What, Exactly, is a Bee?
In essence, a bee is a glamorous wasp. This is not to say that there is anything unglamorous about wasps, but most people draw a sharp distinction between those seemingly friendly, apparently joyous little creatures that go about visiting hollyhocks on summer days, and those ferocious and sometimes threatening denizens of the soda can, the eaves of the house, the sand dunes back behind the swimming beach. Bees are a particular lineage of wasps, composed of several distinctive families, all sharing a common ancestor. This branch on the tree of life fits within a larger bush, a lineage called the superfamily Apoidea. The Apoidea includes predatory wasps as well as bees, and its members share so many distinctive characteristics as to indicate that this bush is simply one branch within a much larger bush called the suborder Apocrita, which, in turn, fits within the insect order hymenoptera, et cetera. The branch that includes bees is sometimes called the Anthophila, latin for “flower lover.” As a branch, the Anthophila have done very well for themselves. The nine families of bees include approximately 30,000 species, outnumbering their various distant relatives that still carry on a predatory lifestyle.
These predators, called Sphecid wasps, include about 8000 species worldwide. They are still out there, making a living much way the Mesozoic ancestors of the bees probably did. Sphecids are ferocious creatures, hunting spiders, grasshoppers, and other unfortunate arthropods. They are very diverse their methods of doing this, but a clear pattern of simple to complex in their evolution. The rapacious habits of sphecid wasps are all variations on a single theme. They go out and find a victim. They sting it into a state of paralysis. They drag it home to a nest. They lay an egg on it. The larva hatches, devours the victims, and reaches adulthood. This new adult goes out to kill and kill again, just like its mother, or to mate and die, just like its father. The nest may either be previously constructed, constructed on the spot, or the result of an opportunistic decision to use whatever crevice is nearby when the mother wasp dispatches her unfortunate victim. This nest may be excavated in the soil, chewed into a rotting log, carefully crafted out of mud, resin, or something resembling silk. Within this nest, there are cells; particular enclosed chambers where the unfortunate victims of sphecid maternal instinct wait, in isolation, for the growing wasp larva to consume them alive. A nest may have a single cell, or many. A cell may have a single prey item, or many. These victims may all be members of the same species, or members of an assemblage of arthropods that, to the mother wasp, looked sufficiently similar to warrant killing. No matter what the contents of the call, an egg is laid within, either before or after it is stocked with tortured victims, and that egg is intended to hatch and ultimately devour the contents. Typically, the focus of sphecid hunting is very narrow. The mother wasp will focus obsessively on hunting a particular type of prey, such as spiders of the genus Neoscona. Different wasps hunt different victims, though there is a tendency for particular lineages of sphecids to focus on a particular kind of prey. Members of the family Ampulcidae, for instance, terrorize cockroaches. Members of the genus Ammophila, for instance, hunt crickets.
This hunting behavior serves one purpose, to ensure that the developing offspring of a wasp have enough to eat. Adult sphecids wasps do not actually eat the creatures they kill. Like many flies, beetles, vespid wasps, Lepidoptera, and bees also, sphecid wasps have a very distinct dietary dichotomy between adults and offspring. Adults drink nectar from flowers. Nectar is basically all sugar and no protein. Carbohydrates are an excellent source of energy. The lack of protein is nearly irrelevant, because the animal has stopped growing, and nectar is sufficient to keep the animal going as long as it hunts victims and digs nests. This nectar feeding habit might actually be even older than the prey-hunting habits of the sphecidae, an evolutionary holdover from some primitive hymenopteran ancestor that drank sap from sap flows as a supplementary energy source.
The common ancestor of the bees evolved a trait of enormous ecological significance, a trait which was to enable the diversification of bees into a tremendous number of species, and to influence the future evolution of almost every other plant and animal on land. It was right under the noses of the sphecid wasps as they drank nectar before their next foraging run-pollen. Rather than hunting unfortunate insects as prey for their offspring, they evolved the ability to gather pollen, roll it into balls, soak it with nectar, and lay an egg on this mass. Animal material took the place of plant material in the cells of these new wasps. Basically, their life cycle stayed the same, though this switch in behavior precipitated the rapid evolution of various, diverse, structures and behaviors for pollen gathering. Pollen from some plants is stickier than pollen from other plants. Some plants have pollen that is much easier to reach. Suddenly, it became relevant which particular species of flowers these proto-bees were visiting. Some lineages of bees specialized on particular flowers, others did not.
Besides being less inherently ghastly, this provisioning behavior opens up a wide range of ecological possibilities. Pollen is a high-protein food full of nutrients, and when combined with nectar from flowers, it is ideal food for developing bee larvae. Unlike, say, a particular species of arboreal katydid, pollen is very abundant in the terrestrial environment, though pollen from a particular type of flower may not be. The insects their sphecid ancestors hunted, pollen from particular flowers is seasonally superabundant, but absent for most of the year. It is quite possible that the first bees inherited the ability to be dormant for long stretches of time, only emerging during the optimal window of time, from their sphecid ancestors. Not all bees do this, however. Some are present all year long, visiting a wide variety of flowers. Most importantly, however, this new specialization on pollen feeding exerted tremendous evolutionary pressure on the flowers the bees visited. An incidental effect of pollen feeding is the transfer of pollen, something of enormous consequence to the plants visited by bees.
Not all wasps that collect pollen are called bees. This remarkable shift in behavior and ecology has evolved at least twice. A second group of wasps, this time a lineage of vespoid wasps called the masaridae, has also evolved a pollen-gathering existing. Masarids resemble bees in many respects. For reasons that are unknown, perhaps simply because they were co-opted from many ecological niches because bees got to them first, the masaridae are not particularly species rich or ecologically important. Masarids are widely distributed in the tropics, but they are nowhere as important as bees in their ecological impact.
Likewise, not all bees gather pollen. Many have switched to an existence that is essentially parasitic upon other bees. This transition has happened many times in the evolution of bees, and it seems to occur whenever there is a clear opportunity for one species of bee to enter the nests of another species, usually a close relative, and to lay its own eggs in the cells built by another species. They are not like the usual parasites, flukes, tapeworms, ticks, and such, in that they rob parental care from their host, rather than nutrients, blood, glucose. Instead, they rob their host of parental care. In doing so, these villains of the bee world joined a long list of insect lineages that parasitize the cells off bees, and the pollen-collecting bees, the wasps.
Most people have a fairly clear idea of what a bee looks like. They are fuzzy or hairy, they are about the size of a honeybee, they are black and yellow, they have two pairs of wings, and they sting. Some people go even farther and tacitly assume that the only type of bee out there is the honeybee. If they stop to think about it farther, they add bumblebees to the list. This is not so much a reflection of a vast, aesthetic void on the part of the general public, much as the author tends to view it that way, as it is a reflection of exactly how efficiently bees go about their business without any need on our part to oversee their activities.
In fact, a honeybee is on the large size, as bees go. Bees occur in a range of sizes, from tiny members of the genus, Dialictus, which could easily fit on the head of a pin (maybe with their abdomen sticking out a bit), to very large carpenter bees of the genus Xylocopa, and queen Bombus, who would not be dwarfed by a golf ball if set right next to it. They come in a variety of stunning colors. Metallic blue and metallic green are favorite color schemes in the bee catalog, as are a range of silvery whites and greys, rusty reds and oranges, and amazing jet black, with or without red or yellow markings. Many bees are hairy, many bees are not. Hairs are thermoregulatory structures to bees, as well as pollen-gathering apparatus, and different species have evolved different levels of hairiness to accomplish an optimum thermoregulatory balance. Hair can be inconvenient under the soil, and in very tiny crevices as well, so there are a great many minimally hairy bees that, to a casual observer, resemble wasps. Bees are, in fact, quite diverse in their appearance.
Not all bees are social, in fact, most bees live solitary lives. Only a small fraction of bees live in colonies, and most social species live in colonies about the size of a football team or a metal band.
