Bumble bees are social insects that live in colonies, but their entire life cycle is annual. A colony is founded, grows, and dies within a single year, with only new, mated queens surviving the cold months. The creation of new individuals and the assignment of roles within this temporary structure rely on genetics and environmental factors. This yearly cycle determines how new bumble bees are brought into existence, from the first tiny egg to the final adult.
The Annual Cycle and Colony Foundation
The life cycle begins in the spring when a new queen emerges from her overwintering location, often having burrowed into soft soil or leaf litter. She feeds heavily on early spring flowers to build up energy and activate her ovaries for reproduction. The queen is initially a solitary insect, having mated the previous autumn.
After foraging, the queen searches for a suitable nest site, commonly an abandoned rodent burrow or a cavity under grass. She collects pollen and nectar, using wax secreted from her abdomen to build pots for storing nectar and a small brood clump of pollen mixed with wax. Into this initial clump, she lays her first batch of eggs.
The queen must incubate these initial eggs and larvae herself by shivering her flight muscles to generate heat, maintaining the brood between 25 and 32 degrees Celsius. She must leave the nest periodically to forage for food, which is a dangerous time for the developing colony. This first generation of offspring develops into female workers, who then take over foraging and brood care duties, allowing the queen to focus solely on laying more eggs.
Determining Roles: How Queens, Workers, and Males are Made
A bumble bee’s sex is determined by a genetic system called haplodiploidy. Fertilized eggs, which contain two sets of chromosomes, develop into diploid females that become either workers or new queens. Unfertilized eggs, containing a single set of chromosomes, develop into haploid males.
The fate of a female larva—whether she becomes a sterile worker or a fertile new queen—is determined by the environment inside the nest, not genetics. This caste determination is primarily driven by the sheer quantity of food the larva receives during its growth phase. Queen-destined larvae are fed significantly more pollen and nectar by the workers for a longer period compared to worker-destined larvae.
This abundant nourishment promotes a larger body size and triggers hormonal pathways that induce the development of reproductive organs. The production of males and new queens typically begins later in the summer when the colony has reached its peak size. Once new queens have matured and mated, they disperse to find an overwintering site, while the rest of the colony dies off as the season concludes.
The Stages of Development and Emergence
The physical transformation of a bumble bee involves four stages of complete metamorphosis, beginning with the egg. The small, cylindrical egg is laid onto or next to a mass of pollen and nectar inside a wax cell and typically hatches into a larva within three to six days.
The larva is a white, C-shaped, legless, and eyeless grub that spends its entire existence consuming food provided by the queen or worker bees. This is the stage of maximum growth, where the larva molts its skin several times, progressing through four to five instars. The rapid consumption of protein-rich pollen and nectar allows the larva to grow exponentially, storing the energy needed for the next stage of transformation.
After reaching full size, the larva enters the pupal stage by spinning a tough, silken cocoon inside the brood cell. This cocoon protects the prepupa, which is the final larval form, as it undergoes the reorganization of its body tissues. Inside the pupal casing, the insect develops its wings, legs, and antennae, rebuilding itself into the adult form.
This pupal stage is a sheltered period of intense development that lasts approximately two weeks. The entire process, from the queen laying the egg to the final adult bee chewing its way out of the cocoon, is generally completed within a timeframe of three to five weeks. Upon emergence, the new adult bee is initially soft and pale, requiring a few hours for its exoskeleton to harden before it can join the colony’s workforce.