Rare, Endangered Bumblebee Sighted in Dubuque

Mowing to Monarchs program supports two threatened insect species

When the creators of “Mowing to Monarchs” (M2M) developed the program, their goal was to provide native habitat for the beloved monarch butterfly, whose numbers are plummeting. But now, these prairie plantings all around Dubuque have proven to support another endangered insect: the rusty-patched bumblebee.

The rusty-patched bumblebee (Bombus affinis) was designated as federally endangered in 2017 by the U.S. Fish & Wildlife Service. One of about 21 bumblebee species in the eastern United States, the rusty-patched was once abundant and widespread. It experienced a steep decline in the years leading up to 2017, which the FWS attributes to an introduced pathogen as well as pesticide use.

The famously migratory monarch butterfly is also struggling due to habitat loss and the widespread use of pesticides and herbicides. In particular, the monarch relies exclusively on milkweed to lay its eggs and as the sole food for caterpillars. Although the monarch population is threatened, the butterfly is not yet protected under the Endangered Species Act. Assessments are ongoing. However, the International Union for Conservation of Nature (IUCN) added the monarch to its Red List of threatened species in July 2022.

Mowing to Monarchs (M2M) aims to support the diminishing monarch population by providing native plants and education to local homeowners so they can create their own small “pocket prairies” and larger “prairie meadows.” Program partners include the Dubuque County Conservation Board and Master Gardeners of the Dubuque County Extension Office of Iowa State University.

Rusty-Patched Bumblebee Sightings

Pollinator enthusiasts Jennifer Agee and Doug Cheever both spotted rusty-patched bumblebees in their M2M prairies late this summer.

“I’ve been watching for B. affinis since they were confirmed in a preserve in Jo Daviess County last summer,” Jennifer Agee said. “That’s not too far away as the bee flies. But to find one in my own M2M pocket prairie—that was really exciting.”

Agee submitted photos to the Xerces Society for Invertebrate Conservation, where a biologist confirmed her first sighting. She also submitted photos to bumblebeewatch.org, a Xerces citizen science site that provides essential data to the FWS.

“I spotted at least three individuals over the course of two weeks,” Agee said.

Doug Cheever, an M2M supporter and educational “coach” for participants, was also delighted to find rusty-patched bumblebees at work in his pocket prairie. “They seem to love anise hyssop,” he said, referring to one of the native flowers provided in the M2M native plantings. He, too, saw several individuals in late August, including two male bumblebees that spent a cold night tucked under a flower.

Identifying the rusty-patched bumblebee takes a bit of practice. “Most bumblebees look pretty similar,” Agee admitted. “What’s distinctive about the rusty-patched is that it has an extra yellow segment with a little reddish-brown spot just below the wings.”

If they’re so similar, what’s the big deal?

“For one thing, it’s just exciting to have an endangered species thriving on your own property,” Agee said. “It makes you feel like maybe you can make a difference.” The rusty-patched bumblebee is a bellwether for other native bees and insects like fireflies, which are struggling due to pesticide use and light pollution, she said.

“We need a culture change where we learn to embrace more native plants, like milkweed and hyssop, and step back the spraying, trimming, and weeding.”

If you like tomatoes, you love bumblebees, she pointed out. Bumblebees provide “buzz pollination,” a special vibration that allows certain flowers to release their pollen. Tomatoes, blueberries, and several other human favorites require buzz pollination to set fruit.

Bumblebee Life Cycle

Unlike honeybees, whose colonies survive the winter, all but the new queen bumblebees die out every fall. In late summer, new queens mate and then bury themselves in the earth or ground litter to hibernate. When they emerge in the spring, each surviving queen must find a nest location (often an abandoned rodent nest or clump of plant debris), as well as enough pollen and nectar to lay eggs and feed the new generation to adulthood. After that, the workers take over food-foraging efforts for the summer.

This makes spring a critical time for all bumblebees, including the rusty-patched bumblebee. “If an emerging queen can’t find a nesting site or enough early flowers, she won’t establish a colony, and a whole generation can be lost,” Agee explained.

“Low Mow May” is a movement gaining traction in Dubuque that aims to support pollinators by encouraging homeowners to wait until June before mowing their lawns. Early flowers, including natives but also pollen-rich weeds like the dandelion, are essential to supporting bumblebee queens in the intense effort required to establish a colony.

But right now in the autumn, conservationists are recommending that everyone “Leave the Leaves,” explaining that pro-pollinator homeowners should resist the urge to clean up fall leaves and other standing dead plant material. “One of the most valuable things you can do to support pollinators and other invertebrates is to provide them with the winter cover they need,” according to Xerces. “Leaves are not litter. They’re food and shelter for butterflies, beetles, bees, moths, and more.”

From Mowing to Monarchs—and Rusty-Patched Bumblebees

“There’s so much to celebrate about the M2M program,” said Marilyn Norman, a master gardener and coach for Mowing to Monarchs. “In just three years, nearly 200 landowners in Dubuque County have planted 120,000 square feet of prairie. These native plants are drought- and erosion-resistant. They are beautiful, and they support much-needed wildlife, including two beloved threatened species.”

Kaytlan Moeller, Outreach Coordinator for Dubuque County Conservation, agrees. “If we all work together to do our part, we can shift the cultural norm that manicured turf grass is all that your yard can be. It’s more than that. It needs to be more than that,” she said. “Our yards can help rebuild biodiversity, improve water quality, sequester carbon, and still be beautiful. What can you do with your space?”

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