Cuckoo bees: cheats of the bee world

Raising baby bees is hard work. Some species have found another way.

The world's most famous cuckoos are feathered ones. Europe's common cuckoo (Cuculus canorus) in particular has long fascinated naturalists, with Aristotle marvelling at the cuckoo's cruel and unusual reproductive habits as far back as 350 B.C. Cuckoos are "brood parasites". They do not build their own nests, nor care for their own young. Instead, they lay their eggs in the nests of other birds, often ones much smaller than themselves. The young cuckoo hatches first and ejects the other eggs or chicks. The diligent host parents then rear the young cuckoo as though it was their own, continuing to feed it even as it grows monstrously larger than themselves. Cuckoos are thus professional cheats, offloading onto other species the burden of feeding and protecting their offspring.

While avian cuckoos may be the most famous, they aren't the only ones. Australia is home to several species of cuckoo bees. Like their avian namesakes, these bees are obligate parasites of the hard work of other bees. They also include some of Australia's most strikingly beautiful native bees. For example, the neon cuckoo bee (Thyreus nitidulus) - pictured above - lays its eggs in the nests of blue-banded bees (Amegilla cingulata) - pictured below.

Blue-banded bees are common residents of many Australian cities. Their noisy buzzing makes them easy to spot at flowers, and males can often be seen roosting at night in groups during warmer months, their mandibles locked onto a twig. Female blue-banded bees meanwhile spend the spring busily making nests—tunnels that they dig into clay or dirt slopes or walls. At the end of the tunnel they build brood cells and provision each with a ball of pollen-rich food. Once finished, they lay an egg and seal the cell. When the egg hatches, the larva munches through the stored food, pupates in the safety of the nest and eventually emerges as an adult.

Cuckoo bees upset this process by sneaking into nests and inserting their own egg into the brood cell. The cuckoo bee's egg develops quickly and hatches first, eating up all the food and leaving the cell's legitimate resident to starve.

And neon cuckoo bees aren't the only ones. The domino cuckoo bee (Thyreus lugubris) parasitises the nests of teddy bear bees (Amegilla bombiformis). Coelioxys cuckoo bees lay their eggs in the nests of leafcutter bees (Megachile sp.). And some of the social nesting reed bees (e.g. Exoneura robusta) are infiltrated by brood parasites that lay eggs in the nest but don't contribute any work. There are likely others among the Australian bee fauna, as yet undiscovered. It seems that wherever hard work is found in nature, natural selection will also favour some cheaters.

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