Rusty-patched Bumble Bee, Bombus affinis

Excerpted from Bumble Bees of Wisconsin

Rusty-patched Bumble Bee, Bombus affinis This once common bumble bee is the first federally protected species of bumble bee, and first bee to be placed on the endangered species list.

  Physical Description

Hair medium and even. Thorax yellow, with a straight or “T” shaped band of black hair between the wings. First abdominal segment fully yellow, with the second segment yellow and usually containing a patch of orange or rusty-brown hair. Unlike B. griseocollis, this patch is entirely surrounded by yellow hairs. Queens often without the rusty-patch, making the second abdominal segment entirely yellow. Males have similar color patterns to workers, but occasionally with more brown hair on the second abdominal segment. Males also lack corbiculae, or the flattened midleg of the hind leg used for transporting pollen.

  • Queen length: 19-23 mm
  • Female Worker length: 9-16 mm
  • Drone length: 14-17 mm


Rusty patched bumble bee colonies have an annual cycle. In spring, solitary queens emerge and find nest sites, collect nectar and pollen from flowers and begin laying eggs, which are fertilized by sperm stored since mating the previous fall. Workers hatch from these first eggs and colonies grow as workers collect food, defend the colony, and care for young. Queens remain within the nests and continue laying eggs. In late summer, new queens and males also hatch from eggs. Males disperse to mate with new queens from other colonies. In fall, founding queens, workers and males die. Only new queens go into diapause (a form of hibernation) over winter - and the cycle begins again in spring.

  Activity Period

Rusty-patched Bumble Bee activity period Queens emerge in late spring (typically early May), with peak worker numbers in July and August. New queens and drones present from July to September.


Rusty-patched Bumble Bee, Bombus affinis graphic Historically, Bombus affinis was found throughout the upper Midwest and Northeastern United States. Its range has been reduced by over 90%, and is now only found in small pockets, with areas around Madison seeing some of the most consistent numbers in recent years. Other recordings include areas in the driftless, near Milwaukee, and near Baraboo.

  Feeding Habits

Bumble bees gather pollen and nectar from a variety of flowering plants. The rusty patched emerges early in spring and is one of the last species to go into hibernation. It needs a constant supply and diversity of flowers blooming throughout the colony’s long life, April through September.

  Preferred Flowers

 Bee Balm

 Buzz Pollination
 Slo-Mo Footage of a Bumble Bee Dislodging Pollen
 Look Inside a Bumblebee Nest
 How to Build a Bumble Bee House
 Development of Colony and Nest in the Bumblebee

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