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Cuckoo bumblebees are a few species of bees which live parasitically in the colonies of other bumblebees and have lost the ability to collect pollen (Figure 45).. Before finding and invading a host colony, a Psithyrus female (there is no caste system in these species) will feed directly from flowers. Once she has infiltrated a host colony, the Psithyrus female will kill or subdue the queen of that colony and forcibly (using pheromones and/or physical attacks) "enslave" the workers of that colony to feed her and her young. This female also has a number of adaptations, such as larger mandibles and a larger venom sac that increase her chances of taking over a nest.
Cuckoo Bumblebee. Image Courtesy of Alvesgaspar.
Queen and worker bumblebees can sting, but unlike a honey bees, a bumblebee's stinger lacks barbs, so they can sting more than once. Bumblebee species are normally non-aggressive, but will sting in defense of their nest, or if harmed. Female cuckoo bumblebees will aggressively attack host colony members, and sting the host queen, but will ignore other animals (including humans) unless disturbed. Based on my numerous encounters the sting of the bumble bees is considerably more painful than that of a honey bee.
Bumblebees are important pollinators of both crops and wildflowers. Bumblebees are increasingly cultured for agricultural use as pollinators because they can pollinate plant species that other pollinators cannot by using a technique known as buzz pollination. For example, bumblebee colonies are often emplaced in greenhouse tomato production, because the frequency of buzzing that a bumblebee exhibits effectively releases tomato pollen which is normally wind pollinated and therefore difficult to release from the anther.
Bumblebees are in danger in many developed countries due to habitat destruction and collateral pesticide damage. In Britain, until relatively recently, 19 species of native true bumblebee were recognized along with six species of cuckoo bumblebees. Of these, three have become extinct, 