Cuckoo bumblebees

What is a cuckoo bumblebee? - Differences between cuckoo bumblebees and queen and worker bumblebees. - U. K. cuckoo bumblebees - American cuckoo bumblebees

What is a cuckoo bumblebee?

A cuckoo bumblebee, like the bird it is named after, lays its eggs in another bumblebee’s nest and leaves the workers of that nest to rear the young. Of course the eggs she lays are either females or males (there are no queens). The cuckoo females emerge from hibernation in late spring or early summer, much later than ordinary bumblebee queens. So by the time the cuckoo females have emerged the bumblebee queens will have already established their nests. Cuckoo bumblebees usually have the same pattern of hair colour as the bumblebees' nests they lay in.

Differences between cuckoo bumblebees and queen and worker bumblebees

The cuckoo differs physically from ordinary queen bumblebee in that:

She has no pollen basket on her rear legs
Does not exude wax from between her abdominal segments
Is slightly less hairy than ordinary bumblebees
All species have shortish tongues.
They have a much harder body than normal bumblebees
And because no wax is exuded there are no weak points between the abdominal segments, so if there is a fight between a cuckoo and another worker or queen it is almost impossible for the queen or worker to force her sting into the cuckoo body
They also tend to have a more pointed abdomen, and because they are less hairy the tip of the abdomen is often visible.

It is thought that the cuckoo females locate an established nest by smell. She may go right in and sting the existing queen to death then lay eggs, or she may sneak in the nest and hide for a few days until she smells the same as the nest, then lay her eggs. Whatever method she uses it spells the beginning of the end for the nest because the cuckoo larvae consume resources but contribute nothing to the nest.

It has been decided to rename the genus of cuckoo bumblebees from Psithyrus to Bombus.

Cuckoo behaviour

Cuckoo bumblebees do not forage as industriously as workers or queen bumblebees as they have no-one to provide food for but themselves. In fact their behaviour, before entering an established nest, resembles bumblebee males. They drink some nectar and then just laze around until they are hungry enough to drink more.

U K cuckoo bumblebees

Female

Male

Bombus/Psithyrus rupestris

Rare and not recorded in Scotland. She takes over the nests of Bombus lapidarius. Has darker wings than Lapidarius. Body lengths, female 22 mm, male 16 mm.

Female

Male

Bombus/Psithyrus sylvestris (Forest cuckoo bumblebee)

Common and takes over the nests of Bombus pratorum and jonellus. Body lengths, female 15 mm, male 14 mm. Males tend to patrol mating circuits within 1 m of the ground.

Female

Male

Bombus/Psithyrus bohemicus

Common and takes over the nests of Bombus lucorum. Body lengths, female 19 mm, male 16 mm.

Female

Male

Bombus/Psithyrus vestalis, (Southern cuckoo bumblebee)

More common in the south, and not recorded in Scotland*. She takes over the nests of Bombus terrestris. Body lengths, female 21 mm, male 16 mm.

*It has recently been confirmed that this bumblebee was found in southern Scotland in the summer of 2009.

Female

Male

Bombus/Psithyrus barbutellus

Common and takes over the nests of Bombus hortorum. Body lengths, female 18 mm, male 15 mm.

Female

Male, light form

Male dark form

Bombus/Psithyrus campestris (Field cuckoo bumblebee)

Common and takes over the nests of Bombus pascuorum. Body lengths, female 18 mm, male 15 mm.

Many of the images on this page were taken from Prys-Jones and Corbet's excellent book Bumblebees. As you can see the cuckoos resemble the species whose nests they take over.