A story of Discovery & Hope

By Pepper Trail
Article and photos (unless noted)

Pepper Trail examining a captured bumble bee

Naturalist and writer Pepper Trail is a long-time supporter of the Southern Oregon Land Conservancy. His contributions to the conservation of our region's biodiversity include working on the establishment and expansion of the Cascade-Siskiyou National Monument, and searching for the endangered Franklin's Bumble Bee. Though he hasn't yet found a Franklin's, he continues to survey for other bumble bee species as a volunteer for the Pacific Northwest Bumble Bee Atlas project.

Bumble bees are the hobbits of the insect world: plump, hairy, good-natured, and industrious. How delightful it is to watch them fumble around in the flowers of thimbleberry, or spiral around the spire of a Spiraea! But behind their bumbling manner, bumble bees are vital pollinators, and among the most highly evolved of all social insects.

Franklin’s Bumble Bee. Photo by Peter Schroeder.

Sadly, like so many pollinators, bumble bees are in trouble. The Rusty-patched Bumble Bee, once common in the eastern U.S., was recently listed as Endangered under the Endangered Species Act, and several other species have declined so precipitously that they are also being considered for listing. In fact, our region is home (was home?) to the most threatened bumble bee of all – Franklin’s Bumble Bee. This species was found only from Douglas County down to Siskiyou and Trinity Counties in California – perhaps the smallest range of any bumble bee in the world. Once fairly common within that small area, Franklin’s became harder and harder to find in the 1990s. By the early years of the 21st century, Dr. Robbin Thorp, the authority on the species, could find only a very few, all in the vicinity of Mt. Ashland. Then, in 2006, his summer-long searches turned up only a single individual. No one has seen Franklin’s Bumble Bee since.

The possible extinction of Franklin’s and the decline of other bumble bees, including the once widespread and abundant Western Bumble Bee, has mobilized efforts to conserve these charismatic and ecologically important insects. To understand the distribution and abundance of all the bumble bee species in Oregon, Washington, and Idaho, the Xerces Society launched the Pacific Northwest Bumble Bee Atlas project in 2018. Hundreds of volunteers have been trained in bumble bee identification, and have logged thousands of hours carrying out standardized surveys in designated grids throughout these three states. Originally planned as a three-year effort, the atlas project has been extended into 2021 and beyond, with special emphasis on searches for the three rarest species: Franklin’s, Western, and Suckley’s Bumble Bees.

I’ve been involved in searching for Franklin’s Bumble Bee since 2015, and have done Atlas surveys in Jackson, Klamath, and Lake counties. This summer, I decided to conduct surveys in SOLC’s wonderful Rogue River Preserve. My first survey, in early June, was carried out near the Corral area, where a large patch of California poppies was attracting many bumble bees. In the 45-minute survey period, I caught 23 bumble bees, most on poppies and a few on the flowers of Himalayan blackberry. Don’t worry, no bees are harmed – they are briefly put on ice to immobilize them for photographic documentation, and then released to resume their bumbling.

The most common species I found, as usual in southern Oregon, was the Yellow-faced Bumble Bee. That’s not a very helpful name, since many species have yellow faces. The scientific name has its own problems: Bombus vosnesenskii. I call them “B-vos” to avoid the tongue-twister. But there was one big, beautiful surprise: a White-shouldered Bumble Bee, one of our most colorful species, and a bee I rarely see in the valley. This was a large queen bee, in her hard-working colony-establishment phase.

Bumble bee colonies produce new queens in the late summer, who emerge, mate, and then find secure spots underground or in other protected sites to overwinter. All the other bumble bees – the established queens, the workers, the males – die by the autumn, leaving the survival of the species totally dependent on these young fertilized queens sleeping through the winter. When they emerge in spring or early summer, the new queens must find a nest site (often an old rodent burrow), lay eggs, and gather all the pollen and nectar to feed their growing larvae. Only after the emergence of the first workers is the queen able to retire from foraging, and remain in the nest to devote herself fully to egg-laying and caring for the larvae.

And what about males, you ask? Queen bumble bees can produce either fertilized or unfertilized eggs. Fertilized eggs are female and become workers; unfertilized eggs are males, and are produced only late in the colony’s life cycle. Males do not contribute to the work of the colony, and are driven out as soon as they emerge. They spend the rest of their lives outdoors, waiting for the emergence of unfertilized young queens. Some of you may have noticed bumble bees sleeping on your garden flowers in the early morning. These are males, who have no home to go back to.

Brown-belted Bumble Bee, Bombus griseicollis — Brown-belted Bumble Bee, *Bombus griseicollis*

Three weeks after my first Rogue River Preserve survey, Kristi Mergenthaler – a fellow lover of bumble bees – let me know that the Douglas Spiraea in the Preserve’s riparian forest was in bloom. I’d asked her to keep an eye on the Spiraea, which is known to be a favored flower for the rare Western Bumble Bee. So I returned for my second survey. Although the two sites were not much more than a hundred yards apart, the hot, sunny oak savanna and the cool, shady forest felt like different worlds. The bumble bees were different as well. In addition to the always-common B-vos, there were four other species. Sadly, no Western Bumble Bees, but there was another surprise. Two of the 21 bees I caught were Brown-belted Bumble Bees, a large species that I rarely encounter west of the Cascades. There is still much to learn about bumble bee habitat preferences and distribution, and areas like the Rogue River Preserve that provide intact natural habitat for pollinators are vital to that effort.

Recently, I participated in the annual “Finding Franklin’s” blitz on Mt. Ashland and other historical sites for the species. Dozens of volunteers spent three days in intensive searches, focusing especially on patches of nettleleaf horsemint and coyote mint, two favorite bumble bee flowers. I’m happy to say that bumble bees were abundant, and we recorded nine species, including three individuals of the rare Western Bumble Bee at Grizzly Peak. But sadly, again no Franklin’s.

Standing in a mountain meadow in the Siskiyous filled with a dizzying variety of wildflowers being visited by thousands of pollinators – bumble bees, other native bees, butterflies – it is hard to imagine why Franklin’s has disappeared. There seems to be plenty of good bee habitat, and thankfully many bumble bee species are still common. After much study, Dr. Thorp and other experts concluded that the decline of Franklin’s Bumble Bee (and of the very closely related Western Bumble Bee) was likely caused by disease.

Nosema bombi is a single-celled fungal parasite that infects bumble bees, often without severe effects. However, certain bumble bee species appear to be highly susceptible, particularly the group that includes Franklin’s, Western, and the European Large Earth Bumble Bee, Bombus terrestris. It is believed that commercial rearing of that European species for pollination of greenhouse tomatoes and peppers led to high levels of infection, which made their way to North America through trade in commercial bumble bee colonies. As a species with a small range and likely low genetic diversity, Franklin’s was particularly vulnerable to a novel disease. Even the formerly abundant Western Bumble Bee virtually disappeared during this same time period. That widespread species presumably had more genetic variability, and seems to be slowly recovering, hopefully reflecting the evolution of disease resistance.

Still, I have to believe that somewhere in the flower-spangled meadows of the Siskiyous there still survive colonies of Franklin’s Bumble Bees, filling the air with a pleasing hum as they bumble from lupine to larkspur, stuffing their pollen sacs and pollinating as they go. It will be such a glad day when we find them again!