Rusty patched bumble bee

Rusty patched bumble bee on a Culver’s root at the University of Wisconsin–Madison Arboretum.

Sightings of Minnesota’s state bee continue to excite bee surveyors in the Twin Cities metro who say the endangered pollinator has recently been spotted in residential gardens and other urban landscapes.

The rusty patched bumble bee, formally named bombus affinis, landed on the U.S. Fish and Wildlife Service’s endangered species list in 2017.

The rusty patched bumble bee’s population has declined by an estimated 87% over the past 20 years, according to the agency. Today, the bee is believed to be present in only 0.1% of its historical range.

Angela Grill, a wildlife biologist with Three Rivers Park District, spends each summer looking for the rusty patched bumble bee in the roughly 27,000 acres of land managed by the park district throughout the Twin Cities.

Grill said finding the rusty patched bumble bee in the park district’s vast restored prairies is like finding a needle in a haystack — yet, bee researchers continue to hear of sightings of the bee in smaller gardens in highly-developed areas.

“It’s kind of puzzling I think to researchers right now,” she said.

In Burnsville, for example, sightings of the rusty patched bumblebee have been documented in some residential gardens, according to Linnea Wier, a senior natural resources and forestry technician with the city.

Grill said researchers trying to understand rusty patched bumble bee sightings in the Twin Cities area are trying to balance two unknowns; why the bees choose the locations they choose and how much of our information is shaped by differing research methods.

“I think there’s still a lot of unknown and lessons to be learned that researches are trying to figure out,” she said.

While small pollinator gardens can be a surprising draw for the rusty patched bumble bee, large-scale conservation efforts have also proven beneficial.

Surveyors in Burnsville discovered the rusty patched bumble bee in 2018 and again spotted the bee in city parks in 2019. Last year’s survey confirmed the bee’s presence in two additional city parks after park-goers reported sightings.

Wier said a two-acre area where the city completed a turf-to-prairie conversion project is one of the locations where the bee has been sighted — she said it’s especially exciting to find an endangered species in an area that wasn’t previously providing any resources to bumblebees.

On Three Rivers land, Grill said bee surveyors had a great year in 2018 when they found rusty patched bumble bees in seven park locations.

Rusty Patched

A rusty patched bumble bee on a wild bergamot flower.

The next survey, completed in 2020, only found three rusty patched bumble bees at two locations; over 2,000 bees were captured and identified.

Interestingly, a manicured garden property in Hennepin County is one place the surveyors have had luck spotting the rusty patched bumble bee year-after-year.

This year’s Three Rivers surveys are ongoing.

While Grill remains hopeful, the threat of extinction facing the bees is always close at mind.

“I always can’t help but think in the back of my head, ‘is this the last one — is this the last one I might ever see in my life?’” Grill said. “Because that’s where we are at with some of these declining pollinators.”

Research challenges

Grill said the decline of the rusty patched bumble bee is driven by more factors than just habitat loss, but researchers have very few opportunities to observe the bees and their nesting sites.

“They are at such low numbers that even doing research on them is extremely difficult,” she said.

Insecticide and pesticide use in agricultural areas could explain the push of these pollinators towards the metro, she said. Other factors affecting their populations are thought to be diseases and climate change.

This year’s drought, for example, is altering flower bloom times and causing widespread wilt.

Despite the challenges of bee research, the observations of average citizens can make an important difference.

Last year, a Minnesota resident who spotted a rusty patched bumble bee nest at their residence helped University of Minnesota researchers observe the bee’s nesting behaviors for the first time in over 25 years.

Think you’ve spotted a rusty patched bumble bee or other rare pollinator?

Apps, such as iNaturalist and Bumble Bee Watch, can help citizen scientists report their findings to the experts by uploading photos. Grill said iNaturalist photos captured at a Three Rivers property, for example, are sent to her for review.

But patience might be the key for bee enthusiasts hoping to spot the rusty patched.

Jon Allen, the city of Savage’s longtime parks and natural resources superintendent, said he hasn’t encountered the rusty patched bumble bee, despite visiting the city’s pollinator-friendly sites almost every day.

Bumble bee — Savage Environmental Learning Center

A bumble bee visits a flower at the McColl Pond Environmental Learning Center pollinator gardens in Savage.

But, with documented sightings in Burnsville, Allen said he believes they are probably also in Savage.

“It’s just a matter of being fortunate enough to observe them,” he said.

Planting for pollinators

Heather Holm, a Minnesota biologist, pollinator conservationist and author, says the rusty patched bumble bee can be observed by people who are looking for them in the metro — and backyard habitats play an important role.

During a workshop with Burnsville residents this month, Holm said the way to support bumble bees in a home garden is by ensuring pollen and nectar resources are available to pollinators throughout the growing season.

Avoiding pesticides by building a tolerance for your garden’s imperfections is also key, she said.

For early spring, Holm recommends native perennials such as Dutchman’s breeches, bluestar, waterleaf and American bladdernut to provide adequate nutrition for bumble bees that’ve emerged from their hibernicula after a long winter.

During this critical period, the queens need fuel as they look for a place to nest.

In late spring, native plants including partridge pea, false indigo, prairie clover and lupine offer good resources for bumble bees, Holm said.

In mid-summer, male bumble bees need nectar; Holm recommends milkweed, coneflower, Joe-Pye weed and thistle.

At the end of the season, goldenrod, blazing star, Joe-Pye weed and wild bergamot help bees build up their fat storage before hibernation.

Local residents working with a smaller space, such as an apartment deck, can also support pollinators.

Holm said native perennials can last around three to four years in large containers, and single-flower annuals — such as cosmos and zinnias — are also beneficial.

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