Cuckoo bumble bees often get a bad rap, and, considering that some of Ontario’s at-risk bumble bees are cuckoos, it’s worth exploring why that is. To begin, let’s demystify what cuckoo bumble bees are all about. These bees are a bit like freeloaders in the insect world—they lay their eggs in other bumble bee nUnests and let the host colony do the parenting. Instead of building their own nests and raising worker bees, cuckoo bumble bees sneak into existing nests, usually causing the unfortunate demise of the host queen. Then, they enlist the help of the host colony’s workers to raise their own batch of offspring, which consists solely of males and new reproductive females. She and her offspring focus on egg-laying and reproduction, leaving foraging and childcare to the original queen’s workers.


A lemon cuckoo bumble bee (left; Photo: Parker Smale) and Fernald cuckoo bumble bee (right; Photo: Cole Blair) female — two of the five cuckoo bumble bee species in Ontario. Note the enlarged and curved stinger displayed here by the Fernald cucko0

  • Being Lazy Foragers
    Since cuckoos rely on the workers from the host colony to do all the foraging work, they’re able to ditch their corbiculae and invest in other, more dangerous adaptations!
Corbiculae: Concave sections of the hind leg surrounded in hairs that hold pollen that bees have collected; also known as pollen baskets
  • Built for Battle
    Relative to their size, cuckoos boast larger and more curved jaws and stingers, turning them into formidable opponents. Their jaw muscles are also stronger than the average bumble bee, so they can bite harder!
  • Tough Hide
    Cuckoo bumble bees have thicker and sturdier sternites compared to regular bumble bees, making them more resistant to harm. This allows them to more easily infiltrate bumble bee colonies without being seriously injured by angry workers.
Sternites: The exoskeleton plates on the underside of the abdomen; the belly of the bee-st
  • Scent Glands
    Bumble bees have scent-producing glands called Dufour’s glands. In cuckoo bumble bee females, the substance inside may help her blend in as one of her host species or repel workers to discourage them from attacking her, with different species using different strategies.
  • Egg Expertise
    With more ovarioles (egg-producing parts of the insect ovary) and smaller eggs, cuckoo females are egg-laying machines, which helps streamline their takeover of a colony.

And yet, are murder machines not worthy of conservation? Of the five at-risk bumble bee species in Ontario, two of them are cuckoo bumble bees: Bombus suckleyi, the Suckley’s cuckoo, and Bombus bohemicus, the Ashton’s cuckoo. These bumble bees are inextricably tied to their hosts, some of which are at-risk themselves, and so monitoring cuckoo populations provides crucial insight into host populations. Moreover, predatory species like cuckoos are necessary regulators of their ecosystems, and so cuckoo conservation is essential to maintaining diversity in broader bumble bee communities.

The truth is that all organisms in an ecosystem, including predators and parasites, interact in complex ways to maintain a balance. Instead of trying to tip the scales when it comes to the inner workings of an ecosystem, conservationists try to focus on the larger, often anthropogenic threats facing species at risk: for bumble bees (of all kinds), these include pathogens and disease (spread from commercial bee colonies), agricultural pesticide use, habitat loss, and climate change. These threats are much larger than cuckoos are, and they’re threats we can address without potentially upsetting entire ecosystems.

Anthropogenic: Directly or indirectly caused by humans

The impacts of cuckoos and predators on bumble bee populations are miniscule compared to the impacts of their major threats: agricultural pesticide use, pathogen and parasite spread from commercial bee facilities, habitat loss, and climate change.



As we contemplate the coexistence of these intriguing bees, it is crucial to shift our focus towards addressing larger threats that jeopardize the well-being of bumble bees at large. Our organization is dedicated to bumble bee conservation, aiming to combat pressing issues such as pathogens, pesticides, habitat loss, and climate change. To join us in this vital cause, we invite you to explore our bumble bee conservation program and consider making a donation. Together, we can safeguard these essential pollinators and ensure the preservation of our ecosystems.

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