Bumblebees or bumble bees, or humble bees) are a group of social and semi-social bees, of the genus Bombus. The genus contains about 250 different species, mostly in the Northern Hemisphere. They can also be found in New Zealand and Tasmania. They occur practically everywhere on the Eurasian landmass.

Most bumblebees live in small groups, which generally last only for a year (though the queen lasts longer). They collect pollen as protein for their young, and themselves eat nectar. They are extremely hairy, with a covering of soft hairs called a pile. It is the female worker bee which one sees out collecting pollen. The pollen is packed into two "baskets" on its hind, very noticeable when full. The baskets are just hairs specially adapted for this function.

Most of them have the same social structure as honey bees do, there is a queen, and there are workers and drones. The usual size of a colony is under 50 members, though some tropical species live in larger colonies.

Bumblebees carry aposematic warning colours, usually some combination of black, red, yellow and white. This is the usual Müllerian mimicry found in bees and wasps. Bumblebees are extremely hairy, and that also is a defence against birds. Young birds, particularly, find them difficult to handle. Some birds are regular predators of bumblebees: the great grey shrike (Lanius excubitor) and the bee-eaters for example.

Life cycle 
Fertilised queens overwinter in a dormant state. They start a nest in the Spring. The nests are smaller, usually much smaller, than those of hive bees. The queen stores sperm from her mating, and can decide whether or not to fertilise an egg as it comes down the oviduct to the vagina. The females are diploid, the males are haploid. This is the common method of sex determination throughout the Hymenoptera.

Only fertilised eggs grow into females, unfertilised ones grow into males. To develop, the larvae are fed both nectar for carbohydrates and pollen for protein.

Queens suppress their female workers egg-laying by aggression and pheromones, until late in the season, when the workers do start to lay eggs. The eggs develop into males (drones) if they are not fertilised (haploid), and females if they are diploid.

Thus the queen will be the mother of all the first males. New queens (those fertilised eggs which are fed on nutritious food) and males leave the colony when they are mature. They mate and the new queens search for a place to overwinter. Then they are dormant over the winter period, starting a new nest in the Spring. That completes the cycle. The queens live a number of years. The workers (unfertilized females) live about a season. Drones live away from the hive(s). Queens do not mate with drones from their own hive.

Bumblebees can fly very high. In 2014, National Geographic said bumblebees can fly higher than Mount Everest.

Nest size 
Nest size according to the species is between 50 and 400 individuals. Colonies have been fiund as small as ~20 individuals and as large as 1700. These nests are small compared to honeybee hives, which hold about 50,000 bees.

Nest types 
Many species nest underground in old rodent burrows or sheltered places. They avoid direct sunlight, where nests might overheat. Other species make nests above ground, whether in thick grass or in holes in trees. Stone-boring bees are found in limestone walls and cliffs, and sand borers are found in compact sand cliffs.

A bumblebee nest is not organised into hexagonal combs like that of a honeybee; the cells are instead clustered together untidily. The workers remove dead bees or larvae from the nest and deposit them outside the nest entrance, helping to prevent disease. Nests in temperate regions last only for a single season and do not survive the winter.

Parasitic bees 
About ten species are called cuckoo bumblebees. These are nest parasites: they specialize in invading and taking over the nests of other bumblebees. In these species, there are no workers. Once such an animal has invaded a nest, it will force the workers to feed it and its offspring. Once the offspring are ready, they will leave the hive, to mate and take over other hives.

Sting 
All bumblebees have a sting, as hive bees do. However, the bumblebee sting does not damage it when used, and they can sting several times. However, they rarely do sting, unless really threatened.

They have an additional type of defence against birds, and that is their mechanical toughness. Birds usually do not swallow bees whole. If they eat bees at all, they manipulate them to eat the thorax alone, for its wing muscles. This is hard to do with a bumblebee, and time-consuming. Generally, they are left alone.

Bumblebees in England 
The BBC has made a number of field reports for its regular Naturewatch  and Spring watch programs. The short film clips have information on:
 Bumblebee flight
 How to tell a hoverfly from a bumblebee
 Bumblebee nests
 Film of animals preying on bumblebees (great tits, crows, mice, squirrels, badgers...)
 Cuckoo bumblebees, which are parasitic on their honey and/or grubs.

BB guide 
 Genus Bombus, the bumble bees. BugGuide.

References 

Bees