Cuckoo Bumblebee

Cuckoo bumblebee resting on a leaf
There are 29 species of Cuckoo bumblebees, representing about 15% of the total bee population

Cuckoo bumblebees are parasites that take over the nests of standard social bumblebees, and take on the appearance of being the freeloaders of our ecosystem. Cuckoo Bumblebees try to get their hosts to do everything for them and not give anything in return. 

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    What Are Cuckoo Bumblebees and How Do They Differ From Common Bumblebees?

    Cuckoo bumblebees belong to the same family as standard bumblebees, but they’re in the subgenus Psithyrus, rather than Bombus. They differ from their cousins in that they can neither rear their brood nor collect pollen and since they can’t reproduce without help, they must invade a nest of regular pollinating bees and lay their eggs there.

    They are known as the parasites of the bumblebee world because they depend on this host colony to rear their brood, and once the eggs hatch, they’ll often destroy the host eggs. The 29 species of Cuckoo bumblebees represent about 15% of the total bee population.

    How to Identify Cuckoo Bumblebees?

    Cuckoo bumblebees are less hairy and have a pointier abdomen. Because they often have to take on a defensive role, cuckoo bumblebees are generally a lot bigger and tougher than their social counterparts. They have harder exoskeletons, a longer stinger, and stronger mandibles, which are the weapons they’ll need when confronting the host queen and worker bees.

    How to Identify Cuckoo Bumblebees
    Female cuckoo bumblebees are unable to produce wax or honey, making them incapable to successfully breeding their brood without stealing the nest of true social bumblebees

    Where Can Cuckoo Bumblebees Be Found?

    Cuckoo bumblebees can be found all over the world, but most of the 29 species are in Europe and the UK. Six species occur in the U.S and Canada. Below are four species of Cuckoo Bumblebees, their host species, and their distribution throughout the world:

    The Variable Cuckoo Bumblebee (Bombus variabilis) is in severe decline and may be extinct. It’s known as a parasite of the American Bumblebee (Bombus pensylvanicus) but sightings are extremely rare. The Field Cuckoo Bumblebee (Bombus campestris) is a parasite of Carder Bumblebees, mainly the Common Carder Bee (Bombus pascuorum). It’s found throughout Europe, and middle and northern latitudes of Asia.
    The Forest Cuckoo Bumblebee (Bombus sylvestris) is a parasite of Bombus pratorum, Bombus jonellus, and Bombus monticola. It’s found in most of Europe and the Russian part of Asia. The Southern Cuckoo Bumblebee (Bombus vestalis) is a parasite of Bombus terrestris. It occurs in much of Europe (with the exception of Scandinavia) and is widespread in England, Wales, and Southeast Scotland.

    How Do Cuckoo Bumblebees Find a Nest?

    Scent plays a large role in not only locating a suitable nest but also in overtaking one.

    During the search for a nest, male cuckoo bumblebees will release a scent that notifies their low-flying female travel partners that a promising prospect is nearby. And then when the perfect host nest is found, the female cuckoo will lurk there for a while to pick up the scent of the host.

    The lurking female cuckoo can either take on the scent by making contact with the nest materials and workers, or she can mimic the chemical cues of the host. These pheromones can be used to fool the host workers to accept her in place of the true queen.

    But before the cuckoo female can overtake the host nest, she must be very careful to ensure that the nest has enough workers to accomplish her goals, but not so many as to be a physical threat. If she times it right, it is likely she will need to kill the host queen to assert dominance over the nest. But if her timing is off, the workers may end up killing the Cuckoo bee

    Once she’s been accepted (or at least, undetected), the cuckoo female will lay her eggs in the host nest so that the workers of the host queen can begin to feed and take care of them. But it’s the cuckoo larvae that must trick the host workers into feeding them. 

    According to research, the workers may lose their ability to recognize which larvae belong to the true queen and which are outsiders. It’s also possible that the cuckoo larvae use their larger mandibles to bite and kill the host larvae so that the workers are fooled by the old bait and switch trick.

    Does the Cuckoo Bee Always Kill the True Queen? 

    It’s well established that the cuckoo bumblebee has the capability to overpower the true queen. She is larger, more powerful, has a longer stinger, and a tougher exoskeleton. The cuckoo bee is in more danger of being attacked and killed by the worker bees.

    Very often, the cuckoo will kill the queen. But some have reported seeing the cuckoo and the host queen cooperating, with the cuckoo incubating both her own and the host’s eggs. And there’s evidence that some cuckoos will just rest a bit in the host nest and not even attempt to overtake the queen.

    However, it’s more likely that either the founding queen or the invading cuckoo will be killed in a battle of wills.

    How Do Cuckoo Bumblebees Reproduce?

    Without a host nest, cuckoo bumblebees would become extinct. The standard bumblebee queen will lay her eggs and protect them in a ball of pollen and self-produced wax. The wax protects the offspring until they are developed enough to make their way out of the wax and pollen ball. 

    But because cuckoo bumblebees are not able to produce the necessary amount of wax, and are not anatomically equipped with a pollen basket (corbicula), they can’t collect enough pollen to make the protective ball, feed the grubs once hatched, or provide the nutrients necessary for ovaries to develop in female offspring. 

    The female cuckoo bumblebee is entirely dependent on the host colony to raise her brood – and she manages to make this happen by deceiving the host colony; she’ll need to trick the colony into performing all of the functions she is unable to do in order to raise her brood.

    Where Do Cuckoo Bumblebees Prefer to Breed and Who Are Their Hosts?

    Cuckoo bumblebees will come out of hibernation around six weeks later than the true social queen. At that time, both females and males are on the hunt for a viable nest. A good nest is one that’s already completed and is in a stage of development that will provide the greatest potential for gain with the least amount of risk.

    While some of the Cuckoo Bumblebee species will decide between two or three host colonies, most will narrow in on a single species. Options are limited because the female must select the nest that has the ideal number of worker bees. Too few workers mean that her brood may not be properly cared for, but too many workers is a safety risk since she could be attacked or killed.

    How Do Cuckoo Bumblebees Reproduce
    Cuckoo bumblebees are solitary bumblebees that take over the nests of standard bumblebees

    Can Cuckoo Bumblebees Produce Wax or Honey?

    The true social bumblebee queen can produce wax and excrete it from her abdomen. She is also able to collect pollen and create honey cups from which both she and her brood can feed. These abilities make it possible for the queen to successfully raise her brood; she has the supplies she needs.

    But the female cuckoo bumblebee is unable to produce wax or honey, and she can collect only enough nectar to provide her with energy when she is on the hunt to take over a nest.

    There certainly wouldn’t be enough pollen or honey to feed her brood, and without wax, she’s not able to protect her eggs until they are ready to hatch. Her many deficits make it necessary for the cuckoo bumblebee to find a host to take on the responsibilities she can’t fulfill.

    Are Cuckoo Bumblebees Beneficial for the Environment?

    Several of the cuckoo bumblebee species are in decline and one is almost certainly extinct or nearing extinction. Should we be concerned about saving a subgenus that actively tries to destroy a colony of “good” bees? It’s natural to view their behaviour and determine that cuckoo bumblebees are dangerous and not worth protecting. 

    Patrick Llhomme, PhD an ecologist who studies cuckoo bumblebees, says that he is not surprised that many are curious to know why they should care about saving bees that are “so mean.” Most people naturally view parasites as unfavourable. But he says that parasites “are not only important in shaping the populations or the behaviour of free-living species, but they are also an integral part of the ecosystem and the complex food web.” 

    Other researchers also note the importance of parasites in driving biodiversity and resilience among dominant species. Some may even play a role in reducing the virulence of bumblebee diseases. Overall, they contribute to a healthy ecosystem.

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