Lifecycle - Bumblebee Conservation Trust The bumblebee lifecycle (2024)

Spring

Setting up a nest

Every nest starts with a single bumblebee queen. After emerging from her winter hibernation, she must quickly build up her strength by feeding on nectar from spring flowers. Then she searches for a dry, sheltered nest site. Common places include long tangled grass, compost heaps, bird boxes, and abandoned mouse and vole holes.

Once the queen has chosen her new home, she gets cosy by burrowing into whatever nesting material is available to create a small round chamber. This material could be dry grass, old moss, or an old bird or rodent nest.

Eggs

Inside the chamber, the queen produces wax flakes from her body and shapes them into a cup. She fills it with nectar collected from flowers, bringing it back to the nest in a special second stomach. She also collects pollen from flowers, packing it together into a tight clump and laying her first batch of eggs on top. Sometimes – especially later on in the colony – she will pack the pollen into a wax cup called a brood cell. The queen sits on the brood cell, shivering her flight muscles to generate enough heat to keep the eggs warm. She feeds from the little nectar pot when the weather is too bad to visit flowers.

Larvae

After four to six days, the eggs hatch into white, C-shaped larvae. These wriggling offspring munch their way through the pollen that surrounds them. They grow very quickly and shed their skins several times. The queen now faces a tricky balancing act! She must keep the nest warm (a constant 25-32°C) by shivering, or her offspring will die. But she must also leave regularly to feed on flowers and bring back more pollen and nectar. Unfortunately, some nests and queens die at this point.

New bumblebees

After two to three weeks, the larvae spin themselves tough, silky cocoons. Inside, they shed their skins to reveal a hard case – the pupa.

The former larvae dissolve into a soupy liquid before rebuilding themselves into adult bumblebees. The pupae are white and see-through at first, but as they develop, the colours and features of the adult bumblebees can be seen through the pupal skin.

After two weeks, the new bumblebees force their way out of the pupae and then bite their way out of their cocoons. To start, they are weak, soft, and floppy! It takes a day for their bodies to harden and for their damp wings to dry, so they can fly. Their hair also starts out silvery-white before darkening to its normal colours.

The queen’s first batches of eggs all hatch into female workers. This army of daughters takes over the important job of collecting pollen and nectar from flowers, to help feed new larvae and fill more wax pots with nectar.

Early summer

The workforce grows…

The nest grows steadily over the summer. Now the queen has workers to help her, she stays in the nest and focuses her energy on building more brood cells and laying more eggs.

Not all workers collect food from flowers. Some (usually the smaller and weaker bumblebees) stay in the nest to help remove dead larvae or adults, protect the nest against predators, and keep the nest at the right temperature. On hot days, when the nest might overheat, workers use their wings to fan cooler air inside.

With more and more workers collecting food over time, each batch of larvae gets more pollen to eat, producing bigger and stronger adult bumblebees. Workers only live about four to six weeks, so they need to be replaced constantly.

Late summer

Males and new queens

Finally, if the nest grows big enough and the workers collect enough food, the queen starts to lay eggs which hatch into males and new queens.

Once grown, males leave the nest to mate with new queens from other colonies, and never return. They spend their days hanging out on flowers, drinking nectar, and flying around looking for queens.

New queens are fed up to three times more pollen as larvae, making them very big. As adults, they build their strength by feasting on the food stored in the nest, and taking trips outside to feed on flowers. The more energy they can store as body fat now, the better their chances of surviving winter hibernation. Finally, they leave to mate with male bumblebees.

Creating new queens is the ultimate goal of a bumblebee nest. Only queens can start a new nest the following year, carrying the genes of the colony onto the next generation, so the future of bumblebees depends on them! Some nests, however, fail before they can produce queens, as there are not enough flowers to feed on.

Autumn and winter

Hibernation

In autumn, nests die off naturally. This includes the old queen, female workers, and the males who have already left.

Only new queens survive by going into hibernation over winter. Favourite places include holes in rotten logs, beneath stones, or under thick layers of moss on the ground. Many queens dig down into the soil to hibernate.

Queens sleep until spring, when temperatures rise and spring flowers start to bloom. At last they emerge, hungry and (for the moment) homeless, ready to start this cycle all over again!

The Cuckoo bumblebee lifecycle

Six of our 24 UK bumblebees have evolved to have a slightly different lifecycle. This group of bumblebees are known as cuckoo bumblebees and, just like their namesake the cuckoo bird, use the nest of other bumblebees to raise their own offspring.

A female (there is no queen) cuckoo bumblebee enters the nest of a queen bumblebee, where she will hide for a little while. Eventually, the cuckoo female will try to kill the social bumblebee queen so that she can lay her own eggs in the nest.

The queen’s daughters, the worker bumblebees, will then raise the offspring of the cuckoo bumblebee, without realising that they are not related to them.

The cuckoo bumblebee larvae will become new adult female and male cuckoo bumblebees, neither of which will help with nest or foraging duties. They leave the nest to feed and find a mate before the males die off and the females enter their winter hibernation.