Cuckoo bees - treachery in nature

Alex Worsley

Senior Ecologist

Like their namesake of the avian world, cuckoo bees exploit the industrious work of their host species by becoming brood parasites. There are a wide variety of cuckoo bees. These range from the uckoo bumblebees, which colonise the home of their host and use the inhabitants for their own purposes, to the species found in general. such as Nomada, Sphecodes, Stelis and Epeolus which parasitise solitary bees. All of these bees forgo the collection of nectar to provision nests for their young, preferring to use other species to do the work for them. As such, these bees do not have the pollen ‘baskets’ of bumblebees or the pollen collecting hairs of solitary bees (the scopae).

Although it would be unwise to anthropomorphise invertebrates, they are after all carrying out their natural lifecycles as part of a functioning ecosystem, in human terms the behaviour on display by such creatures could certainly be described as treacherous!

While most bumblebees are viewed as social beings, living in nests founded by a queen and provisioned with ‘workers’ which help collect the pollen and nectar required to raise a new generation of queens and male bumblebees. When it comes to cuckoo bumblebees, their approach is quite different. These rebellious insects don't bother with the whole communal living vibe and prefer more nefarious methods when it comes to raising a brood. Although cuckoo bumblebees often closely resemble their host, they tend to be larger with a more powerful sting and a thicker layer of chitin acting as armour. In keeping with their adapted behaviour some cuckoos have suitable attire, check out the dark gothic wings of the Red-tailed Cuckoo Bumblebee (Bombus rupestris). The females don’t collect pollen like a bumblebee queen would, but invade a relatively new host nest, kill the queen and using deceptive pheromones trick the worker bees in the nest to continue foraging for pollen stores which are then used to feed the interlopers young.

The cuckoos associated with solitary bees act a little differently. There are many solitary cuckoo bees and all are specialised to utilise host species or a suite of similar host species. Nomad Bees from the genus Nomada typically use species of mining bee from genus Andrena as hosts (although other species are used as well). These bees look superficially similar to wasps and are often mistaken as such, with stark black and yellow colouration in many species. Sphecodes, the Blood Bees, tend to target Lassioglossum and Halictus, although once again associations with other species occur. Like the cuckoo bumblebees these have a suitably sinister appearance with their blood red colouration!. Stelis and Epeolus target other species such as Leafcutter Bees (Megachile), Mason Bees (Osmia) and Plaster Bees (Colletes). What these species have in common is that they all invade the host nest. As their hosts are not social, as is the case in bumblebees, there are no workers to do their bidding. Instead, they lay their eggs in the host nest cells where they develop and eat the pollen stores provisioned there. Depending on the species; the host larvae are eaten either by the invading adult bee or their offspring, or starve to death due to the cuckoo species eating the stores provided for them!