Bumblebees, belonging to the genus Bombus, are large, fuzzy insects primarily found in the temperate regions of the Northern Hemisphere. They are categorized as eusocial insects, living in cooperative groups with distinct castes and overlapping generations. With over 250 species worldwide, these bees are integral to the health of both wild ecosystems and agricultural systems. Their activities focus on foraging, reproduction, and the annual renewal of their populations.
Their Ecological Role as Pollinators
Bumblebees are exceptional at moving pollen between flowers. Their large, densely haired bodies make them superior pollen collectors, as the branched hairs trap a significant number of grains during a single flower visit. They are generalist foragers, meaning they are not tied to a single type of flower and can visit a wide variety of plant species throughout the growing season.
Bumblebees use “buzz pollination,” or sonication, to access tightly held pollen that other bees, including honeybees, cannot. The bee grabs the flower’s anthers with its mandibles and vibrates its flight muscles at a high frequency without moving its wings. This intense vibration causes the pollen to shoot out of the flower’s poricidal anthers through small pores, coating the bee’s body.
This specialized method is required by thousands of plant species, including commercially important crops in the Solanaceae family like tomatoes, potatoes, and peppers. Buzz pollination significantly increases fruit set in these plants. Their ability to generate their own heat also allows them to forage in cooler temperatures and lower light conditions than many other insects, extending their operational window in the early spring and at higher altitudes.
The Structure of Colony Life
Bumblebee colonies are structured around three specialized castes: the Queen, the Workers, and the Males. The colony is founded by a single Queen, who is the sole reproductive female responsible for laying all the eggs. She controls the colony through pheromones and physical dominance, regulating the behavior and reproductive status of the worker bees.
Workers are non-reproductive females who perform all the colony’s labor, including foraging for nectar and pollen, maintaining the nest structure, defending the colony, and caring for the young. Unlike the rigid age-based division of labor seen in honeybees, a bumblebee worker’s task is often determined by her body size, which can vary up to ten-fold within a single colony. Smaller workers generally remain inside the nest, focusing on larval feeding and brood incubation, while larger workers are more likely to take on foraging duties.
Males are produced later in the season and have only one purpose: to mate with new Queens from other colonies. They do not participate in foraging, nest maintenance, or brood care. The colonies themselves are relatively small, usually housing between 50 and 400 individuals at their peak. They do not produce large stores of honey, instead creating small wax pots for short-term nectar storage.
Seasonal Activity and Reproduction
The life of a bumblebee colony is annual, beginning with a solitary Queen emerging from hibernation in the spring. The foundress Queen forages heavily to replenish her energy reserves. She then seeks out a suitable nesting site, often an abandoned rodent burrow or a cavity underground, where she constructs wax cells to store food and lay her first clutch of eggs.
The Queen incubates these first eggs by generating heat with her flight muscles, a process that speeds up the development of the larvae. These first offspring develop into small female workers, whom the Queen raises entirely on her own. Once these first workers emerge, they take over all foraging and nest duties, allowing the Queen to remain inside and focus solely on egg-laying.
The colony grows rapidly throughout the summer, producing generations of workers. In late summer, a reproductive switch occurs, and the Queen begins to lay unfertilized eggs that develop into Males and a final generation of fertilized eggs that develop into new Queens. These new reproductives leave the nest to find mates from different colonies. After mating, the Males soon die, and the newly fertilized Queens feed intensely to build up fat reserves before burrowing into the soil to hibernate until the following spring. The original Queen and her workers perish as the weather cools in the autumn.