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U.S. Forest Service

Franklin's Bumble Bee (Bombus franklini)

By Evan Cole, Pollinator Partnership

Only found across northern California and southern Oregon between the Coast and Sierra-Cascade mountain ranges, Franklin’s bumble bee holds the distinction of having the narrowest distribution of any bumble bee in the world. The rare and endemic nature of Franklin’s bumble bee adds to the fragility of the species, and makes the recent population decline even more alarming. Until 1998, Franklin’s bumble bee was highly prevalent throughout its range. Recent surveys since 2004 have been almost entirely incapable of observing a single specimen. The species is currently listed as a “species of concern” by the US Fish and Wildlife Service, which means that there are no conservation measures in place to protect the species until further information is collected. In 2009, the International Union for Conservation of Nature (IUCN) Red List of endangered species listed Franklin’s bumble bee as “imperiled” and stated that the species’ population has likely dropped to dangerously low levels. It is of critical importance that a proper scientific investigation is pursued in order to determine the actual status of Franklin’s bumble bee. If its population has indeed reached a critical level, the species will require extensive protection in order to avoid extinction.

Franklin’s bumble bee is easily identified by the extended yellow on the anterior top of the thorax that extends behind the wing bases and forms an upside-down U-shape around the central patch of black. There is no yellow on the abdomen, which has white at its tip, and the face is mostly black.

Bombus franklini Franklin’s bumble bee, Bombus Franklini. Photo by James P. Strange, USDA-ARS Pollinating Insect Research Unit.

Franklin’s bumble bee is easily identified by the extended yellow on the anterior top of the thorax that extends behind the wing bases and forms an upside-down U-shape around the central patch of black. There is no yellow on the abdomen, which has white at its tip, and the face is mostly black.

Franklin’s bumble bee relies upon floral plants, such as Lupinus, Eschscholzia, Agastache, Monardella, and Vicia, and abandoned rodent burrows for its habitat. Bumble bees are social creatures and live in busy colonies. They pollinate plants by vibrating the pollen loose from the flower anthers, producing their signature buzzing sound. This unique method of pollination is essential to the production of tomatoes, blueberries, and many other popular plants.

Colonies are established annually by solitary mated queens, which take on the duty of collecting nectar and pollen to support the production of eggs that were fertilized the previous fall. The offspring then take over the role of defending the colony and collecting food. Near the end of the cycle, new queens are produced, which then mate with males and build their fat reserves in order to hibernate through the winter. The founding queen, along with all of the workers, dies at the end of the colony season, leaving only the new queens to establish new colonies the following year.

Bombus franklini Bombus franklini. Illustration courtesy of Elaine Evans, Xerces Society

There are currently a number of threats to the health and survival of Franklin’s bumble bee. The use of commercial bumble bee colonies to pollinate crops has transmitted a variety of diseases and genetic disorders to native populations. Also, the expansion of agriculture throughout the species’ native range has caused extensive habitat degradation and destruction. Improper and excessive application of pesticides to crops, gardens, and lawns can poison bees, especially ground-dwelling colonies of Franklin’s bumble bee. Non-native and invasive plants that have been introduced to northern California and southern Oregon can outcompete the plants that Franklin’s bumble bee relies upon for food.

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