Male southern cuckoo bee, Bombus vestalis, a large cuckoo bumblebee with a yellow collar and white tail

Bombus vestalis, a male southern cuckoo bee. kitenet, CC BY-SA 2.0, via Wikimedia Commons.

Bombus vestalis | Cuckoo bee Social parasite Common in the south Subgenus Psithyrus

UK Bee Species

Southern Cuckoo Bee (Bombus vestalis)

Bombus vestalis (Geoffroy, 1785) · subgenus Psithyrus

The southern cuckoo bee, also called the vestal cuckoo bumblebee, is the commonest cuckoo bumblebee of southern Britain. It is the dedicated parasite of the buff-tailed bumblebee, one of our most abundant bees, which is part of why it does so well. The female sneaks into a buff-tailed nest, takes over from the queen, and lets the host workers raise her brood. Trace its range, and its northward spread, on the UK Native Bee Species Map, or set it among the world's bumblebees in the World Bee Atlas.

Quick Facts

Common nameSouthern cuckoo bee

Also calledVestal cuckoo bumblebee

Scientific nameBombus vestalis

AuthorityGeoffroy, 1785

SubgenusPsithyrus (cuckoo bees)

UK statusCommon in the south, spreading north

Queen lengthAbout 20 to 24 mm

Male lengthAbout 15 to 19 mm

ActiveMid-March to autumn

HostBuff-tailed bumblebee

TailWhite with yellow side patches

Worker casteNone; no pollen baskets

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

The buff-tailed bumblebee's shadow

The southern cuckoo bee belongs to the subgenus Psithyrus, the cuckoo bumblebees, which build no nests and rear no workers of their own.^[1] Each British cuckoo bumblebee is matched to a particular host, and the southern cuckoo bee is the special parasite of the buff-tailed bumblebee (Bombus terrestris).^[1] Because its host is one of the most common and successful bumblebees in Britain, the southern cuckoo bee is itself the commonest cuckoo bumblebee across the south.^[2]

A bee on the move north

Long a bee of southern Britain, the southern cuckoo bee is now expanding northwards, has only recently reached Scotland, and was first found in Ireland in 2014, tracking the spread of its buff-tailed bumblebee host in a warming climate.^[3][5]

How to identify the southern cuckoo bee

This is a large cuckoo bee, with females among the biggest of all British cuckoo bumblebees at 20 to 24 mm.^[2] The body pile is deep, neat and velvety black, with a buff or chestnut collar that contains scattered black hairs, and a white tail carrying a bright sulphur-yellow patch on each side at the front.^[3] Like every cuckoo bee it has darkened wings, hairy hind legs with no shiny pollen basket, and sparser hair that lets the black body shine through.^[3] The yellow side-patches fade with age, and the collar can pale to straw.

Each British cuckoo bumblebee is tied to one host. The southern cuckoo bee belongs to the buff-tailed bumblebee, the commonest bee in many gardens.

Telling it from the gypsy cuckoo bee

The southern cuckoo bee is most easily confused with the gypsy cuckoo bee (Bombus bohemicus). The southern cuckoo averages larger and neater, with a collar that contains some black hairs and broad, intense yellow tail-patches; the gypsy cuckoo is smaller and fluffier, with a paler, broader collar lacking black hairs and smaller side-patches.^[3] The two also differ in their hosts: the southern cuckoo bee uses the buff-tailed bumblebee, the gypsy cuckoo uses the white-tailed bumblebee complex.^[1]

24mm

Female southern cuckoo bees can reach 24 mm, matched among British cuckoo bumblebees only by the red-tailed cuckoo bee. They are large, deep-black bees, easily taken for a true bumblebee at a glance.^[2]

Lifecycle and behaviour

Mated females emerge from hibernation in spring, often from mid-March, and can be seen feeding on sallow catkins, white dead-nettle, dandelions and ground-ivy, or flying low over the ground in search of host nests.^[2] When a female finds a young buff-tailed nest with a few workers, she slips inside and lies low until she has taken on the colony scent, then dominates or kills the host queen and takes over the egg-laying.^[1] From then on the host workers do all the foraging and brood care, raising only male and female southern cuckoo bees.^[1][4] In late summer the males are among the commonest bumblebees on thistles, brambles, knapweeds and garden flowers such as lavender.^[2]

Source conflict

Separating the southern and gypsy cuckoo bees in the field is not always reliable. Faded or worn individuals overlap, and definitive identification often needs microscopic checks, such as the relative lengths of the antennal segments or the degree of pitting under the female's tail. Many casual sight records of one species may include the other.^[3]

Why it matters

The southern cuckoo bee is a good news story among Britain's cuckoo bees. Because its host is thriving and spreading, it is one of the few socially parasitic bumblebees that is doing well, and its northward march is a visible sign of climate-driven change in the bumblebee community. A healthy population of cuckoo bees is a marker of healthy host colonies, and of the gardens, grasslands and hedgerows full of flowers that both depend on.

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Frequently asked questions

How do I identify a southern cuckoo bee?

Look for a large, deep-black bumblebee with a buff or chestnut collar, a white tail with a bright yellow patch on each side at the front, darkened wings and hairy hind legs with no pollen basket. Its main confusion species is the gypsy cuckoo bee, which is smaller and fluffier with paler markings.

What is a cuckoo bumblebee?

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

What does the southern cuckoo bee parasitise?

It is the special parasite of the buff-tailed bumblebee (Bombus terrestris). Because that host is so common, the southern cuckoo bee is the commonest cuckoo bumblebee in southern Britain.

Is the southern cuckoo bee rare?

No. It is common and widespread in England and Wales, scarcer in the north, and is currently expanding its range into Scotland; it was first recorded in Ireland in 2014.

When is the southern cuckoo bee active?

Females emerge from mid-March and search for host nests in spring. Males and new females are common from mid-summer into the autumn, often on thistles, brambles and garden flowers.

How is it different from the gypsy cuckoo bee?

The southern cuckoo bee is larger and neater, with a darker collar containing black hairs and broad, intense yellow tail-patches, and it parasitises the buff-tailed bumblebee. The gypsy cuckoo bee is smaller and fluffier with paler markings and uses the white-tailed bumblebee complex. Worn individuals may need microscopic checks.

Does the southern cuckoo bee sting?

Females can sting and use it when taking over a host nest, but they are not aggressive towards people and sting only if handled. Males cannot sting.

Does the southern 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

Host species

Buff-tailed Bumblebee

Bombus terrestrisRead more → Lookalike cuckoo

Gypsy Cuckoo Bee

Bombus bohemicusRead more → Cuckoo bee

Barbut's Cuckoo Bee

Bombus barbutellusRead more →

Sources & references

BWARS (Bees, Wasps & Ants Recording Society). Species account: Bombus vestalis, host (Bombus terrestris), nest takeover and distribution. bwars.com.
Falk, S. Field Guide to the Bees of Great Britain and Ireland, Bloomsbury, with notes for Bombus vestalis (size, pile, phenology, male flowers). Steven Falk Flickr collection.
Bumblebee Conservation Trust. Southern cuckoo bumblebee (Bombus vestalis): identification, separation from B. bohemicus, range expansion and first Irish record. bumblebeeconservation.org.
Benton, T. (2006). Bumblebees. New Naturalist series, Collins (cuckoo bumblebee biology and host relationships).
GBIF Secretariat. Bombus vestalis (Geoffroy, 1785): taxonomy and European distribution. gbif.org.

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