Our state bee, the rusty patched bumble bee (Bombas affinis) is disappearing just as we are getting to know it.  Historically, the rusty patched bumble bee was broadly distributed across the eastern United States and upper midwest, as well as in southern Quebec and Ontario Canada.  In 2017 the federal government listed it as endangered because their numbers had dramatically declined.  

There are still pockets of the rusty patched bee in Minnesota and Wisconsin and a few other states.  There have been a good number of them reported by citizen scientists in and around the Twin Cities since they were listed as endangered.  August and September is a good time to look for the rusty patched foraging worker bees. 

The exact cause of the decline is unknown, but evidence suggests an interaction between an introduced pathogen and exposure to pesticides, specifically insecticides and fungicides.  Habitat loss and degradation also play an important role.  As bumble bee habitats become increasingly fragmented due to urban development, the size of each population diminishes and inbreeding becomes more prevalent. Inbred populations of bumble bees show decreased genetic diversity and increased risk of decline.

The rusty patched bumble bee is a social species with an annual cycle that starts in early spring when colonies are initiated by solitary queens that emerge from overwintering sites. The queen bee is the only bee that survives the winter.  The cycle progresses with the production of workers throughout the summer, and ends with the production of males and new queens in late summer and early fall. Survival of the rusty patched bee and other bumble bee species require food (pollen and nectar) from abundant floral resources from April through October, undisturbed nesting habitat near floral resources and overwintering habitat for the next year’s queens.  

Two features distinguish the rusty patched bumble from other bumble bees:

1. The rusty patched has a rust or brown or orange colored patch on the second segment of the abdomen going about halfway back. The hairs on the first segment are yellow. The other segments are covered with black hair.

2. The hairs on the thorax of the rusty patched are yellow with a T-shaped area of black hairs.

The rusty patched bumble bee is unique among North American bumble bees in that the queens have a different color pattern than the workers. The queens, which are usually only seen in the spring and fall, do not have a rusty patch or a black thumb-tack on their thorax.

The U.S. Fish and Wildlife Service finalized the recovery plan for the rusty patched bumble bee in 2021. Recovery and conservation of this bumble bee isn’t possible without partners.  Municipalities and private property owners play a crucial role in conservation efforts. 

You can play an important role.

Provide habitat - Rusty patched bumble bee nests are typically 1 to 4 feet underground in abandoned rodent nests or other mammal burrows.  Leave some small areas in your yard bare for the queen bees to start their nest in the spring.  

Don’t use pesticides if you want to encourage bumble bees to nest in your yard.

Plan your garden to provide a diversity of native plants so you will have flowers that bloom during spring, summer and fall.  For example, In the spring, the queen bee emerges to look for nectar and pollen from flowers like virginia bluebells, blood root, wild geraniums, golden alexander and pussy willow.  She will search for a nest close to a diversity of food resources. 

Some summer flowering plants that support rusty patched workers are large beardtongue, slender beardtongue, hyssop, spiderwort, figwort, and butterfly milkweed.

In the fall, the star flowers are goldenrods and asters.  

For more information on this endangered bee and other Minnesota native bees, go to the terrific new website bees mn.org  There you will find close up photos of all the MN native bees, to help you ID them in your yard or nearby park.  You’ll learn about the flowers they use, their nests, and life cycles.  You can also find out how you can be involved in the MN State Bee conservation initiatives. 

Photo Credits: iNaturalist (1), www.fws.gov (2), University of Minnesota BeeLab (3)