Project Bumble Bee

In the late 1990’s, bee biologists started to notice a decline in the abundance and distribution of several wild bumble bee species. Five of these species (western bumble bee, rusty patched bumble bee, yellowbanded bumble bee and the American bumble bee) were once very common and important crop pollinators over their ranges. Franklin’s bumble bee was historically found only in a small area in southern Oregon and northern California, and it may now be extinct. We’ve recently launched a collaborative citizen science project called Bumble Bee Watch to track these and all other North American bumble bees.

Recent research indicates that additional species of bumble bees may be in decline. Wild bumble bees face many threats including habitat alteration, pesticide use, management practices, and pathogens. Recent reports are troubling, but there is much you can do to help!

To read more about recent declines see the Threats section below.

Recent efforts to track the western bumble bee

This project was funded by the Oregon Zoo.

What you can do!

Create habitat!

Download our new publication:  Conserving Bumble Bees. Guidelines for Creating and Managing Habitat for America’s Declining Pollinators.  

The Xerces Society has collaborated with the Lady Bird Johnson Wildflower Center to create a list of plants that are attractive to bumble bees, please consider using this valuable resource.

Participate in our citizen science project:

We are very interested in tracking all species of North American bumble bees at our new citizen science website Bumble Bee Watch!

Below is a map of the citizen records. Citizen science has greatly helped us to understand the distribution and nesting habits of these important yet imperiled pollinators and will help us to target our conservation efforts.


Have you seen an active bumble bee nest?

We are collecting data on bumble bee nesting habits.  Please visit to submit a nest sighting.


There are a number of threats facing bumble bees, any of which may be leading to the decline of these species. The major threats to bumble bees include: spread of pests and diseases through commercial bumble bee rearing or other methods, habitat destruction or alteration, pesticides, invasive species, low genetic diversity and climate change.

Commercial bumble bee rearing may be the greatest threat to B. affinis, B. occidentalis, B. terricola, and B. franklini. In North America, two bumble bee species have been commercially reared for pollination of greenhouse tomatoes and other crops: B. occidentalis and B. impatiens. Between 1992 and 1994, queens of B. occidentalis and B. impatiens were shipped to European rearing facilities, where colonies were produced then shipped back to the U.S. for commercial pollination. Bumble bee expert Robbin Thorp has hypothesized that these bumble bee colonies acquired a disease (probably a virulent strain of the microsporidian Nosema bombi) from a European bee that was in the same rearing facility, the buff-tailed bumble bee (Bombus terrestris). The North American bumble bees would have had no prior resistance to this pathogen. Dr. Thorp hypothesizes that the disease then spread to wild populations of B. occidentalis and B. franklini in the West (from exposure to infected populations of commercially reared B. occidentalis), and B. affinis and B. terricola in the East (from exposure to commercially reared B. impatiens). In the late 1990’s, biologists began to notice that B. affinis, B. occidentalis, B. terricola, and B. franklini were severely declining.

Where these bees were once very common, they were nearly impossible to find. B. impatiens has not shown a dramatic decline; Robbin Thorp hypothesizes that B. impatiens may serve as a carrier of an exotic strain of Nosema bombi, although it may not be as severly affected by the disease as B. affinis, B. occidentalis, B. terricola, and B. franklini. B. affinis, B. occidentalis, B. terricola, and B. franklini are closely related to each other (they all belong to the subgenus Bombus sensu stricto).

This hypothesis was supported by a recent study led by Sydney Cameron, Ph.D., published in the Proceedings of the National Academy of Sciences. They found that the western bumble bee and the American bumble bee had significantly higher infection rates from a fungal parasite than more stable species.  They also found that these two species had lower genetic diversity than species that were not in decline.  Research is currently underway in Dr. Cameron’s lab to determine whether or not this fungal parasite was introduced from Europe via the commercial bumble bee trade. You can read more about their study and its implications here. The Xerces Society is currently working to urge the USDA Animal and Plant Health Inspection Service to regulate the commercial bumble bee trade. You can read a status review that includes more details on this issue and the decline of three bumble bees that was written by Dr. Robbin Thorp and The Xerces Society.


All bumble bees belong to the genus Bombus within the family Apidae. The family Apidae includes the well-known honey bees and bumble bees, as well as carpenter bees, cuckoo bees, digger bees, stingless bees, and orchid bees. B. affinis, B. terricola, B. occidentalis, and B. franklini all belong to the same sub-genus of Bombus, Bombus sensu stricto.

Bumble bees are important pollinators of wild flowering plants and crops. As generalist foragers, they do not depend on any one flower type. However, some plants do rely on bumble bees to achieve pollination. Loss of bumble bees can have far ranging ecological impacts due to their role as pollinators. In Britain and the Netherlands, where multiple bumble bee and other bee species have gone extinct, there is evidence of decline in the abundances of insect pollinated plants. Bumble bees are also excellent pollinators of many crops. Bumble bees are able to fly in cooler temperatures and lower light levels than many other bees, and they perform a behavior called “buzz pollination,” in which the bee grabs the pollen producing structure of the flower in her jaws and vibrates her wing musculature causing vibrations that dislodge pollen that would have otherwise remained trapped in the flower’s anthers. Some plants, including tomatoes, peppers, and cranberries, require buzz pollination. Read more.

Xerces Society bumble bee conservation efforts

On February 10, 2010, a broad coalition of scientists submitted a letter to the USDA’s Animal and Plant Health Inspection Service (APHIS) requesting that they create new regulations to protect wild bumble bees from threats posed by commercial bumble bees. The letter was signed by over 60 scientists with research on bumble bees and other bees, including: Charles D. Michener, Ph.D., author of The Bees of the World; Bernd Heinrich, Ph.D., author of Bumblebee Economics; David Goulson, Ph.D., author of Bumblebees: Their Behaviour, Ecology and Conservation, James Thomson, Ph.D., co-author of The Natural History of Bumble Bees; and May Berenbaum, Ph.D., Chair of the National Research Council Committee on the Status of Pollinators in North America. Letters of support were also submitted by native plant societies, sustainable agriculture organizations and conservation organizations.

On January 12, 2010, The Xerces Society, Defenders of Wildlife, Natural Resources Defense Council and Dr. Robbin Thorp submitted a petition to the USDA’s Animal and Plant Health Inspection Service (APHIS) requesting that they create new regulations to protect wild bumble bees from disease. In order to prevent the spread of disease to wild populations of agriculturally significant bee pollinators, petitioners asked APHIS to use its authority to regulate the movement and health of commercial bumble bees. Specifically, petitioners requested that APHIS create rules prohibiting the movement of bumble bees outside of their native ranges and regulate interstate movement of bumble bee pollinators within their native ranges by requiring permits that show that bumble bees are certified as disease-free prior to movement. Read more about this action. Read the petition.

For a brief summary of this issue, read our fact sheet.


Contributors to the bumble bee project

A number of scientists and citizen monitors have contributed their unpublished records or other information regarding bumble bees for our efforts; we greatly appreciate their collaboration:

Bernd Heinrich, Professor Emeritus, University of Vermont Chiho Kimoto and Sandy DeBano, Oregon State University, Hermiston Field Station Chris Maier, Connecticut Agricultural Experiment Station Christina North, University of Illinois David W. Inouye, University of Maryland Dale Reimer, retired Doug Golick, University of Nebraska Elaine Evans Elizabeth Elle, Simon Fraser University Howard Ginsburg, USGS Patuxent Wildlife Research Center James Strange, USDA-ARS Logan-Bee Lab Jennifer Grixti and Colin Favret, University of Illinois Jodi DeLong, freelance writer John Neff, Central Texas Melittological Institute Kevin Alexander, Western State College of Colorado Larry Stevens, Museum of Northern Arizona Lee Solter, Illinois Natural History Survey Liz Day Matthew Bowser, Kenai National Wildlife Refuge Michael Otterstatter, University of Toronto Mike Quinn Pete Schroeder, Southern Oregon University Ralph Cartar, University of Calgary Rebecca Irwin, Dartmouth College Robbin Thorp, Professor Emeritus, U.C. Davis Robert Jacobson Robert Jean and Peter Scott, Indiana State University Sheila Colla, graduate student of Laurence Packer, York University Sam Droege, USGS Patuxtent Wildlife Research Center Steve Hendrix and Chris Gienapp, University of Iowa Sydney Cameron, University of Illinois Sue Sheehan, Fermilab, Batavia, IL T’ai Roulston, Research Associate Professor, University of Virginia Leif Richardson, Dartmouth College



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