Wild About Utah

First let me set the stage: Not long ago I was hiking in Northern Utah’s Bear River Range. It was the height of wildflower season, and I was enjoying the colorful variety of blossoms along the trail. I stopped to admire a tall, showy plant with dozens of purplish-green blossoms: Frasera speciosa, commonly known as monument plant or green gentian. It’s often seen near the top of Logan Canyon, but what struck me about this particular monument plant was that it was full of bumble bees.

I knew that a Utah-based conservation science organization, Sageland Collaborative, is asking community volunteers to help them measure bumble bee diversity in the state, so I took out my phone and snapped a few photos. Later I uploaded the best photos into an app called iNaturalist so they’d end up in the Utah Pollinator Pursuit database maintained by the Utah Division of Wildlife Resources with Sageland’s help. Then I waited to learn what species of bumble bee I’d seen. The answer came back: indiscriminate cuckoo bumble bee. I thought: What an unusual name. I needed to know more.

It turns out “indiscriminate” simply means that, unlike many native bees that are particular about what they eat, this species doesn’t much care where it gets its nectar. As for “cuckoo”? Like the birds they’re named after, these bumble bees are thieves.

Or to say it more scientifically: these bumble bees are kleptoparasites. Parasites – animals that take resources they need from other species to the detriment of those species – and “klepto,” as in stealing. Like cuckoos or cowbirds, they lay their eggs in the nests of other bumble bee species, letting the workers from the host species do the work of raising them.

Here’s where our crime story gets even more sinister. When a cuckoo bumble bee queen finds a suitable nest to rob – one with a good-sized group of workers to raise the bee larvae, but not so many workers that they can easily protect their queen – she kills the host queen and becomes part of the colony, laying her alien eggs for the host workers to feed.

Cuckoo bumble bees don’t need their own workers, so they’re less often seen on wildflowers. In fact, there’s a good chance that some of the other bumble bees on my monument plant – the ones I didn’t get a picture of – were members of the host species. They also don’t need to take pollen back to a nest of their own, so they don’t have those “pollen baskets” we often see on the hind legs of female bumble bees.

But they do move pollen from flower to flower when it sticks to their bodies as they feed. In other words, they do play a role in sustaining the wildflowers we enjoy every summer. So is this really a crime story? Or is it just another example of the amazing diversity of behaviors found in nature? While you’re deciding about that for yourselves, I hope you get a chance to enjoy watching Utah’s various kinds of bumble bees as they do their all-important work.

I’m Mark Brunson, and I’m wild about Utah’s native bees.

Credits:

Images Courtesy & Copyright Mark Brunson, Photographer
Featured Audio: Courtesy & © Kevin Colver, https://wildstore.wildsanctuary.com/collections/special-collections and J. Chase and K.W. Baldwin. https://upr.org/
Text: Mark Brunson, https://www.usu.edu/experts/profile/mark-brunson/
Additional Reading: Lyle Bingham, https://bridgerlandaudubon.org/

Additional Reading

Wild About Utah pieces authored by Mark Brunson

Sheffield, Cory S., Cuckoo bees, Epeoloides pilosula, The Xerces Society, https://www.xerces.org/endangered-species/species-profiles/at-risk-bees/cuckoo-bees

Smale, Parker, Understanding cuckoo bumble bees: terrors or treasures?, Wildlife Preservation Canada, February 29, 2024, https://wildlifepreservation.ca/blog/understanding-cuckoo-bumble-bees-terrors-or-treasures/

Barth, Amanda, The Unique Lives of Cuckoo Bees, Sageland Collaborative, July 25, 2024, https://sagelandcollaborative.org/blog/2024/7/25/the-unique-lives-of-cuckoo-bees