Doug says, “Happy Holidays to Bumble Bees!”
I thought winter would be a perfect time to provide some insight regarding our fuzzy, buzzy friends, the bumble bees (Bombus), specifically because these are some of the bees best built to handle cold temperatures, and, in fact, rely on cold winters, preferably with snow cover, to survive and successfully rear a colony.
To understand why chilly temperatures are important for bumble bees we need to understand their life cycle. While many folks are familiar with the perennial colonies of imported western, or European, honey bees (Apis mellifera), fewer know about the life cycles of North America’s native bees, including bumble bees. As beekeepers will tell you, the colony/hive of western honey bees remains year-round, although winter can be rough and significant losses of individuals can occur. So long as the queen survives, numbers can rebound once temperatures increase and more floral resources become available. This, however, is not the strategy of most native bees. In fact, most (~90%) native bees are “solitary” meaning they are not part of a colony, and each female does all the work necessary to create and support their nests. This means that rather than have “worker bees” (non-queen females) gather pollen and nectar for their babies, the female does this and finds, excavates, and creates a nest all by herself—talk about “mom of the year”.
Bumble bees take a little bit from each of these strategies. Unlike honey bees that maintain a colony year-round, the only individuals from bumble bee colonies that stick around past the end of a growing season are the new queens (“gynes”) that mated and are capable of laying eggs the following season. All other individuals—previous season’s queen, workers, and males—perish by late October or November. As temperatures dip, the new queens find a cozy nook or cranny to spend the winter. In many cases, this happens to be in leaf litter (another reason to keep your leaves from fall on-site at your home) and just a tiny bit under the soil—often no more than an inch or so. Some can find winter homes in burrows of other wildlife, but many depend on letting their bodies cool with the ambient temperature to slow metabolism to reserve energy that will be important come springtime.
Come spring bumble bee queens rouse and begin flying in temperatures as low as 50 degrees (F), but she’s built for it. Her fuzziness and ability to “buzz” helps keep her warm. She begins to search for appropriate sites for nesting. Bumble bees are ground-nesters, although many can nest above ground in thatch of bunch grasses, leaf litter, tree cavities, and human structures. Many nests are created in abandoned rodent burrows. Once a nest site is found the queen seeks out floral resources—pollen and nectar—that will replenish her energy and be used to construct the nest cells that comprise the nest. She will create tiny spherical “pots” where a single egg is laid along with provisions (nectar and pollen) for the bee larvae, which will be a female worker bee. Once the first group of workers has matured as adults, they begin taking over the foraging for the queen and she begins to spend all her time laying eggs. Over time the colony grows and can reach numbers of 500 or more, although 100 to 200 is more typical. Once a certain number of workers is reached and the time is right, the queen begins producing males and new queens. These bees will disperse and mate with males and new queens from other colonies, beginning the cycle again.
Now that you have a basic understanding of the life cycle of bumble bees, we can see the importance of promoting healthy habitat. The ground-nesting and winter-use of topsoil and “duff”/leaf litter tells us that sections of land with undisturbed soils are critical to the survival of bumble bees; if we mow, stomp, dig, and/or degrade the land around us then bumble bees and other wildlife that rely on undisturbed ground will decline, which, unfortunately, is something that has been and continues to occur as humans grow more disconnected from “the land”. Additionally, bumble bees need to have access to flowers that bloom from early spring (for queens to establish nests) to late fall (for new queens to build up energy reserves). Checking your property to see when flowers are scarce and then planting native plants that will feed bees during that time of year can mean the difference between a dying colony and a successful one. Setting aside portions of your land for the express purpose of wildlife conservation is one of the strongest actions and statements you can make about your commitment to playing a role in abating the biodiversity crisis. For many bees, populations have plummeted because of nonnative invasive species, habitat loss and degradation, climate change, and pesticide-use. Some species, like the federally endangered rusty patched bumble bee (B. affinis), can now only be found in a small portion (<5%) of their former range (Photo left below). Prior to the 2000’s, rusty patched bumble bee was one of the most abundant bumble bees observed by scientists. Due to impacts of human behavior, the rusty patched bumble bee and many other wildlife no longer occur in Loveland and the rest of Ohio.
Currently, one bumble bee that calls Loveland home, the American bumble bee (B. pensylvanicus), is being reviewed by experts and the U.S. Fish & Wildlife Service to determine if listing it under the Endangered Species Act is warranted (Photo, right below). Like the rusty patched bumble bee, American bumble bee was once very abundant. However, unlike the rusty patched bumble which occupied the Midwest and Northeast, American bumble bee could be found across much of the U.S., hence the name. Now the American bumble bee is showing up less and less in surveys and not being found in certain portions of its range. The Loveland community should consider themselves fortunate knowing that this bumble bee still calls us neighbors, but without serious commitments to improving habitat for pollinators, who can say for how long that will last. In 2023, I will be leading a series of workshops and seminars through Love Our Land to help citizens better understand how to improve conditions on their own properties for pollinators and other biodiversity. The knowledge and skills provided by this series will bring our community a step closer to increasing the quality and quantity of habitat available to our more-than-human brethren. Together we can ensure the protection and conservation of imperiled wildlife. It truly takes us all.
