by Jaime Pawelek and Rollin Coville
The cuckoo habit has evolved independently in many groups of bees and for entomologists it’s interesting from a phylogenetic and ecological aspect. Cuckoo bees are similar to cuckoo birds that practice brood parasitism, like the brown-headed cowbird. Parasitism is when one creature forms a relationship with another type of creature and benefits positively, while the other does not. For example, cowbirds lay their eggs in the nests of other birds (brood parasitism) and when they hatch the other bird raises the cuckoo bird like it’s their own young. The cowbird is usually larger than the bird it parasitizes and therefore may outcompete the other baby birds. With cuckoo bees though, the cuckoo bee lays its egg in another bee’s nest and their egg hatches early, and the cuckoo larvae eats the other bee’s provisions. The female cuckoo bee sometimes kills the other bee’s egg or she leaves it for her larvae to eat. Cuckoo bee larvae often have larger mandibles that they use to chomp and kill the other larvae.
Cuckoo bees often do not look like “classic” bees in that they don’t have much hair on them, and for this reason they may be confused with wasps. Cuckoo bees don’t have to collect pollen and nectar for their young any longer, so they don’t have any pollen collecting hairs on their bodies. They do visit flowers for nectar because it provides them with the energy they need for daily activities, like looking for other bee nests to parasitize. This adaptation begs the question, “are cuckoo bees pollinators?” This is something we are currently researching in our lab. While visiting flowers, cuckoo bees will have some pollen that sticks to them through electrostatic attraction, but we have not investigated whether or not they are successful at pollinating flowers.
Most cuckoo bees parasitize nests of just a few bee species (2-5), but some are very specific and only parasitize nests of just one other bee species. Most female bees spend their day visiting flowers and collecting pollen and nectar to provision their nest with. A cuckoo bee female spends her day differently. She searches for nests by flying low over the ground and only visits flowers for nectar when in need of energy. The cuckoo bee will wait outside the host nest and wait for the female to leave. It then jumps at the chance to enter the empty nest and lay its’ own egg. Cuckoo bees actually represent a higher percentage of bees than one might think, possibly 15% of the worlds’ bees.
In our garden in Berkeley, CA we have seen this parasitic relationship take place. We have cuckoo bees, Coelioxys rufitarsis, which parasitize the nests of a common leafcutting bee, Megachile perihirta. The female Coelioxys rufitarsis flies low over the ground in search of a nest of Megachile perihirta, then waits outside for her to leave so she can enter and lay her own egg inside. If you are a careful observer you may even see this taking place. Seeing this relationship in our garden is encouraging because it means that a food web is developing and interspecies relationships are becoming more complex.