Don’t judge the kleptoparasitic bee; she’s just doing what she’s programmed to do.
But a quick glance at the first part of her name—”klepto”—gives you a sense of this insect’s style. Yep, she’s basically a thief.
Let’s look at the big picture. The female kleptoparasitic bee (a.k.a. cuckoo bee because of behaviors similar to the cuckoo bird’s, along with many other critters) can’t build her own nest because she doesn’t have the pollen-collecting hairs (“scopa”) that most female bees have. So, when she’s ready to lay her eggs, the cuckoo bee simply sneaks into the nest of a busy pollen-collecting mother at an opportune moment and lays her egg on top of her host’s egg.
So far, these hijinks resemble those of the cuckoo—mother bird lays her eggs in another bird’s nest, sometimes leaving everything intact, sometimes removing an egg or two that belong to her host. She may occasionally try to compel the host into raising her babies for her. Nothing to be proud of, but it’s not too terrible.
Such kleptoparasitism is seen elsewhere in nature too. A chinstrap penguin may wander away with some rocks from a fellow penguin’s nest, for example, or a gull may swoop in to steal the fish a diving bird just caught. When this type of parasitic behavior is found within one species (like the penguin) it’s called “intraspecific.” When it involves different species, it’s “interspecific,” as is most often the bees’ case. But what’s interesting is that in the latter instance, the species are not very different—in fact, they often look alike.
It’s called Emery’s Rule. To understand it, think of Aunt Sally “borrowing” a lipstick from your mother’s medicine cabinet. Carlo Emery was an entomologist in the 1920s who noticed that social parasites in the insect world (as well as fungi and mistletoe) often tended to be from closely related species and resemble their hosts in size and appearance.
But though the cuckoo bee is closely related to some of her hosts, she’s not exactly kind to them in the end. In the host’s nest, the cuckoo-bee egg develops rapidly and hatches out a ravenous little one with notably large mandibles. The young bee uses these to eat the pollen the host has painstakingly collected, bite into the host’s egg to suck out the yolk, or eat the host larvae. The mother cuckoo bee might lay more eggs and kill the host queen in order to take her place.
Kind of makes the penguins and Aunt Sally look like saints.