Tree bumblebee

How to recognise it

Unmistakable once known: a ginger-brown thorax, a solid black abdomen, and a clean white tail. No other British bumblebee has that three-part combination.

• Ginger thorax, black abdomen, white tail — a distinctive pattern with no close British equivalent.
• Nesting in bird boxes, roof spaces and cavities above ground rather than underground.
• Groups of males hovering persistently outside a nest entrance in May and June.
• Flies early — often the first bumblebee species to complete its colony cycle, sometimes finishing by July.

Body length 10–18 mm (typically 14 mm).

Biology

Social organisation

Eusocial, colony dies each autumn

A true colony with a queen and workers, but only for one season: everyone dies in autumn except mated new queens, who overwinter alone. Bumblebees.

Colony size at peak

50–400 individuals

Colony lifespan

One season, and a short one — colonies often complete their cycle by midsummer.

Winter

Mated new queens overwinter alone in soil or leaf litter; everyone else dies.

Castes

Queen, Workers, Males, New queens

Nesting

Existing cavities and tubes

Nests above ground, which is what distinguishes it ecologically from most British bumblebees — bird boxes, roof spaces, soffits, cavity walls and tree holes. Old bird nests are a favoured site, and a box that fledged blue tits in April is very often occupied by bumblebees in May.

Carries pollen

Corbicula (pollen basket) on the hind leg

On the wing

March to July

An early and short season. Tree bumblebees are often finished while other species are at their peak.

Lifecycle

1. 1Early emergenceQueens emerge early, often in March, and found nests quickly. The whole cycle runs ahead of most other bumblebees.March onwards.
2. 2Colony growthA fast-developing colony, frequently reaching reproduction by June.
3. 3Nest-surveillance swarmingMales gather and hover in a loose cloud outside the nest entrance waiting for new queens to emerge. This looks alarming, generates a great many phone calls, and is completely harmless — males cannot sting.Several weeks in May and June.

Where it lives and what it does

Habitat

Gardens, parks, woodland edge and urban areas. It is markedly more urban than most bumblebees.

Distribution

Across Europe and Asia. It arrived in southern England in 2001, reached Scotland within a decade, crossed to Ireland in 2017, and is now among the commonest garden bumblebees in much of Britain — a spread of the whole island in under twenty years.

Behaviour

Fast, early and urban. The male hovering behaviour outside nests is the most conspicuous thing it does and the least understood by the public. Its rapid colonisation appears to be driven by its use of above-ground cavities, an underexploited niche in Britain, combined with a short early colony cycle.

Pollination role

A useful generalist pollinator of soft fruit and spring blossom, and one that has added to Britain's bumblebee fauna rather than obviously displacing anything — there is no strong evidence so far that it has harmed resident species.

High on soft fruit and spring blossom, and it is abundant in gardens where those crops are grown.

Honey

Keeps only a few days of stores

A few days' worth of ripened nectar in wax pots, as with all bumblebees. Nothing harvestable.

Relationship with people

How people interact with it

Almost entirely a garden and building-nesting bee, which puts it in more direct contact with people than any other British bumblebee. Its arrival is also one of the best-recorded insect range expansions anywhere, mapped largely through public sightings.

Management

A nest in a bird box lasts six to eight weeks and then empties permanently — the same nest is not reused. Clean the box in autumn and the birds will have it back next spring.

Conservation

Expanding rapidly and not of conservation concern. Its arrival is generally attributed to a combination of climate and the availability of an unoccupied above-ground nesting niche.