bee on black eyed susan

ST. PAUL — A group of roughly 150 Minnesota volunteers spent the last four summers tracking down wild bees in Minnesota to create the state’s first atlas of wild bees living in the state. Volunteers made thousands of observations and took thousands of photographs out of which they identified a diverse range of bee species.

“We've documented 18 bumblebee species of the 23 historically documented in Minnesota,” Britt Marie Forsberg of University of Minnesota Extension and the project coordinator, said.  “It's likely that a handful of those 23 species are no longer in Minnesota, so we've got pretty good representation. Bumblebee conservation is a global concern and monitoring bumblebee populations is providing important information to inform conservation efforts.”

One of the bumblebee species volunteers observed was a three-colored bee called Bombus affinis — also known as the Rusty-patched bumblebee. Bombus affinis, which is the only bumblebee listed as endangered by the U.S. Fish and Wildlife Service, was seen at only four locations in the state over four years. There were two observations in the Twin Cities and one each near Rochester and Duluth.

“Any B. affinis occurrences are reported to the U.S. Fish and Wildlife Service to inform their management and recovery planning,” Britt said.  

One of the bees which had previously been seen in Minnesota but was not found by Bee Atlas surveyors was Bombus bohemicus/ashtoni. That bee parasitizes Rusty-patched nests; and since Rusty-patched bumble bees are extremely rare, B. bomemicus seems to have disappeared from the scene.

A fairly common bumblebee observed by volunteers was a yellow, black and orange Rusty-patched look-alike called the Tricolored bumblebee or Bombus ternarius. Dozens of them were observed up and down the eastern half of the state.

To make nearly 5,000 bumble bee sightings over the four summers, volunteers traveled 25-30 bumble road side routes three times each of the four summers. 

“This involves visiting the route three times each summer and collecting bumblebees for 10 minutes at five different floral patches,” Britt said. “Easily-identified species are tallied and released while more difficult species are photographed and then released.” 

The idea of the Bee Atlas is to not only to count bee species, but to map where in Minnesota each species lives. So the photographs from the road side routes, along with those of a group of volunteer bumblebee photographers, were uploaded by the volunteers into the website iNaturalist.org. The website asks contributors to note where their photograph was taken. The locations of all the volunteer photos established the best current knowledge about the range of the species in Minnesota.

Atlas volunteers didn’t only observe and photograph bumblebees. During the summers of 2016 through 2018, they put out over 120 custom-made wooden bee nesting blocks — or bee traps — across Minnesota. The blocks have a number of different-sized holes drilled in them for non-social solitary bees to nest in.  The holes in the blocks are intended to mimic bee nests which bees would normally build.

“Some solitary bees build their nests in tunnels in wood or stems,” the Atlas website says. “They may utilize existing holes or chew their own. After locating a suitable hole, the female bee begins to build a little room, called a cell, for each of her offspring. As each cell is built, the female stocks it with a mix of pollen and nectar and lays an egg. She then closes the cell and starts on the next one. “

Volunteers were instructed to mount the blocks on a south-facing building, fence post, or dead tree three to five feet above the ground. Then they were asked to observe activity at the box throughout the summer and to take notes on nesting activity. 

“We collected all blocks in the fall, kept them in cold storage to simulate a Minnesota winter, and then raised the temperature in the spring,” Britt said. “The now-adult bees and solitary wasps emerged in our lab and we were able to pin and preserve them for identification. We collected roughly 15,000 specimens.”

Two of the bees which emerged from the bee blocks had never been recorded in Minnesota. They also found a number of species of cuckoo bees which, like cuckoos and cow birds, lay their eggs in the nests of other bee species. The bee blocks also yielded three species of solitary resin bees. Resin bees are important pollinators of flowers like goldenrod, sweet clover and evening primrose.

Volunteers at the Three Rivers Park system in the western Twin Cities metropolitan area were among those who observed and learned about resin bees, bumble bees and cuckoo bees.

“When we learned what little was known on current distributions and species of bees found within Minnesota, it was a no-brainer for us to participate,” Angela Grill, a wildlife biologist for the park system, said. “Three Rivers agreed to help in any capacity we could which included offering locations to install bee blocks and providing staff and volunteers to report observations. We also assisted with locations to host workshops for the general public.”

Grill says knowing which species of bees reside in the park system will help guide decisions of land managers so as to provide the best possible habitat for those species and other wildlife in the park system.

Other biologists and land managers, as well as the general public, can look at and use the Minnesota Bee Atlas via the University of Minnesota’s Bell Museum's Biodiversity Atlas at https://bellatlas.umn.edu.