The biology of bumblebee
Bumblebees have got an interesting life cycle which begins in early spring.
With the appearance of the first spring flowers, bumblebee queen's hibernation comes to the end. At that time, she live as a solitary being. While the ground is still covered with high grass, she finds an empty hole. She gathers pollen, on the top of which she lays eggs and warms them with her body. Soon, first workers are hatched and they are even smaller than hanybee workers. In the moment, queen's solitary phase finishes. From now on, she will devote herself only to lying eggs.
At that time, the breeding of drones begins, as well of young queens. That's also the beginning of the end of the colony. Young queens are preparing for the hibernation, while old queens, drones and workers die.

Bumblebees are not dangerous insects. Male bumblebees (drones) don't even have a sting. However, female members of a colony do, and they can release the poison similar to bee poison. Their sting doesn't have a hook, so they can sting more than once. Human organism reacts to the sting by local redness, swelling and itching. All symptoms appear around the sting area and disappear after a few hours.
If allergic to bee poison, a person should avoid situations where there's a possibility of being stung by a bumblebee. In the case of being stung, ask for medical care.