Vestal cuckoo bee (Bombus vestalis)

Vestal cuckoo bee on flower
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Vestal cuckoo bee fact file

Vestal cuckoo bee description

GenusBombus (1)

Until recently, cuckoo bumblebees were once considered to belong to a separate genus (Psithyrus) in recognition of their distinctive appearance and their behaviour as parasites in the colonies of other bumblebees. Lately, experts have, by and large, agreed that all bumblebees belong to a single genus, Bombus, with Psithyrus as a subgenus (3). Cuckoo bees are similar in appearance to bumblebees, but they have a softer ‘buzz’, indeed Psithyrus means ‘murmuring’ as opposed to ‘Bombus’, which means ‘booming’. Other differences include the lack of pollen baskets on the legs and a sparser coat of hairs, through which the shiny black cuticle can easily be seen (4).

Psithyrus vestalis.
Female length: 20-24 mm (2)
Male length: 15-19 mm (2)

Vestal cuckoo bee biology

The name cuckoo bumblebee refers to the fact that these bees are brood parasites in the nests of other bumblebees (3). Bombus terrestris (the great earth bumblebee) is the only known host of Bombus vestalis, and the cuckoo’s distribution reflects the predominantly southern distribution of its host in Britain (4), and presumably also throughout its palaearctic range (2).

Cuckoo bumblebees do not have a ‘worker’ caste, like other bumblebees. Instead all the hard work of brood rearing and foraging is carried out by the host colony. Mated female cuckoo bees hibernate through the winter, and emerge in the spring later than their hosts. They feed on flowers for a while before searching out a suitable host nest. They depend on finding, by sight or scent or a combination of the two, a host nest, which needs to be sufficiently advanced to have a worker population large enough to rear the cuckoo bee’s offspring (2). The thick, heavily armoured cuticle of the female cuckoo bee helps to protect her from aggressive encounters with the hosts, who attempt to defend their nest (4). The cuckoo bee may put up with unfriendly attention from workers, and wait for them to calm down, before finding a quiet part of the nest to hide in. Alternatively, there may be a battle in which the cuckoo bee is either successful in killing numbers of workers, and is finally accepted, or is herself killed. After a time of lying low within the host colony, perhaps to take on the scent of the hosts, the cuckoo bumblebee female sets about laying eggs (4). At some stage, she will fight the host queen, who is usually killed (2). She kills host eggs and larvae and uses the wax from host cells to make her own. After the cuckoo bumblebee larvae have developed into pupae and then adults, they leave the host nest and feed on flowers. After mating occurs the females go into hibernation and the males die before the onset of winter (4).


Vestal cuckoo bee habitat

Found in a variety of habitats including gardens and grasslands. Host nests are typically made in old vole or mouse burrows in rough grassland, often beside hedges (6).


Vestal cuckoo bee status

Not currently threatened (2).


Vestal cuckoo bee threats

Although this species is not threatened at present, there has been a dramatic country-wide decline in bumblebees, largely as a result of the loss of large areas of suitable farmland habitats (6). As this species depends on the presence of host colonies, it is affected by declines in the host population.


Vestal cuckoo bee conservation

The Bumblebee Working Group has produced a leaflet called Help save the bumblebee…get more buzz from your garden in order to advise householders and farmers on ways to help the bumblebees (6)


Find out more

For more on invertebrates and their conservation visit:

  1. Buglife, the invertebrate conservation trust:
  2. The Natural History Museum’s Bombus site:

For more on bumblebees visit:

  1. Buglife, the invertebrate conservation trust:
  2. The Natural History Museum’s Bombus site:



Information authenticated by Dr O. Prys-Jones with the support of the British Ecological Society:



In social insect colonies, a group of individuals that are structurally and/or behaviourally distinct, performing certain tasks. Examples are the soldier caste of termites and ants, and the workers of bees.
A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
Stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
The region that includes Europe, the part of Asia to the north of the Himalayan-Tibetan barrier, North Africa and most of Arabia.
Organisms that derive their food from, and live in or on, another living organism at the host’s expense.
Stage in an insect’s development when huge changes occur, which reorganise the larval form into the adult form. In butterflies the pupa is also called a chrysalis.


  1. ITIS, the Integrated Taxonomic Information System (September, 2009)
  2. Prys-Jones, O.E. (2004) Pers. comm.
  3. Natural History Museum Bombus (January, 2004)
  4. Prys-Jones, O.E. and Corbet, S.A. (1991) Bumblebees. Naturalists’ Handbooks 6. Richmond Publishing Co. Ltd, Slough.
  5. The Natural History Museum’s Bombus site: Bombus vestalis (September, 2009)
  6. The Bumblebee Working Group. (2003) Help save the bumblebee…get more buzz from your garden. English Nature, Peterborough.

Image credit

Vestal cuckoo bee on flower  
Vestal cuckoo bee on flower

© Robin Williams

Robin Williams
Kyntons Mead
Heath House
BS28 4UQ
United Kingdom


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