In honour of World Bee Day, May 20, 2025.

A friend recently asked me about cuckoo bees, as if the term referred to a single species. Not at all! Cuckoo bee is a term used for a cleptoparasite, a bee that steals food or prey from another bee. Cuckoo bees lay their eggs in the cells or nests of other bees, so that their larvae grow up on food stolen from the host bees. This means that the host bee larvae do not survive. Female cuckoo bees do not collect pollen for their young, but because they visit pollen-producing flowers to find nectar for themselves they are nevertheless considered pollinators, spreading pollen between flowers.

We have two species of cuckoo bumble bees in Squamish. One is the indiscriminate cuckoo bumble bee (Bombus insularis) which is known to prey on the yellow-fronted bumble bee (Bombus flavifrons), one of our four common bumble bee species . The other is the yellowish cuckoo bumble bee (Bombus flavidus): for these we have no direct records to indicate which of our local bumble bee species serve as hosts. However, our common species are all possibilities because they belong to the subgenus Pyrobombus, which records from Europe show as a host group. The yellowish cuckoo bumble bee is, in my experience, much more common here, and that makes sense to me if there are so many more possible nests maintained by host species.

Other bees have their own genera of cuckoo bees, within the same bee family. We have at least four other examples of these relationships reported in iNaturalist for Squamish.

• We had a great example in spring 2024 of nesting mining bees (genus Andrena) with their cleptoparasitic nomad bees (genus Nomada) waiting outside nest holes. When the female Andrena left the nest to collect pollen, a waiting female Nomada could enter to lay an egg. Nomada can often be seen where Andrena are nesting.
• Our leafcutter bees (genus Megachile) are preyed upon by sharp-tail bees (genus Coelioxys ). One local species can be identified because of its red legs, but most that are seen here can’t be identified to species from photographs. Both the Megachile and Coelioxys bees are common in Squamish.
• Some of the sweat bee family (Halictidae) are preyed upon by  blood bees (genus Sphecodes). These bees are quite large and have a distinctive bright red abdomen. They are relatively common in Squamish and are known to prey on many species that occur locally.
• The least common example I know of a bee host-prey relationship here is that of the cellophane bee (genus Colletes). It is host to the Olympia cellophane-cuckoo bee (Epeolus olympiellus), only found in the Pacific North West, and almost always at the coast.

Here is a gallery of our local cuckoo bees with some of their host bees.

Some cuckoo bees are considered at risk. Their survival depends completely on the success of their host species. It may seem strange, but, from a biodiversity perspective, it is important that the cuckoo species as well as the host species are able to thrive.

Gwen

Banner photo: Male red-footed cuckoo leafcutter bee (Coelioxys rufitarsis), a cuckoo species that preys on our leafcutter bees (Megachile).