The Beekeeper’s Companion Since 1861
icon of list


Legacy of Robbin Thorp: Franklin’s Bumble Bee Proposed as Endangered Species

- October 1, 2019 -

DAVIS–The late Robbin Thorp, distinguished emeritus professor of entomology at the University of California, Davis,  and a global authority on bees, worked tirelessly to try to include Franklin’s bumble bee (Bombus franklini) as an endangered species under the U.S. Endangered Species Act (ESA).

In fact, he and the Xerces Society for Invertebrate Conservation petitioned the U.S. Fish and Wildlife Service on June 23, 2010 to include the bumble bee on the proposed list.

Today (Aug. 14) the U.S. Fish and Wildlife Service proposed that it be listed as an endangered species. If approved, Franklin’s bumble bee would be the first bee in the western United States to be officially recognized under the ESA.

Its range, a 13,300-square-mile area confined to Siskiyou and Trinity counties in California; and Jackson, Douglas and Josephine counties in Oregon, is thought to be the smallest range of any other bumble bee in the world.

Thorp, who died at age 85 on June 7 at his home in Davis, had monitored the population closely since 1998, but last saw the bumble bee in August 2006. It was he who sounded the alarm.

Thorp’s surveys clearly show the declining population. Sightings decreased from 94 in 1998 to 20 in 1999 to 9 in 2000 to one in 2001. Sightings increased slightly to 20 in 2002, but dropped to three in 2003. Thorp saw none in 2004 and 2005; one in 2006; and none since.

He refused to believe that it may be extinct. “I am still hopeful that Franklin’s bumble bee is still out there somewhere,” he said late last year.

Xerces says that the primary threats to this species are three-fold:


  1. diseases from managed bees
  2. pesticides, and
  3. a small population size


The International Union for Conservation of Nature (IUCN), the world’s oldest and largest global environmental network, named Franklin’s bumble bee “Species of the Day” on Oct. 21, 2010. IUCN placed it on the “Red List of Threatened Species” and classified it as “critically endangered” and in “imminent danger of extinction.”

Franklin’s bumble bee, mostly black, has distinctive yellow markings on the front of its thorax and top of its head. It has a solid black abdomen with just a touch of white at the tip, and an inverted U-shaped design between its wing bases.

“This bumble bee is partly at risk because of its very small range of distribution,” Thorp related recently. “Adverse effects within this narrow range can have a much greater effect on it than on more widespread bumble bees.”

If it’s given protective status, this could “stimulate research into the probable causes of its decline,” said Thorp, an active member of the Xerces Society. “This may not only lead to its recovery, but also help us better understand environmental threats to pollinators and how to prevent them in future. This petition also serves as a wake-up call to the importance of pollinators and the need to provide protections from the various threats to the health of their populations.”

Thorp hypothesized that the decline of the subgenus Bombus (including B. franklini and its closely related B. occidentalis, and two eastern species B. affinis and B. terricola) is linked to an exotic disease (or diseases) associated with the trafficking of commercially produced bumble bees for pollination of greenhouse tomatoes. Other threats may include pesticides, climate change and competition with nonnative bees.

Named in 1921 for Henry J. Franklin, who monographed the bumble bees of North and South America in 1912-13, Franklin’s bumble bee frequents California poppies, lupines, vetch, wild roses, blackberries, clover, sweet peas, horsemint and mountain penny royal during its flight season, from mid-May through September. It collects pollen primarily from lupines and poppies and gathers nectar mainly from mints. According to a Xerces Society press release, bumble bees are …