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Rusty-Patched Bumble Bee - this is the first bumble bee to be placed on the federal list of endangered species - photo courtesy of the MN DNR

DNR on the lookout for a rare bumble bee

Web posted October 10, 2017
Most people try to avoid bumble bees; Erica Hoaglund goes looking for them.

A biologist with the Minnesota Department of Natural Resources’ Nongame Wildlife Program, Hoaglund is on the lookout or the increasingly rare rusty-patched bumble bee. Earlier this year, it became the first bumble bee to be placed on the federal list of endangered species. In response, states within the bee’s historic range, like Minnesota, have been conducting surveys to get a more detailed picture of its status.

On a warm, sunny morning, Hoaglund and fellow biologist Luke Groff wade into a patch of thistles and other flowering plants in the Sand Dunes State Forest near Zimmerman. The air is still and quiet, except for the chirping of birds in a nearby oak tree and a faint buzzing everywhere. Just the week before, Groff had spotted a rustypatched in the vicinity, the first documented occurrence for Sherburne County in modern times, and the two are hoping to confirm the bee’s presence through further sightings.

Some of Minnesota’s 23 species of bumble bees are easily identified on the wing. Others require closer inspection. Hoaglund holds an open plastic vial about two inches in diameter in her left hand and a cylinder of foam in her right. She brings the two parts of the “squeeze box” together around a bee perched on a flower and pushes the foam into the vial, capturing the insect inside so she can get a good look. After identifying it as a common two-spotted bumble bee, she lets it go, then repeats the process.

“Eastern, half-black, perplexus, tri-colored, brown-belted,” she rattles off an inventory of what she sees. "There’s a gazillion bees out here. They get really focused on the task at hand. I’ve never been stung.”

Before the 1990s, the rustypatched bumble bee was commonly found in 28 states across the Midwest and New England, as well as in Quebec, Ontario and Washington, D.C. Now it’s thought to exist in only about 13 states and Ontario, in scattered locations that represent about 10 percent of the species’ historic range. Places like Minnesota may provide a sort of last stronghold, because of the state’s mix of habitat types.

A number of factors seem to be contributing to rusty-patched bumble bee population declines, including pesticides, pathogens and habitat loss. Climate change may be having an effect, as spring arrives earlier and bees emerge before there are sources of nectar available to them. A Utah researcher believes a parasitic fungus is causing the bees to bloat and grow so fat they can’t mate. Even roads can play a role in bumble bee mortality, as more cars mean more bees are hit and killed.

“We don’t completely know why,” Hoaglund said. “But we’re seeing huge declines and we think it’s likely these different factors are working together and magnifying each other.”

Important pollinators, bees of one sort or another are responsible for helping to produce nearly one-third of the foods we eat. Bumble bees, because of their size and strength, perform what’s known as “buzz pollination” - they rapidly vibrate their flight muscles while on a plant, causing the pollen to shake off the flower. Most other insects can’t do that. It’s a critical type of pollination for some plants with flowers that don’t fully open, such as tomatoes.

Other species of bumble bees, as well as honey bees and other pollinators, also are suffering declines, with the Xerces Society for Invertebrate Conservation estimating that about one-quarter of North American bumble bee species may be at risk of extinction. Taken together, the decline of pollinators could cause what biologists refer to as “cascading effects” and significant declines in a diversity of plants, insects and other animals that depend on each other in a web of complex interactions.

By surveying for rusty-patched bumble bees, biologists such as those in DNR’s Nongame Wildlife Program hope to learn more about their habitat needs and preferences, and thereby better understand what’s causing their decline and how to reverse it. By identifying sites where the bees are currently found, steps may be taken to provide site-specific protections.

“Insects are the most diverse class of macro-organisms on this planet, but probably the one we know least about,” Hoaglund said. “If you’ve ever been stung by a bee, you might wonder why we’d worry about their survival. But if we don’t, our whole ecosystem could be in trouble, including ourselves.”

Minnesota’s Nongame Wildlife Program is funded almost entirely by voluntary donations, especially those made by people when they file their income tax or property tax refund forms. More information can be found at mndnr.gov/nongame. To learn more about rare bumble bees, check out “Bumble Bee Watch,” a citizen science effort to track and conserve North America’s bumble bees, at www.bumblebeewatch.org.

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