sugars and fats, while shorter-tongued bees tended to gather pollen that was richer in carbohydrates and fats, not simply “higher in fat” as a blanket preference. This split the species into two separate “nutrient niches,” essentially, different bees eating different diets with little overlap.

Individual bees also shift their preferences through the season. In spring, queen bees seek out protein-rich pollen to provide energy for their first brood. Later in summer, as worker bees take over foraging, about half of the species shifted toward pollen with less protein and more fat, the source does not describe a shift toward higher sugar as well.

Why your garden might be a bee’s grocery store

The amount of protein in the flowers was far greater than they were expecting. Some flowers had as little as 17% protein, and others had 86% protein. This means that the difference between a protein shake and a sugary snack could be just a few feet away.

Wild bees pollinate roughly 85% of the world’s flowering plants, and three-quarters of food crops rely on insect pollinators. According to the U.S. Geological Survey, pollinators such as the western bumblebee save the U.S. agricultural industry an estimated $1.5 billion annually. Meanwhile, according to the Xerces Society, more than a quarter of native bumblebee species in North America are now at risk of extinction.

The grim reality

A study led by the USGS in 2023 looked at how western bumblebees have declined by 57% in the American West between 1998 and 2020. Increasing temperatures, drought, and the use of neonicotinoid pesticides were the main causes. If conditions get worse, the researchers predict up to 97% of these bees will decline by the 2050s.

When looking at both studies together, it shows that simply planting ‘pollinator-friendly’ flowers won’t cut it. If whole regions are losing certain flowers that provide high protein pollen in spring and high fat pollen in late summer, bees will struggle to gain the right macronutrients.

A simple solution

None of this requires new legislation. Gardeners, city planners and anyone with a window box can take away a simple lesson: a variety of nutrients, not just a variety of flowers, is what keeps bee populations fed through the year. A backyard planted with a single showy flower species may look appealing, but a mix of high-protein blooms in early spring and high-fat, high-carb blooms in late summer does more to support the bees in the neighborhood. Bumblebees have been managing their own nutrition for thousands of years, the task for us is simply not to narrow their options.