Bumblebee colonies are characterized by their social organization and a distinct annual life cycle. Unlike some other bee species, bumblebee colonies are temporary, typically lasting for a single season. Each new colony is founded by a solitary queen, who undertakes the initial stages of nest establishment and egg-laying alone. This unique structure highlights a specialized approach to social living within the diverse bee family.
The Annual Colony Cycle
The life cycle of a bumblebee colony begins in early spring, when a mated queen emerges from her underground hibernation site. She spends several weeks foraging for nectar and pollen to build her strength and locate a suitable nesting site. Preferred locations include abandoned rodent burrows, thick grass, or even birdhouses, providing insulation and shelter.
Once a nest is established, the queen constructs wax pots to store nectar and a “brood clump” of pollen where she lays her first batch of eggs. These initial eggs are fertilized and develop into female worker bees. The queen incubates the eggs by shivering her flight muscles to generate heat, and she continues to forage to feed her developing offspring.
After the eggs hatch into larvae, they consume the surrounding pollen and grow rapidly. Within two to three weeks, these larvae pupate in cocoons, emerging as adult worker bees. With the emergence of these first workers, the colony begins to expand. Workers take over foraging, brood care, and nest defense, allowing the queen to focus primarily on egg-laying.
As summer progresses, the colony reaches its peak size, which can range from 30 to over 400 individuals depending on the species. Later in the season, the queen shifts from laying fertilized eggs that become workers to laying unfertilized eggs, which develop into male bees. Some fertilized larvae are fed more abundantly, developing into new queens.
These new queens and males leave the nest to mate. As winter approaches, the original queen, workers, and males die. Only the newly mated queens survive to hibernate and start new colonies the following spring.
Roles and Activities Within the Colony
The queen’s primary function is reproduction. Once the first workers emerge, she largely remains in the nest, continuously laying eggs to grow the colony.
Worker bees, all female, carry out the majority of the colony’s daily tasks. Their duties include foraging for nectar and pollen to feed the colony, maintaining the nest by cleaning cells and removing debris, and tending to the developing larvae. They also help regulate the nest temperature and defend the colony from threats.
Male bumblebees, also known as drones, have a singular role: to mate with new queens from other colonies. They leave the nest soon after emerging and typically do not return, spending their time foraging for nectar. Unlike the queen and workers, male bumblebees do not participate in nest maintenance or brood care.
Ecological Contributions
Bumblebee colonies play a substantial role in maintaining healthy ecosystems, particularly through their pollination services. They are highly effective pollinators for a wide array of wild plants and agricultural crops, contributing significantly to biodiversity and food security. Their hairy bodies, with branched hairs, are well-suited for collecting and transferring pollen between flowers.
A unique aspect of bumblebee pollination is “buzz pollination,” also known as sonication. For certain plants, such as tomatoes, blueberries, and cranberries, pollen is tightly held within tubular anthers, requiring specific vibrations to be released. Bumblebees can grasp the flower and rapidly vibrate their flight muscles without moving their wings, causing the pollen to be ejected through small pores. This specialized technique makes them particularly efficient pollinators for these crops, a task honeybees cannot perform.