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Excerpted with permission fromA Sting in the Tale: My Adventures with Bumblebees, by Dave Goulson. Available from Picador.Originally published in Great Britain by Jonathan Cape, a division of Random House Group, Ltd.Copyright © 2014.
Let us travel back in time 135 million years. The vast supercontinent of Gondwana was beginning to break up, with South America drifting off to the west of Africa, and Australia moving majestically off to the east. Antarctica decided to head south, dooming all but the most adaptable of its inhabitants to an eventual icy grave. The South Atlantic and Indian Oceans were slowly forming.
At this ancient time, an era known to geologists as the Cretaceous, the continents were clothed in green forests of tree ferns, cycads, huge horsetails, and conifers such as pines and cedars. This was the height of the reign of the dinosaurs, although not the species that are so well known to schoolchildren the world over: amongst the trees, herds of vast herbivores such as Iguanodon grazed, standing on their hind legs to reach higher foliage; heavily armoured, tank-like species such as Gastonia bulldozed through the undergrowth; and packs of ferocious meat-eaters such as Utahraptor hunted their prey. The air swarmed with primitive insects including oversized dragonflies and early butterflies, and this was also the heyday of the pterosaurs, the largest animals ever to fly above the earth, with wingspans up to 12 metres. Much smaller dinosaurs had also taken to the air; feathers, probably first evolved to help these little creatures keep warm, became elongated on their forelegs to allow gliding and, eventually, active flight. These were the first birds. Our own ancestors at this time were rather unimpressively small, rat-like creatures skulking in the undergrowth, nervously coming out at night to nibble on insects, seeds and fallen fruit. If we could travel to this ancient land, we might be too concerned with the dangers posed by the larger wildlife to notice that there were no flowers; no orchids, buttercups or daisies, no cherry blossoms, no foxgloves in the wooded glades. And no matter how hard we listened, we would not hear the distinctive drone of bees. But all that was about to change.
Sex has always been difficult for plants, because they cannot move. If one cannot move, then finding a suitable partner and exchanging sex cells with them poses something of an obstacle. The plant equivalent of sperm is pollen, and the challenge facing a plant is how to get its pollen to the female reproductive parts of another plant; not easy if one is rooted to the ground. The early solution, and one still used by some plants to this day, is to use the wind. One hundred and thirty-five million years ago almost all plants scattered their pollen on the wind and hoped against hope that a tiny proportion of it would, by chance, land on a female flower. This is, as you might imagine, a very inefficient and wasteful system, with perhaps 99.99 per cent of the pollen going to waste – falling on the ground or blowing out to sea. As a result they had to produce an awful lot.
Nature abhors waste, and it was only a matter of time before the blind stumbling of evolution arrived at a better solution in the form of insects. Pollen is very nutritious. Some winged insects now began to feed upon it and before long some became specialists in eating pollen. Flying from plant to plant in search of their food, these insects accidentally carried pollen grains upon their bodies, trapped amongst hairs or in the joints between their segments. When the occasional pollen grain fell off the insect on to the female parts of a flower, that flower was pollinated, and so insects became the first pollinators, sex facilitators for plants. A mutualistic relationship had begun which was to change the appearance of the earth. Although much of the pollen was consumed by the insects, this was still a vast improvement for the plants compared to scattering their pollen to the wind.
To start with, insects had to seek out the unimpressive brown or green flowers amongst the surrounding foliage. It was now to the advantage of plants to advertise the location of their flowers, so that they could be more quickly found and to attract insects away from their competitors. So began the longest marketing campaign in history, with the early water lilies and magnolias the first plants to evolve petals, conspicuously white against the forests of green. The first pollinators may have been beetles, which many water lilies still rely on to this day. With this new reliable means of pollination, insect-pollinated plants became enormously successful and diversified. Different plants now began vying with one another for insect attention, evolving bright colours, patterns and elaborate shapes, and the land became clothed in flowers. In this battle to attract pollinators, some flowers evolved an additional weapon – they began producing sugar-rich nectar as an extra reward. As these plants proliferated, so the opportunities for insects to specialise grew, and butterflies and some flies evolved long, tubular mouthparts with which to suck up nectar. The most specialised and successful group to emerge were the bees, the masters of gathering nectar and pollen to this day.
All bees feed more or less exclusively on nectar and pollen throughout their lives. While many other insects such as butterflies and hoverflies feed on flowers as adults, very few do so as young too. Flowers are sparsely distributed in the environment, and immature insects cannot fly from one to another as only adult insects have wings. The innovation unique to bees is that the adult females gather the food for their offspring, so that their larvae do not need to move at all. The larval stage is maggot-like, legless and generally rather feeble, being defenceless and capable of only very limited movement. They are entirely dependent on the food provided by the adult bees.
The first bees evolved from wasps, which were and remain predators today. The word ‘wasp’ conjures up an image of the yellow-and-black insects that often build large nests in lofts and garden sheds and which can be exceedingly annoying in late summer when their booming populations and declining food supplies force them into houses and on to our picnic tables. Actually, there are enormous numbers of wasp species, most of whom are nothing like this. A great many are parasitoids, with a gruesome lifestyle from which the sci-fi film Alien surely took its inspiration. The female of these wasps lays her eggs inside other insects, injecting them through a sharply pointed egg-laying tube. Once hatched, the grubs consume their hosts from the inside out, eventually bursting out of the dying bodies to form their pupae. Other wasp species catch prey and feed them to their grubs in small nests, and it is from one such wasp family, the Sphecidae, that bees evolved. In the Sphecidae the female wasps stock a nest, usually an underground burrow, with the corpses, or the paralysed but still living bodies, of their preferred prey. They attack a broad range of insects and spiders, with different wasp species preferring aphids, grasshoppers or beetles. At some point a species of sphecid wasp experimented with stocking its nest with pollen instead of dead insects. This could have been a gradual process, with the wasp initially adding just a little pollen to the nest provisions. As pollen is rich in protein, it would have provided a good nutritional supplement, particularly at times when prey was scarce. When the wasp eventually evolved to feed its offspring purely on pollen, it had become the first bee.
Exactly how long ago this happened we do not know for insects rarely form fossils, and so we have to piece together their history from parse information. Occasionally, insects become trapped in tree resin which fossilises to amber, beautifully preserving them for eternity. Crawling insects such as ants seem to have become trapped most often, but it seems that bees were rarely so foolish and examples of bee fossils are particularly few. The oldest known bee in amber is about 80 million years old, and is of a type known as a stingless bee, similar to species that live today in South America. These are advanced social bees that live in vast colonies, so it is a pretty good guess that the earliest bees were on the wing long before this.
A rather different source of information on the evolution of insects is provided by analysis of DNA sequences, which allow us to make educated guesses as to how long ago different evolutionary lineages diverged. Studies of the similarity of the DNA in wasps and bees suggest that the first bees appeared about 130 million years ago, 50 million years before the first known fossil bee, and probably very shortly after the first flowers evolved in the Cretaceous.
Over the millennia, bees have adapted to feeding on flowers in various ways. Many species have become hairy, which helps them to brush pollen from flowers, and also to hold it in flight. In the leafcutter bees, for instance, the pollen is stored among dense hairs on the underside of the abdomen, so that the bees often appear to have bright yellow bellies. In bumblebees and honeybees, stiff bristles on the hind legs form a basket into which pollen is placed. If one is going to visit flowers for their pollen it makes sense to also collect their nectar, for this is a great source of sugar to sustain flight. Nectar is expensive for plants to produce, and therefore many flowers evolved over time to hide their nectar, ensuring that only the insects most likely to provide them with a reliable pollen delivery service can reach it. Many bees evolved longer and longer tongues to make it easier for them to reach nectar hidden within flowers; some now have tongues longer than their bodies.*
The earliest bees, 130 million years ago, were almost certainly solitary species, and the majority of present-day bee species remain so. Each female builds her own nest, usually in a small hole in the ground, or in a tree or wall. In the leafcutter bees, the nest is lined with neatly snipped semicircles of leaves, glued together with silk. Once the nest is complete, the female bee fills it with pollen mixed with nectar and lays one or more eggs. The life cycles are very variable, but usually the female does not care further for her offspring, simply sealing up the nest entrance and leaving them to eat their pollen and develop on their own. Most solitary bees in temperate climates have just one generation a year, so the offspring will sometimes spend eleven months developing in the nest before emerging as adults.
Solitary bee species tend to be small, dark or drably coloured, which is why people seldom notice them. Nonetheless many are quite common and often live in gardens, some even nesting in the old mortar between the bricks of our houses. Only rarely do the lives of these inconspicuous creatures impinge noticeably on our own, although they probably contribute substantially to pollination of many crops without us being aware of it (honeybees often get all the credit).
I was once involved in a rather strange and less welcome instance of a solitary bee impacting on humans. I received a call from aeronautical engineers who were investigating the cause of an instrument failure which had forced a military helicopter belonging to a certain well-known superpower – confidentiality agreements prevent me from revealing which one – to perform an emergency landing. A small but vital instrument, which measures airspeed and controls the speed of rotation of the rear rotor had failed, and the British manufacturers of the instrument found themselves under suspicion of supplying dangerously defective components. Upon close examination, it transpired that the cause of the fault was a plug of a sticky yellow substance blocking a tiny but necessary hole in the instrument casing. Their investigations suggested that the substance might be pollen, which was when I was brought in. It was indeed pollen, identifiable as belonging to some species of legume, no doubt placed there by a small solitary bee which had adopted the hole as its nest while the aircraft was parked. When it returned from a foraging trip, the bee was presumably rather disappointed to find that its nest had vanished.
Let us return to our journey through time. To recap, bees first appeared perhaps 130 million years ago, and by 80 million years ago some had evolved a social lifestyle, for the earliest fossil is of a social stingless bee. Some 65 million years after the first bees appeared (and, coincidentally, 65 million years before the present), the earth went through a catastrophic change. Most scientists these days agree that a meteor struck the earth roughly where the Yucatan Peninsula now lies, causing tidal waves and massive volcanic eruptions which filled the air with so much dust that it blocked out the sunlight, in turn causing temperatures to fall below freezing for months or years on end. Almost all large forms of life on earth then died out very swiftly, the dinosaurs among them. Amazingly, representatives of many of the smaller groups of organisms survived somehow. So far as the sparse fossil record reveals, the main insect groups – bees, ants, grasshoppers, beetles and so on – seem to have recovered swiftly, although it is likely that countless individual insect species became extinct. The flowering plants also survived, presumably as dormant seeds. Our own ancestors – small, furry and warm-blooded – may have kept themselves alive by feeding on the corpses of larger animals or on stores of seeds and nuts, and perhaps by keeping warm in the vast drifts of rotting vegetation that resulted from the forests’ death. Before long the earth was once again teeming with life, albeit with rather smaller forms.
Our mammalian ancestors took advantage of the many unoccupied niches and diversified. Were it not for the meteor, it is doubtful if most of the larger mammals – including ourselves – would ever have appeared. Some species grew much larger, filling the roles once occupied by dinosaurs; these included ground sloths that stood 6 metres tall and weighed 3 tonnes, and the vast rhinoceros-like Uintatherium. It was into this world of giants that the first bumblebees appeared, about 30 to 40 million years ago. This corresponded with a period of cooler temperatures, which may have encouraged bees to become larger and furrier. Our best guess is that the first bumblebee lived somewhere in the mountains of central Asia, since this is still the area of greatest bumblebee diversity. From here they spread west, east and north from the Himalayas to occupy Europe, China and Siberia, and even up into the Arctic Circle. As bumblebees overheat in warm climates, they did not spread far southwards towards the equator, which is why until some recent deliberate introductions there were no bumblebees in Australia, New Zealand or Africa south of the Sahara. About 20 million years ago bumblebees crossed from Siberia to North America, where they thrived and spread southwards. Eventually about 4 million years ago a handful of species moved down through the mountain chains of Central America to occupy South America, becoming the only naturally occurring bumblebees in the southern hemisphere.
So now we arrive at the present day. The world is blessed with an extraordinary diversity of species of organism. About 1.4 million have been named so far, but estimates as to the true total vary hugely from 2 million to 100 million. Two hundred and fifty of the known species are bumblebees (members of the genus Bombus, of which twenty seven occur naturally in the UK). There may be a few more yet to be found in remote regions, but probably not many. There are about 25,000 known species of bee (superfamily Apoidea, with 253 known from the UK), but many more undoubtedly remain to be discovered, particularly in the tropical regions. Bees in turn belong to the immensely successful insect order the Hymenoptera, which also includes ants and the wasps from which bees evolved, of which there are 115,000 known species. The Hymenoptera in turn are just one of many types of insect, collectively the most successful group of organisms on earth, with about 1 million named species, or about 70 per cent of all known species on earth.
Until recently, this number of species was the highest it had ever been since life began. However, in the last few thousand years it has started to drop rapidly as man has remoulded the surface of the planet. As our ancestors spread out from Africa, many of the large mammals such as mammoths, giant sloths and sabretoothed tigers swiftly disappeared, either hunted to extinction by man or driven to extinction because their prey disappeared. Most would have had no defence against groups of men hunting with spears and bows and arrows. At present, species are going extinct at somewhere between 100 and 1,000 times the natural rate, largely driven by habitat destruction and the ravages wrought by invasive species. It is estimated that one species goes extinct every twenty minutes.
So far, only three bumblebees are thought to have gone extinct globally: Bombus rubriventris,Bombus melanopoda and Bombus franklini, but surely more will follow. It is the threat of extinction of large mammals such as tigers or rhinoceros that tends to capture the public’s attention, but arguably it is the loss of the smaller creatures that should give us most concern. Insects are responsible for delivering numerous ‘ecosystem services’ such as pollination and decomposition, and there is no doubt that little life on earth (including ourselves) could survive without them. As the famous biologist E. O. Wilson said, ‘If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed ten thousand years ago. If insects were to vanish, the environment would collapse into chaos.’
* The record holder is not a bee, but a hawkmoth, Xanthopan morganii, which has a tongue of about 30 centimetres long (the moth itself being 6 centimetres long). This moth feeds upon the Madagascar star orchid Angraecum sesquipedale, in which nectar is hidden at the base of spurs 30 centimetres deep, in a beautiful example of co-evolution. Upon being sent examples of the orchid in 1862, Charles Darwin predicted that there must exist a moth with a tongue long enough to feed upon it, but it was not until 1903 that the moth was finally discovered.