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About Bumble Bees

A fuzzy bumble bee with clear yellow and black stripes holds tightly to a cluster of orange milkweed flowers. In the background are richly green leaves.
(Photo: Xerces Society / Sarah Foltz Jordan)

All bumble bees belong to the genus Bombus within the family Apidae. The family Apidae includes the well-known honey bees and bumble bees, as well as carpenter bees, cuckoo bees, digger bees, stingless bees, and orchid bees. Bumble bees are important pollinators of wild flowering plants and crops. As generalist foragers, they do not depend on any one flower type. However, some plants do rely on bumble bees to achieve pollination. Loss of bumble bees can have far ranging ecological impacts due to their role as pollinators. In Britain and the Netherlands, where multiple bumble bee and other bee species have gone extinct, there is evidence of decline in the abundances of insect pollinated plants. Bumble bees are also excellent pollinators of many crops.

 

Nesting

Bumble bees are the only bees native to North America that are truly social. They live in colonies, have different divisions of labor or castes, and have overlapping generations, usually with multiple broods throughout the spring, summer, and fall. However, unlike the non-native, European honey bees, the bumble bee colony has an annual life cycle. At the end of the summer the foundress queen, her workers and male offspring will all die; only the newly emerged, fertilized queens (gynes) survive to hibernate through the winter. In the spring, she will found a new nest that eventually may grow, depending on the species and available resources, to 50 – 500 individuals. Bumble bees need a cavity in which to build their nest. The queens are opportunists, looking for any suitably sized cavity. Sometimes this is above ground, such as in hollow trees, abandoned bird nests, rock walls, or under a tussock of grass, but they mostly nest underground. An abandoned rodent hole is a favorite, as this space is warm and already lined with fur. 

 

On the left, a bee burrows into the ground. On the right, a bee sets up residence in a wooden bird house.
Left: A bumble bee returns to its nest in an abandoned rodent burrow. (Photo: devra / Flickr Creative Commons) Right: Bumble bees are often happy to make their home anywhere, including in this weathered old birdhouse. (Photo: Xerces Society / Matthew Shepherd)

 

Life Cycle

The queen creates the first few brood cells from wax, and then provisions them with pollen and nectar and lays eggs. It will take four to five weeks for the first eggs she lays to emerge as adult bees; these bees become workers, taking on the tasks of foraging and helping the queen tend the growing number of brood cells. Depending on their role in the nest, workers may live for one to two months, by which time there will be more workers to replace them. The queen will continue to lay eggs, and the colony will grow steadily through the summer. At the end of summer, new queens and drones will emerge and mate. Because bumble bees have an annual life cycle, and generally only occupy nest sites for one year. Repeated use of the same nest site would happen only by chance, as overwintering queens do not spend the winter in the nest they were born. Because of this, we encourage folks that find nest sites near their home to try to make space for the bumble bees during the season, rather than attempt to move or exterminate them. Understanding the life cycle of a typical bumble bee colony is the first step in understanding their unique habitat needs.

 

A graphic with a beautiful illustration shows the bumble bee life cycle. Step 1: A queen emerges from hibernation in spring and finds a nest site, such as an abandoned rodent burrow. 2. She creates wax pots to hold nectar and pollen, in which she lays and incubates her eggs. 3. When her daughters emerge as adults, they take over foraging and other duties. 4. In autumn the colony produces new queens and male bees, who leave to find mates. Newly mated queens hibernate, and the rest of the bees die.
(Image: David Wysotski / Allure Illustration)

 

Foraging

Bumble bees are generalist feeders, often the first bees active in late winter (February) and the last in fall (November). Since they are active for so many months, they must be able to forage on a wide range of plant species in a wide range of weather conditions to support a colony. Early season, and late season resources are critical, as these are sensitive times of the year for successful establishment, and reproduction. Some individual bees in the colony choose to forage exclusively on a single species or a limited range of related plant species, effectively becoming specialist foragers. When foraging, the female bumble bee carries pollen in a concave, hairless area surrounded by stiff hairs on her rear legs, known as the pollen basket or corbicula. This basket can be seen clearly when it is empty⁠—and, when full, the pollen ball pressed into it is obvious.

 

Left: A bee with an orange, bulging pollen basket flies towards a pale blue flower. Right: Willow flowers put forth a lot of white tendrils, creating a fluffy oblong shape.
Left: The pollen basket is clearly visible on this bumble bee’s leg. Bumble bees are especially vulnerable early in the season when access to pollen and nectar may be limited and weather way limit foraging time, so it is important to provide early food sources such as willows (Salix spp., pictured, left) and other spring-flowering trees and shrubs. (Photos: Xerces Society / Justin Wheeler)

 

Pollination

Bumble bees are able to fly in cooler temperatures and lower light levels than many other bees, and they perform a behavior called “buzz pollination,” in which the bee grabs the pollen producing structure of the flower in her jaws and vibrates her wing musculature. This causes vibrations that dislodge pollen that would have otherwise remained trapped in the flower’s anthers. Some plants⁠—including tomatoes, peppers, and cranberries⁠—benefit significantly from buzz pollination. In contrast to European honey bees, who make large amounts of honey so the entire colony can survive the winter, bumble bees only make a small amount of honey⁠—just enough to feed the colony for a couple of days during bad weather. Since newly-mated bumble bee queens hibernate, they do not need the vast quantity of honey found in honey bee hives.

 

VIDEO: Vibrating Bumblebee Unlocks a Flower's Hidden Treasure

 

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