Identification

Bumblebees (Bombus species) have bulky bodies covered by hairs of various colours. Depending on the species, bumblebees may be buff coloured, black with orange-red hairs on the rear end of the abdomen, or black with yellow or yellow and white bands. Male bumblebees may differ in colour from females of the same species.

Bumblebees are social insects and a nest in late summer will contain the old queen bee that founded the colony, and young queens that will mate, overwinter by burrowing in the soil and establish next year’s colonies. Queen bees are fertile females. Worker bees are sterile females and are smaller than queens. The role of the workers is to gather nectar and pollen to feed the grubs, which are reared in wax cells in the nest. The workers also maintain and enlarge the nest initiated by the founding queen and defend it against intruders. Male bumblebees and next year’s queens are produced in late summer.

Size

Queen bumblebees are the largest individuals and are 20-30mm in length. Worker bumblebees can vary considerably in size, even in the same nest. Workers produced early in the season are smaller because they receive relatively little food at the larval stage, compared to those in mid-late summer when the colony is stronger and plenty of nectar and pollen is being brought in. Workers can be 8-20mm long. Male bumblebees are 12-20mm long.

Distribution

Common species are widespread throughout Britain. Some species have a very restricted distribution.

Status

There are 24 species of bumblebee in Britain, six of which are cuckoo bumblebees. Females of these species cannot initiate their own nests but instead take over the nest of another bumblebee species, killing the queen and using the worker bees to raise the larvae of the cuckoo bumblebee. Of the 24 bumblebees, only 12 are common and widespread. The others are in decline. One species, Bombus subterraneus, has become extinct but a continental species, Bombus hypnorum, was discovered in Wiltshire in 2001 and has since become widespread in England.

Habitat preference

Gardens, brown field sites and flower-rich grassland.

Where to find them in the garden

Bumblebee nests are often underground or at ground level but they will sometimes make use of bird nest boxes. Ground-nesting species often take over a tunnel made by a mouse, vole or mole in banks, ditches, hedge bottoms or compost heaps. Adult bumblebees can be seen visiting flowers to collect nectar and/or pollen. The main season for bumblebees is March to October but in recent years, some species, especially Bombus terrestris, has responded to the milder winters by trying to raise nests during the winter. Queens and worker bees of this species in southern England may be seen on sunny days in midwinter visiting the flowers of Mahonia and Clematis cirrhosa whenever the temperature is a few degrees above freezing. It is unlikely that these precocious nests will survive throughout the winter.

Role in the garden

The hairy nature of bumblebees means that they become liberally dusted with pollen when they visit flowers. When the bee moves to another flower of the same species, some of the pollen is transferred to the female part of the flower (the stigma). The pollen grains germinate and grow down to the ovules, allowing fertilization to take place. The plant is then able to set seeds. This process of pollination is essential for many flowering plants, which rely on insects to transfer pollen from flower to flower. All garden fruits, apart from hazel and walnut, need insect pollination.