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Found and Lost: A Rusty Patched Bumblebee Nest- by Mike O’Brien

Updated: Apr 29, 2022

On a beautiful morning this past June I decided to take a hike in the Dobson Blufflands Tract. My walk took a turn on a rarely used trail into a lower forested area where just 2 weeks earlier we had done some buckthorn clearing. While standing there and staring around as I am wont to do, I noticed a bumblebee land on the embankment of the trail near me and crawl into a hole. It had to be a bumblebee nest!

Interestingly, we had not noticed this nest 2 weeks prior nor had the bees attacked us despite using a small chainsaw literally within 2 feet of this nest. My wife and I are volunteers with the Wisconsin DNR “Bumblebee Brigade” which does surveys of bumblebees to document their presence and abundance in the state. Because of this experience I knew that locating a nest of bumblebees would be an interesting find. The experience of doing surveys for a few years has also given me enough knowledge to identify a majority of the local bees including the federally endangered Rusty Patched Bumblebee. As I stood there watching the slow coming and going of the bees I soon realized what I was seeing was a nest of the endangered Rusty Patched. Counting this nest, there have been only 5 well documented Rusty Patched nests that have been found and studied in the last 50 years. So, to understate it, this was good news.

Staff from the DNR soon came to further observe and set up a protocol for daily observations. We were fortunate to have willing staff from not only the DNR but also the Federal Fish and Wildlife Service locally to help with the monitoring.

All was going well until about the second week of July when we noted that instead of the expected steady rise in nest activity, and by inference the hive population, there were gradually fewer and fewer counts of bees coming and going. Just as concerning were the observations of bees tumbling out of the hive having difficulty flying. A couple bees with deformed wings were also observed coming out of the nest and dying at our feet. During the summer researchers from the University of Minnesota placed colored marks on some of the worker bees to try to see where they were foraging but we never saw them in Dobson nor in the gardens immediately adjacent to Dobson. Ultimately the nest ceased all activity in early August. At this time a team led by researchers from the University of Minnesota came down to excavate the nest. Specimens of the now dead bees, bees wax and other components of the nest were taken apart and samples sent to labs across the country for further analysis.

So what happened? The short answer is we don’t know, well, at least I don’t. Nothing conclusive was discovered on testing for infectious causes. The observations of the wing deformities raises the possibility of a type of virus that causes the same problem with honey bees but that was not proven. On the studies of insecticides, Bifenthrin had the highest level in the bees wax. This is an insecticide is found in products such as Ortho Home Defense, Bifen, and many others. However, it is not known if the levels found would be considered toxic to the nest or even to individual bees. Also, some levels of fungicides were found which can be synergistic with insecticides. Lastly, triclopyr and 2,4D were detected in small amounts in the wax. Both of these have been used in the Dobson area as herbicides but they have not been known to be toxic to insects.

A Rusty Patched Bumblebee Foraging

Ultimately the data from the study of this individual nest was not able to highlight any one cause of the decline of the Rusty Patched Bumblebee but it does add another piece of data to the puzzle. Either way, finding the nest and contributing to the observations of this endangered species was fascinating and very rewarding. It is a great example of how doing some simple citizen science can yield some unexpected wonders. I encourage all of you to consider joining one of the many citizen science projects that are available to you. Organizations and websites that might have a project that interest you include the Wisconsin DNR – which has the Bumblebee Brigade, the Audubon Society – with offerings including the upcoming Christmas Bird Count, the Xerces Society, and many others.

Or, join one of the Friends of the Blufflands work outings. You will get healthy exercise, learn about our native species, and maybe even find a Rusty Patched Bumblebee nest!

Mike O’Brien

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