Five years ago, a visiting bee specialist searching for the rare Rusty-patched Bumble bee found it at the Arboretum, later notifying Arboretum gardener and member of the Friends, Susan Carpenter. The Rusty-patched bumble bee (Bombus affinis), placed on the endangered species list this spring, also resides in the Lakeshore Nature Preserve. Susan, who led the Friends Pollinator field trip at the Preserve last Sunday, explained that the Preserve’s patchy landscape of woodland with early spring flowers and open prairie with flowers all summer long is ideal for bumble bees. Of the 14-15 possible species of bumble bees in this part of Wisconsin 13 kinds have been found in the Arboretum. And many of those live in the Preserve.
While the entire state has only 20 or so species of bumble bees, there are 400-500 different species of native wild bees in Wisconsin. 85% of these species are solitary bees. Some are tiny, some are black, some are green. They build their nests in small cavities and cracks or underground, and often emerge the next season. New bees emerge in spring from the eggs laid the previous summer. These solitary bees cannot fly very far, and need about 30 trips to collect the pollen needed for one egg.
In contrast, bumble bees live in colonies, and the queens overwinter. A queen emerges in mid-April seeking for nectar in early wood flowers, even Creeping Charlie, and initiates a nest in leaf piles or in the ground. She stocks the nest with pollen balls as provisions. She lays several fertilized eggs into the pollen balls to produce worker bees, all females. Once these bees emerge they take over the foraging, provisioning and brood care while the queen stays in the nest and creates nectar pots, tiny wax cups filled with pollen balls, and lays and incubates eggs. Throughout the summer she produces several generations of worker bumble bees. Finally, the queen will begin to produce male bumble bees and future queen bumble bees (about 20). At the end of the season the males die. So do all worker bumble bees, and only the new queens stay on and dig into loose soil to go into dormancy, overwinter, and begin a new colony next spring. Already at this time of year we observed male bumble bees perching and buzzing on tall flower stalks to make their presence known to future queen bees.
Bumble bees can surprise you when performing “buzz pollination”. Their steady Bzzz at a lower pitch suddenly agitates to a high pitch bzzz bzzzz, when they cling to the anthers of a flower with their forelegs and noisily vibrate their flight muscles, releasing pollen which collects on their abdomen. The female bumble bees then comb the pollen into the pollen baskets on their hind legs. Males don’t have pollen baskets.
We paid attention to bumble bees working up the stalks of wild white indigo. The bumble bee collects pollen by pressing the keel of the flower downward and then rubbing its hind legs on the exposed anthers. As the bumble bee works its way up the plant stalk, the pollen from the male blossoms at the top of the plant is deposited on the bee and then transported to the next white indigo plant it visits.
While Bumble bees often prefer certain flowers, such as columbine or Monarda or white indigo, they develop deft approaches for extracting the nectar from flowers with very different architecture. For example, they will approach a wild columbine by thrusting their head into the spur of the hanging flower. A rusty-patched bumble bee may perforate the top of the spur and reach the nectar the easy way. On an oxeye sunflower bumble bees forage across the flower head to gather pollen from the many tiny flowers when in bloom. On a yellow cone flower, or culver’s root, or catnip they will work their way around the flower cone or stalk, visiting all the tiny blossoms.
Thank you Susan, for teaching us. What a great show and tell session we had in the Preserve. To learn more about bumble bees visit https://beespotter.org/topics/key/
Gisela Kutzbach and contributors