Cuckoo bumblebee Bombus rupestris
Queen Bombus lapidarius, its host.
Cuckoo bumblebees have often similar colour patterns to their hosts, and this type of mimicry could help them enter a nest. As an example, see above the cuckoo Bombus rupestris and its host Bombus lapidarius. But, given the high levels of aggression involved when conspecific worker intruders try and enter a nest, how do cuckoo females manage to be accepted into the hosts nest? They have another, more recently discovered form of mimicry: chemical weapons. Research by Stephen Martin and collaborators investigated the surface chemicals of 14 bumblebee species, including 5 cuckoos, from the U.K. and Sweden.They found out a striking pattern: several of the cuckoo bumblebees match strikingly their hosts chemical profile, in particular the alkene isoforms, which are species specific. A few species differ from this pattern. These species are probably being involved in a host switch, and instead of mimicking their hosts chemical bouquet, they produce a worker repellent chemical. Workers then will avoid, and therefore won't attack the cuckoo female when she enters the nest. This is the case of B. sylvestris, whose normal hosts, B. jonellus and B. monticola, are quite rare in the U.K. and more commonly attacks the common B. pratorum.
All bumblebee photos taken today.
More information
Küpper, G. & Schwammberger, K. (1995). Social parasitism in bumble bees (Hymenoptera, Apidae): observations of Psithyrus sylvestris in Bombus pratorum nests Apidologie, 26 (3), 245-254 DOI: 10.1051/apido:19950306
Martin, S., Carruthers, J., Williams, P. & Drijfhout, F. (2010). Host Specific Social Parasites (Psithyrus) Indicate Chemical Recognition System in Bumblebees Journal of Chemical Ecology, 36 (8), 855-863 DOI: 10.1007/s10886-010-9805-3