by Skip Via
skip@westvalleynaturalists.org
A few weeks ago on a walk through the Bear Paw Battlefield south of Malta, I photographed a bumble bee that I couldn’t identify. The community at iNaturalist agreed that it is an Indiscriminate Cuckoo Bumble Bee. Curiosity peaked once again, I went on a search for more information.
The awkwardly-named Indiscriminate Cuckoo Bumble Bee (Bombus insularis, henceforth known herein as the ICBB) is a member of the Cuckoo bumble bee family (Psithyrus). It is common in northern US states, Canada, and Alaska, usually found in montane areas and meadows but also across taiga and tundra biomes. I have never seen one in the West Valley area and I am not sure that they live here. Distribution maps suggest that we are at the edge of their usual range. I’m including them here because they have such an interesting story.
ICBBs, like other members of the Cuckoo bumble bee family, are social parasites. The ICBB queen will enter the nest of a host species (e.g., white shouldered bumble bee, Nevada bumble bee, both described in articles non our web site) kill the resident queen, and live and breed in that nest attended by workers. They are somewhat distinct from “true” bumble bees in several ways. From Wikipedia:
They are a specialized socially parasitic lineage which parasitises the nests of ‘true’ bumblebees, resulting in the loss of the ability to collect pollen and establish their own nests. Cuckoo bumblebees do not create a worker caste and produce only male and female reproductives. They are considered inquilines in the colonies of ‘true’ bumblebees. (https://en.wikipedia.org/wiki/Psithyrus)
Because they do not build their own nests, they emerge later than other bumble bees in order to give other species the opportunity to establish nests that they can then invade.
ICBBs, unlike other members of their species, are not in decline although they have disappeared from some parts of their historical range. However, many of their host species (especially the Western bumble bee) have seen significant declines in their numbers and ranges due to loss of habitat, pesticides, diseases from domesticated bees, competition from introduced species, and climate change. It is not known if any of these species’ decline is due to the parasitic intervention of ICBBs.
Now that I know what to look for, I’ll be keeping a sharp eye out for ICBBs in our valley. If you encounter one, please let me know.
And if you have never been to the Bear Paw Battlefield, treat yourself someday. It’s a very moving experience.
