Bumblebees in a changing world

Written July 24, 2013, published in late July 2013

In mid July, Dr. Jamie Strange, USDA-ARD Logan Bee Project, who studies bumblebees, taught a half day workshop on bumblebees and a seminar on pollinator declines across North America at Ft Clatsop, Lewis & Clark National Historical Park. More than one dozen people spent an afternoon learning how to work with bumblebees in the field, including safe handling (hint: clear plastic vials, a net and an ice box), how to identify local species in the field, and life cycle information. Participants included park and refuge staff, interns, a college professor, a beekeeper, and local natural history enthusiasts, all of whom share an interest in pollinators and bees. 

Dr. Jamie Strange talking about key bee identification features before sending the class out to catch bees. Julie Tennis, seated facing him, is a local beekeeper. Photo by Kathleen Sayce.

There are fifty species of bumblebees in North America, from Mexico to the northern boreal forests across Alaska and Canada, at low to high elevations, and thirty-eight species in the continental United States. Bumblebees form two distinct populations, living in the east or the west, with a few small areas where some eastern and western species overlap, such as the Black Hills of South Dakota. All overwinter as young queens, who form their own colonies each spring or early summer. In the late summer, virgin queens and males emerge; after mating, queens hibernate for the winter. Only the young queens overwinter; old queens, workers and males die each fall. Bumblebees can sting without dying, unlike European honeybees, but they tend to be placid, calm bees, and rarely sting even when severely provoked. 

As the initial orientation ended, the sun came out and the bees and novice bee collectors immediately went active at Netul Landing, where the class was held out of doors. Five species of bumblebees were collected in less than twenty minutes; many other bee species were seen, including leaf cutter bees and European honeybees, along with butterflies, dragonflies, wasps and other insects. Dr Strange had predicted that Bombus caligulinosus, obscure bumblebee,  would be the common species for the day, but to his pleased surprise, another normally rare species was almost as common, B. californica, California bumblebee. Also found were B. mixtus, fuzzy-horned bumblebee,  B. vosnesenskii, yellow-faced bumblebee, and B. flavifrons, yellow-fronted bumblebee. Bumblebee species emerge at different times of the year; some come out of hibernation in warm early spring weather, but midsummer is a good time to see most of the local bee species. 

As nets were gently maneuvered to capture bees, discussions continued about bee life cycles, when different species are active, and how to promote bees in home gardens: plant bee food plants and house bumblebees.  These bees often use abandoned vole tunnels in the ground, and in the wet Pacific Northwest, may also occupy tree holes, holes in eaves, walls or birdhouses, which led to a discussion on how to remake birdhouses for bees: Small entry holes, under ¾ inch diameter, and filling a bird  house with loose dry moss may help encourage bumblebees to nest in birdhouses. 

A freshly caught yellow-faced bumblebee, Bombus vosnesenkii, a still-common western bumblebee.  Photo by Kathleen Sayce.

Vials with bees were chilled for a few minutes to slow them down, after which they could be handled easily. No one was stung, and except for a few bees that were preserved for study, all the bees survived.  We got close looks at the five species that were active that day, and then watched as one by one they warmed up and flew away. 

That evening Dr. Strange gave a talk on pollinator declines across North America. Bees, butterflies, bats, and birds that pollinate flowers have all experienced declines in their numbers in the past couple of decades, throughout the continent. In many cases, specific pollinators have disappeared from sites, to be replaced by other species. The reasons are complex, but loss of habitat is a recurring cause. Pesticides and introduced diseases and pests also play parts. More than thirty percent of European honeybee hives die each winter. Over last winter, the average across North America was thirty-two percent.  

Vials and cold box, ready to chill bees for a closer look. Photo by Kathleen Sayce.

Home gardeners can help with foraging and nesting habitat for bees. We have many species of native bees, some of which nest in the ground, some in hollow woody stems, some in wood piles. All bees feed on flowers, eating both nectar and pollen. Planting good bee flowers, like sages, mints, penstemons, clovers, native perennials, and even common yard weeds helps our bees.  Avoiding insecticides, especially neonicotinoids, which are especially toxic to bees, is important. In a recent incident in Wilsonville, Oregon more than fifty thousand bees were killed after flowering linden trees were sprayed with a neonicotinoid pesticide to kill aphids. No one got up that morning and said 'I'm going to kill bees today,' the massive bee deaths were unintended. It may take years for the local population of bumblebees to recover. 

Dr. Jame Strange and Nancy Holman look at two very different bee species. Between them is Jamie's traveling bee specimen box, with nineteen North American bumblebee species. Photo by Julie Tennis.

Jamie Strange's research includes regular resurveys of sites to see how bee populations are maintaining themselves. He looks at low and high elevation species, studying their response to climate change. Some species are moving up in elevation. Others are dispersing to new habitats. More often, formerly common species vanish, to be replaced by others. A rare bee with limited geographic range died out in the past decade, and a more common bee took its place. 

There are websites that promote bee and pollinator diversity. Pollinator Partnership is located at http://www.pollinator.org, where a field guide to western bumblebees can be downloaded, or a print copy purchased. Xerces Society is one of the oldest insect diversity support organizations; it began a couple decades ago in Portland, Oregon; website http://www.xerces.org. These are just two of several pollinator resources on line. 

In my own garden, I plant more native flowering plants every year. Now I'm going to focus more on those flowers that bees feed on. And the next time we make birdhouses, we'll modify a few just for bumblebees.