BBC Wildlife Magazine
The bee: 120 million years in the making
From the colossal to the neon-coloured, discover how some of the most important pollinators on the planet earnt their stripes. 120 MILLION YEARS IN THE MAKING
From UK garden regulars to exotic species found around the world, learn more about the evolution of bees
Bees are in trouble. From pesticides and parasites to colony collapse disorder and dwindling habitat, the challenges they face have caused widespread declines in honeybees and wild species alike. But after years of reading such headlines, we find ourselves in the odd position of being more familiar with the plight of bees than we are with the bees themselves. What do we really know of their history, their biology and their habits? To address such deficits, the best place to start is with the most basic question of all: what is a bee? Luckily, there is an answer to that query that is both memorable and simple, and that really does sum up the major steps in bee evolution – a bee is a hippy wasp.
The first thing to remember is that wasps came first. They’d been happily buzzing around the planet for millions of years before bees came along. Bees evolved from the wasps and they still look a lot like them, which is why the two groups are so often confused. But if you are being harassed at a picnic, and you see your attackers swarming around the sausage rolls and stealing chicken from the sandwiches, then don’t blame bees. Your assailants are most certainly wasps, because wasps are hunters and scavengers, constantly scouring the landscape for flies, caterpillars, spiders or scraps of fleshy protein to take back to the nest and feed to their larvae. Bees, on the other hand, won’t do more than nip a bit of berry jam or steal a sweet sip from your soda. That’s because the key innovation that started them on their own evolutionary pathway was dietary. They gave up eating meat, and instead began provisioning themselves and their babies solely from the products of flowers.
The details of this transition remain murky, because the fossil record is poor. But it’s likely that early proto-bees targeted flowers as a good place to hunt other insects, and began eating pollen and nectar inadvertently on the bodies of their prey. Once the switch was complete, however, it offered all sorts of advantages. Gathering harmless pollen is a far safer way to get a meal than, say, attacking a fearsome spider. Soon, the behaviours and bodies of bees began to adapt to this new lifestyle.
Bees have been with us for at least 120 million years, since the middle of the Cretaceous Period.
They developed long, tube-like tongues for sipping nectar from deep flowers, as well as feathery, branched hairs specifically adapted for carrying pollen back home to the nest. The sensory organs on their antennae became attuned to floral scents, and they became experts in navigation, plotting and memorising efficient routes from blossoms to nest and back again.
Of course, there is nuance to the story. Some bees have become parasitic and no longer bother collecting pollen at all, and a few tropical species have even returned to carnivory. But for the basics of bee evolution, just remember that they are the long-haired, flower-loving vegetarians. The hippy wasps.
All of this evolutionary activity took place a long time ago. Bees have been with us for at least 120 million years, since the middle of the Cretaceous Period. Time travellers visiting that era might first notice the dominance of dinosaurs, but there was an equally dramatic story playing out in the vegetation below those lumbering feet. Ferns and cycads abounded, but where were the flowers? Any blossoms on offer were tiny and hard to find, bit players in flora still dominated by things such as ginkgos and early conifers. It was hardly a promising landscape for the evolution of insects that relied solely on pollen and nectar, which means that the first bees were making a rather bold bet. But the wager paid off handsomely, for bees and flowers alike.
Recent estimates put the number of different bees in the world at more than 20,000 species.
To early naturalists sorting through the fossil record, the sudden rise of flowering plants during the latter part of the Cretaceous was long considered inexplicable. No flowers appeared anywhere in layer after layer of ancient life, and then all at once they were abundant and they were diverse. Charles Darwin famously called it an “abominable mystery,” and considered it a serious challenge to his concept of evolution as a slow process of incremental change. Rarely noted, however, is that in the same letter where Darwin made his oftenquoted ‘mystery’ comment, he mentioned his correspondence with a lesser-known naturalist of the day, a Frenchman named Gaston de Saporta. In de Saporta’s view, flowering plants had indeed evolved rapidly, directly as a result of their interactions with flower-visiting insects, such as bees. He theorised that insect pollinators vastly increased the rate of intercrossing among flowers, leading quickly to more species.
Darwin didn’t believe it. He preferred to think that flowering plants must have evolved slowly somewhere else, and then dispersed rapidly to the places where they became fossilised. Darwin’s idea involved a hypothetical continent somewhere in the Southern Hemisphere, where flowers could have developed in isolation, though even he admitted that was “a wretchedly poor conjecture”.
Still, the evolutionary importance of insects remained obscure until a rash of pollination studies in the late-19th century showed that de Saporta had been right all along. Most of that research involved bees – how they not only promoted out-crossing, as de Saporta had suspected, but how plants competed and diversified in an effort to woo their buzzing visitors.
Flower traits as fundamental as colour, shape and fragrance often boil down to the proclivities of bees, and catering to that evolutionary pressure helped flowering plants expand to dominate over 90 per cent of the Earth’s terrestrial flora. The results can be seen everywhere from mountain meadows to rainforest canopies to the window display at the nearest flower shop. But what is less well known is how the rapid diversification of flowering plants led, in turn, to an incredible diversity of bees.
Recent taxonomic estimates put the number of different bees in the world at more than 20,000 species, more than all the mammals and birds combined. This figure surprises many people, because
when we think of bees our minds turn immediately to the one species we know best – the honeybee. Domesticated for at least 4,000 years, this native of Africa and the Mediterranean basin now lives nearly everywhere that people do, providing honey, wax and vital crop pollination. But while we marvel at their social order and teeming hives, honeybees are an oddity.
Rather than massing by the thousands around a single queen, the vast majority of bees are loners. They inherited that solitary habit from their ancestors, and most found no evolutionary reason to change their ways. In fact, living alone may be the key to their great diversity.
For social species, such as honeybees (or that other familiar clan, the bumblebees), providing for a large colony requires a flexible diet. They need to visit a wide range of flowers – nearly whatever is blooming – just to keep up with a hungry and growing hive. Solitary bees, on the other hand, can afford to specialise. After mating in the spring, each female sets off to provision her own tiny nest. She may live only a matter of weeks, tucking away enough pollen and nectar for a handful of offspring that will emerge the following season to start the whole cycle over again. This simple lifestyle lends itself to endless variation, with species becoming specially adapted to particular flower types, time periods, nesting habitats and foraging strategies.
Mining bees, for example, are often food specialists. They nest in the ground and time their emergence to focus on the blooms of their chosen plants. Small and darkcoloured, the most distinctive feature of any given miner is often what it eats. Many species are active in the spring, feeding on their own narrow selection of plants, such as willows, heaths, evening primroses or mustards.
Others dig their way out in the autumn, to take advantage of lateblooming asters.
Members of the oil-collecting bee family are even pickier. As their name implies, they supplement the pollen in their diet with droplets of floral oils, which also come in handy for waterproofing their nests. This quirk restricts them to the few plants with
The world’s largest bee lives only inside the nests of rainforest termites in Indonesia.
oil-producing glands on their petals. In South Africa, co-evolution with twinspur flowers has led to oil-collectors with front legs twice the length of their bodies – awkward for walking, but perfectly suited to scraping their favourite meal from the deep tubes of their preferred blossoms.
Home sweet home
Varied nesting opportunities have also helped spur the diversity of bees. Since mating often occurs precisely when and where they emerge from their winter sleep, exploiting different nest sites can quickly lead to the kind of reproductive isolation necessary for making new species.
Like mining bees, many sweat bees and masked bees dig tunnels for their nests, adapting to conditions that range from cliff faces to sand dunes to hard-packed earth.