April 8 Chapter Meeting

Title of Talk: California Bumble Bees and Their Use of Native Plants

April 8, 2026 at 7:00 PM

The meeting will be held at Shepard Garden & Arts Center, 3330 McKinley Blvd. , Sacramento.  This will be a “hybrid” meeting and will be streamed on Zoom. Click here to register and attend via Zoom.

Summary

California is home to more than 1,600 species of native bees, the conservation needs of many of them unclear. Conservation efforts for at-risk species are limited by a lack of rigorously collected occurrence data, even for species in the best-known groups, such as bumble bees (Bombus).

The California Bumble Bee Atlas, a project of the Xerces Society for Invertebrate Conservation and partners, is a community science effort to document the distribution of the state’s native bumble bees, their habitats, and host plant associations. Active since 2022, the project has trained more than 1,900 community scientists, who together have recorded nearly 25,000 individual bee observations during ~2,300 standardized field surveys across the state.

We have documented 23 species of bumble bees foraging at nearly 500 genera of native and introduced plants, representing thousands of plant species. Bumble bees are considered host plant generalists, yet plant use patterns varied greatly among bee species and castes, highlighting the need to plan restoration actions around focal species’ diets. Our study shows that California native plants are critical to the diet of these bees, and also that they are pollinators of some of the state’s rarest plants. Given imperilment of nearly ¼ of bumble bee species, driven by habitat loss, pesticide exposure, and climate change, we contend that effective conservation of the state’s native plants must consider the plight of these important plant mutualists.

Speaker Bio

Dr. Richardson is a conservation biologist with The Xerces Society for Invertebrate Conservation, where he leads the California Bumble Bee Atlas, a community science project to inventory the native bees of the state. More generally, his research focuses on the ecology, distribution, and declines of North American bumble bees. Dr. Richardson previously worked as an environmental consultant, studying pesticide risk to bee pollinators, and as an ecologist for Vermont Fish and Wildlife Department. He is co-author of a range of scientific publications on bees, including Bumble Bees of North America: An Identification Guide (2014), a standard reference manual on this group of insects. He is an expert in the inventory and identification of bumble bees, and has extensive experience training others to collect bumble bee distribution data in the field.

Photos courtesy of Dr. Richardson.