Bumblebee’s life cycle

DESCRIPTION

Bumblebees (genus Bombus) are hymenoptera from family Apidae. Being robust insects, their body is covered with silky hair of varying colours depending on the species. They have a small and narrow head, a short tongue and a pair of antennas with olfactory and tactile function. In their thorax are inserted two pairs of membranous wings and three pairs of legs. The third pair of legs has a concavity to store pollen that let them take it to the nest. The female (queens and workers) has a stinger to the end of its abdomen and use it as a defensive weapon. On the other hand, male bumblebees do not have stinger and are harmless.

Bumblebees are eusocial, i.e., their behaviour is characterised for classifying individuals in different castes, the cooperation in the breeding of young and the overlapping of generations. The castes of eusocial insects can be classified morphologically:

• The queen: the biggest female with the longest lifespan, dedicated to lay eggs.

• The workers: daughters of the queen, sterile and smaller than her. They perform the construction and maintenance tasks of the nest, as well as resource provisioning and caring of descendants.

• The males: whose unique mission is to fertilise the queen in the nuptial flight.

LIFE CYCLE

The life cycle of bumblebees begins in spring, when the rise in temperatures cause the queen’s awakening from her lonely hibernation during the winter underground.

After emerging, the queen looks for a suitable place to build the nest, normally holes in the ground, abandoned dens of rodent animals or holes in the trees. Once the nest has been chosen, the queen starts gathering pollen and nectar from the flowers nearby, builds a small mound made of pollen and wax and lays her first eggs on it.

In a few days emerge some larvae that feed on the nectar and pollen collected by the queen. After some weeks the larvae will make a cocoon in which they will become adults. These adults are all female (workers) and will perform all the tasks related to the protection and maintenance of the nest. From this moment, the queen stays inside the nest dedicated exclusively to lay eggs.

During the subsequent weeks the colony will experience a rapid growth with the emergence of hundreds of workers. Before the cold season’s arrival the queen lays some fertilised and unfertilised eggs. The unfertilised eggs will result in male bumblebees (drones), whereas fertilised eggs, better fed, will result in fertile females that will become queens. Normally , the drones are the first to leave the nest and spend their time feeding on nectar and competing to mate. A little later the females leave the nest to mate with the drones, this is known as the nuptial flight.

Afterwards, the fertilised females eat big quantities of pollen and nectar in order to have enough reserves to survive the winter by hibernating underground. These young fertilised queens are the only survivors from the winter and will make a new colony in spring. However, the old queen, males and workers die when the winter arrives.