Wild Bumblebees Shift Pollen Diets With Seasons

An eight-year Colorado study shows wild bumblebees balance protein, fat, and carbohydrate intake by changing which flowers they visit.

Updated on Nov. 7, 2026 in Nutrition

Wild bumblebee with pollen-dusted legs perched on a purple wildflower in a Colorado mountain meadow with distant foothills. — Wild bumblebees in Colorado shift which flowers and pollen they gather across seasons, balancing protein, fat, and carbohydrate needs over an eight-year Northwestern and Chicago Botanic Garden study. AI Illustration. Upload story photo >

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Would you plant a mix of flowers to feed bees through the season?

Northwestern University and Chicago Botanic Garden researchers tracked eight wild bumblebee species at a Colorado field site over eight years. The study found bees adjust their pollen choices across seasons to meet nutritional needs.

Why it matters

Wild bees pollinate roughly 85% of the world's flowering plants, and the study shows their foraging depends on the nutritional mix of available pollen. Understanding these diet preferences helps explain why pollinator populations are vulnerable to habitat and climate changes.

The study monitored eight wild bumblebee species over eight years and built a nutrient database covering 35 plant species, with pollen protein content ranging from 17% to 86%. The research was conducted at a single field site, so the extent to which these patterns hold across other regions remains unaddressed.

The players

Northwestern University

A private research university in Evanston, Illinois, known for its interdisciplinary science programs.

Chicago Botanic Garden

A botanical garden and research institution in Glencoe, Illinois, active in plant and pollinator science.

The details

Researchers recorded which flowers each bumblebee species visited and sampled pollen to analyze protein, fat, and carbohydrate content. Larger-bodied, long-tongued bees preferred higher-protein, lower-sugar pollen, while shorter-tongued bees gathered pollen richer in carbohydrates and fats.

Eight-year study period conducted across eight seasons
Spring: queen bees seek protein-rich pollen for their first brood
Late summer: worker bees shift toward lower-protein, higher-fat pollen

Health Landscape

The eight-year Colorado diet study builds on the 2023 USGS-led report documenting a 57% decline in western bumblebees from 1998 to 2020. Its findings on how nutritional needs drive foraging help explain why those populations face mounting pressure from warming temperatures and pesticide use.

The findings suggest that planting a mix of flowers with varied protein and sugar content may better support local bees across seasons. Gardeners who choose diverse blooming plants can help meet the nutritional needs pollinators rely on.

The takeaway

Pollinators depend on a changing menu of flowers to meet their nutritional needs throughout the year. Planting a variety of blooming species that flower across seasons can help sustain them.