A cuckoo bumblebee, like the bird it is named after, lays its eggs in another bumblebees 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), and 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.
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, and all species have shortish tongues. Cuckoos have a much harder exoskeleton 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. Apart from that cuckoo bumblebees usually have the same pattern of hair colour as the bumblebees' nests they lay in.
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 larva consume resources but contribute nothing to the nest.
It has been decided to rename the genus of cuckoo bumblebees from Psithyrus to Bombus, so you will find both names in text books.
Bombus fernaldae aka B. flavidus
Notes: Also known as Bombus flavidus
Range: Alaska and Canada south to North Carolina, Tennessee, Colorado, California, usually found in or near forested areas and on the Great Plains.
Body lengths in mm female 17 - 18, male 11 - 15. Hair is medium length.
Range: Ohio south to Florida, west to North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, Tennessee, New Mexico, Mexico.
Body lengths in mm, queen 18 - 22, males 15 - 17. Wings are smoky brown. This bumblebee is a cuckoo of Bombus pennsylvanicus, and is now rare.
Range: Canada south to California, Arizona, New Mexico, Nebraska, New York, Alaska.
Body length in mm. female 16 - 20, male 11 - 16. Hair medium length.
Cuckoo of Bombus appositus, B. fervidus, B. flavifrons, B. nevadaensis, B. ternarius, and occasionally B. occidantalis, B. rufocintus and B. terricola.
Range: Alaska south to California, Utah, Colorado.
Body lengths in mm female 18 - 23, male 13 - 16. Hair is short and even. Parasite of Bombus terricola, B. rufocinctus, B. fervidus, B. nevadaensis, and B. appositus.
Range: Arctic Alaska, Yukon, Northwest Territories, Greenland, Arctic Europe and Asia. Found on tundra
Long tongue, hair long and uneven. Body lengths, queen/female 21 - 24, male 17 - 19.
A cuckoo of Bombus polaris and Bombus baltaetus
Bombus bohemicus, Bombus ashtoni
Bombus bohemicus and B. ashtoni are thought by many to be the same species.
Range: In the US, East, Mid-west and Alaska, also Canada. Found at high elevations in forests. Also native to Europe.
Body lengths in mm, female 17 - 19, male 11 - 17.
Parasite of Bombus terricola, B. affinis and possibly B. occidentalis.
**Images taken from the wonderful https://www.flickr.com/photos/usgsbiml/albums
|North American species|
|North American cuckoos|
|Is it a bumblebee?|
|Other bees1, 2|
|Looks like a bumblebee|