Barbut's cuckoo bee, Bombus barbutellus, a bumblebee with two yellow thorax bands and a white tail

Bombus barbutellus, Barbut's cuckoo bee. James Lindsey at Ecology of Commanster, CC BY-SA 2.5, via Wikimedia Commons.

Bombus barbutellus | Cuckoo bee Social parasite Widespread Subgenus Psithyrus

UK Bee Species

Barbut's Cuckoo Bee (Bombus barbutellus)

Bombus barbutellus (Kirby, 1802) · subgenus Psithyrus

Barbut's cuckoo bee is a cuckoo bumblebee that targets the long-faced garden bumblebees. The female makes no nest of her own; she invades the colony of a garden bumblebee or its larger cousin, takes the place of the queen, and leaves the host workers to raise her young. It mimics its host closely, which makes it one of the trickier cuckoo bees to name in the field. Compare its range with its hosts on the UK Native Bee Species Map, or set it among the world's bumblebees in the World Bee Atlas.

Quick Facts

Common nameBarbut's cuckoo bee

Scientific nameBombus barbutellus

AuthorityKirby, 1802

SubgenusPsithyrus (cuckoo bees)

FamilyApidae

UK statusWidespread but rarely common

Queen lengthAbout 16 to 18 mm

Male lengthAbout 13 to 15 mm

ActiveLate April to September

Main hostsGarden & large garden bumblebee

TailWhite, no yellow at the base

Worker casteNone; no pollen baskets

Kingdom	Animalia
Phylum	Arthropoda
Class	Insecta
Order	Hymenoptera
Family	Apidae
Genus	Bombus
Subgenus	Psithyrus
Species	Bombus barbutellus

A cuckoo in the garden bumblebee's nest

Barbut's cuckoo bee belongs to the subgenus Psithyrus, the cuckoo bumblebees, a group of bees that survive entirely by parasitising the colonies of true bumblebees.^[1][5] Like every cuckoo bumblebee it has no worker caste, no pollen baskets on its hind legs, and only sparse body hair that lets the dark, shiny body surface show through.^[2] The female never gathers pollen and never builds a nest. She visits flowers only to feed herself.

In spring the mated, overwintered female hunts out a small nest of her host, slips inside, and over time dominates or kills the host queen. She then lays her own eggs, and the host's workers carry on foraging and feeding, raising a brood of male and female cuckoo bees that is not their own.^[1]

A near-perfect impostor

Barbut's cuckoo bee resembles its host, the garden bumblebee, so closely that the clearest difference is the shape of the face: almost circular in the cuckoo, but long and elongated in the garden bumblebee.^[1]

How to identify Barbut's cuckoo bee

This is a medium to large cuckoo bee. Females are around 16 to 18 mm long, males a little smaller.^[3] Both sexes carry two yellow bands on the thorax, a broad collar and a fringe across the rear, a yellow band at the front of the abdomen that can vary in strength, and a clean whitish tail with no yellow hairs at its base.^[4] The body hair is short and sparse, the wings are darkened, and the hind legs are hairy rather than carrying a smooth pollen basket, all classic cuckoo-bee features.^[4] On males the facial hairs are black.

Look at the face. A garden bumblebee has a long, horse-like face. Its cuckoo, Barbut's, has a face that is almost round.

Telling it from the other cuckoo bees

The two most similar British cuckoos, the southern cuckoo bee and the gypsy cuckoo bee, usually show yellow patches at the front of the tail, which Barbut's cuckoo bee lacks; its tail is clean white.^[4] Barbut's is also fluffier than the southern cuckoo bee and a little smaller than both the southern and red-tailed cuckoo bees, though dark or worn individuals can still be very hard to separate without close examination.^[2]

Barbut's cuckoo bee has two main hosts in Britain: the garden bumblebee and the closely related large garden bumblebee, both long-tongued, long-faced bees of flower-rich places.^[1]

Its hosts and where it lives

The confirmed primary hosts of Barbut's cuckoo bee are the garden bumblebee (Bombus hortorum) and the large garden bumblebee (Bombus ruderatus).^[1] It occurs in the same wide range of flower-rich habitats as those bees, from gardens, parks and roadside verges to woodland edges and brownfield land, anywhere with a good supply of deep, long-tubed flowers such as clovers.^[4] Across Britain it is widely distributed but never common, thinning out towards the north and reaching into west Wales.^[1]

Overwintered females are on the wing from late April, searching out host nests, with males and the next generation of females flying from July into September.^[1] Adults feed at dandelions, clovers, thistles, knapweeds, scabious and brambles.^[2]

Source conflict

The full host list is debated. BWARS and Falk treat the garden and large garden bumblebees as the confirmed hosts, while some continental studies suggest Barbut's cuckoo bee may also exploit other species such as the tree and early bumblebees, with a longer list of possible hosts proposed.^[1][3] Confirmed British nest records point firmly to the garden bumblebees, so the wider list is best treated as unproven.

Why it matters

A cuckoo bumblebee is a sign of a working ecosystem, not a threat to it. Barbut's cuckoo bee can only persist where garden and large garden bumblebees are nesting in good numbers, so its presence signals healthy populations of those long-tongued pollinators and the deep flowers they need. Growing plenty of clover, vetches, foxgloves and other long-tubed flowers, and leaving rough grassy corners for bumblebees to nest in, supports the hosts and the cuckoo alike.

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Frequently asked questions

How do I identify Barbut's cuckoo bee?

Look for a bumblebee with two yellow thorax bands, a yellow band at the front of the abdomen and a clean white tail with no yellow at its base, plus sparse hair and dark wings. The clinching feature against its garden bumblebee host is the almost circular face, where the host's face is long and elongated.

What is a cuckoo bumblebee?

A cuckoo bumblebee is a member of the subgenus Psithyrus: a bee with no worker caste that builds no nest and collects no pollen. The female invades a true bumblebee colony, replaces the queen, and lets the host workers raise her young.

What does Barbut's cuckoo bee parasitise?

Its main hosts are the garden bumblebee (Bombus hortorum) and the large garden bumblebee (Bombus ruderatus). Other hosts have been suggested but are not firmly confirmed in Britain.

Is Barbut's cuckoo bee rare?

It is widely distributed across much of Britain but is rarely common anywhere, and it is not classed as scarce or threatened. It is most frequent in southern England and reaches into west Wales.

When is Barbut's cuckoo bee active?

Overwintered females search for host nests from late April into early summer, and males and new females fly from July into September.

How do I tell it from the southern or gypsy cuckoo bee?

The southern and gypsy cuckoo bees usually show yellow patches at the front of the tail, which Barbut's cuckoo bee lacks; its tail is clean white. Barbut's is also noticeably fluffier than the southern cuckoo bee. Dark individuals may still need close examination.

Does Barbut's cuckoo bee sting?

Females can sting and use it during nest takeovers, but they are not aggressive towards people and sting only if handled. Males cannot sting.

Does Barbut's cuckoo bee make honey?

No. As a cuckoo bee it collects no pollen and stores no honey, relying on its host colony for food. Only the honeybee makes honey in quantity. Compare cuckoo bees, bumblebees and the honeybee in the World Bee Atlas.

Related species

Primary host

Garden Bumblebee

Bombus hortorumRead more → Host species

Large Garden Bumblebee

Bombus ruderatusRead more → Cuckoo bee

Forest Cuckoo Bee

Bombus sylvestrisRead more →

Sources & references

BWARS (Bees, Wasps & Ants Recording Society). Species account: Bombus barbutellus (Kirby, 1802), including hosts, distribution and biology. bwars.com.
Falk, S. Field Guide to the Bees of Great Britain and Ireland, Bloomsbury, with identification notes for Bombus barbutellus (collar, tail, separation from other cuckoos). Steven Falk Flickr collection.
Buzz About Bees. Bombus barbutellus, Barbut's cuckoo bee: size, hosts and foraging, summarising Benton and Falk.
Bumblebee Conservation Trust. Barbut's cuckoo bumblebee (Bombus barbutellus): identification, hosts and separation from similar cuckoos. bumblebeeconservation.org.
Williams, P.H., Natural History Museum. Bombus (Psithyrus) taxonomy and host associations for Bombus barbutellus. nhm.ac.uk.

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