Cuckoos are not the only animal to have their young raised by other species. Bees, wasps, and fish also exhibit the same parasitic behaviour.
It’s a smart (and selfish) evolutionary move to put your eggs into another bird’s nest. They do all the work, you get the benefit. Roaming bees (Nomada) seek out nests that are rich with pollen and empty of other parasitic bees, fly on in, lay their eggs, and then leave. When the larvae hatch they eat the host’s eggs and all the pollen and nectar collected for them.
While this is a bit disturbing, the cuckoo bees have nothing on the cuckoo catfish. This fish is native to Lake Tanganyika, which stretches across Tanzania, Burundi, Zambia, and the Democratic Republic of the Congo. (Side-note: this lake is the second-oldest, second-deepest, and second-largest freshwater lake in the world.)
Several of the other fish species in Lake Tanganyika raise their children inside their mouths – the technical term is “mouthbrooding.” The cuckoo catfish sneaks into these species’ mouths and lay their own eggs. IN THEIR MOUTHS. Just like the bees’ larvae, the little fish hatch first and then eat all of the host species’ own eggs. STILL IN THEIR MOUTHS.