refinement. The fertilised egg remains in the cone for one more year. Rich food supplies are laid down within its cells and waterproof coats are wrapped round it. Eventually, more than two years after fertilisation began, the cone dries and becomes woody. Its segments open, and out drop the fertilised fully provisioned eggs – seeds – which if necessary can wait for years before moisture penetrates them and stimulates them to spring to life.
By any standards, the conifers are a great success. Today, they constitute about a third of the forests of the world. The biggest living organism of any kind is a conifer, the giant redwood of California, which grows to 100 metres in height. Another conifer, the bristle-cone pine, which grows in the dry mountains of the southwestern United States, has one of the longest life-spans of any individual organism. The age of trees can easily be calculated if they grow in an environment where there are distinct seasons. In summer, when there is plenty of sunshine and moisture, they grow quickly and produce large wood cells; in winter, when growth is slow, the cells are smaller and the wood consequently more dense. This produces annual rings in the trunk. Counting those in the bristle-cone pine establishes that some of these gnarled and twisted trees germinated over five thousand years ago at a time when people in the Middle East were just beginning to invent writing, and the trees have remained alive throughout the entire duration of civilisation.
Conifers protect their trunks from mechanical damage and insect attack with a special gummy substance, resin. When it first flows from a wound it is runny, but the more liquid part of it, turpentine, quickly evaporates, leaving a sticky lump which seals the wound very effectively. It also, incidentally, acts as a trap. Any insect touching it becomes inextricably stuck and very often buried as more resin flows around it. Such lumps have proved to be the most perfect fossilising medium of all. They survive as pieces of amber and contain ancient insects in their translucent golden depths. When the amber is carefully sectioned, it is possible, through the microscope, to see mouthparts, scales and hairs with as much clarity as if the insect had become entangled in the resin only the day before. Scientists have even been able to distinguish tiny parasitic insects, mites, clinging to the legs of the bigger ones. Extracting the DNA from a blood-sucking arthropod seems likely to remain science fiction, however. Even attempts to do so from insects trapped in copal, the modern equivalent of amber only a few decades old, have all met with failure.
The oldest pieces of amber so far discovered date from around 230 million years ago, a long time after the conifers and the flying insects first appeared, but they contain a huge range of creatures, including representatives of all the major insect groups that we know today. Even in the earliest specimens, each type has already developed its own characteristic way of exploiting that major insect invention, flight.
Ancient bristlecone pine in winter, near Wheeler Peak in Great Basin National Park, Nevada, USA.
The dragonflies beat their two wings synchronously, with the front pair raised while the rear pair are lowered. This, however, creates very considerable physiological complexities. Their wings do not normally come into contact, but even so there are problems when the dragonfly executes sharp turns. Then the fore- and hindwings, bending under the additional stress of the turn, beat against one another, making an audible rattle that you can easily hear as you sit watching them make their circuits over a pond.
The later insect groups seem to have found that flight was more efficiently achieved with just one pair of beating membranes. Bees and wasps, flying ants and sawflies all hitch their fore- and hindwings together with hooks to make, in effect, a single surface. Butterfly wings overlap. Hawkmoths, which are among the swiftest insect flyers, capable of speeds of 50 kph, have reduced their hindwings very considerably in size and latched them on to the long narrow forewings with a curved bristle. Beetles use their forewings for a different purpose altogether. These creatures are the heavy armoured tanks of the insect world and they spend a great deal of their time on the ground, barging their way through the vegetable litter, scrabbling in the soil or gnawing into wood. Such activities could easily damage delicate wings. The beetles protect theirs by turning the front pair into stiff thick covers which fit neatly over the top of the abdomen. The wings are stowed beneath, carefully and ingeniously folded. The wing veins have sprung joints in them. When the wing covers are lifted, the joints unlock and the wings spring open. As the beetle lumbers into the air, the stiff wing covers are usually held out to the side, a posture that inevitably hampers efficient flight. Flower beetles, however, have managed to deal with this problem. They have notches at the sides of the wing covers near the hinges so that the covers can be replaced over the abdomen, leaving the wings extended and beating.
The most accomplished aeronauts of all are the flies. They use only their forewings for flight. The hindwings are reduced to tiny knobs. All flies possess these little structures but they are particularly noticeable in the crane flies, the daddy-long-legs, in which the knobs are placed on the ends of stalks so that they look like the heads of drumsticks. When the fly is in the air, these organs which are jointed to the thorax in the same way as wings, oscillate up and down a hundred or more times a second. They act partly as stabilisers, like gyroscopes, and partly as sense organs presumably telling the fly of the attitude of its body in the air and the direction in which it is moving. Information about its speed comes from its antennae, which vibrate as the air flows over them.
Flies are capable of beating their wings at speeds up to an astonishing 1,000 beats a second. Some flies no longer use muscles directly attached to the bases of the wings. Instead they vibrate the whole thorax, a cylinder constructed of strong pliable chitin, making it click in and out like a bulging metal tin. The thorax is coupled to the wings by an ingenious structure at the wing base, and its contractions cause them to beat up and down.
Longhorn beetle (Cerambycidae) in flight Rookery Wood, Sussex, England, UK, July.
The insects were the first creatures to colonise the air, and for over a 100 million years it was theirs alone. But their lives were not without hazards. Their ancient adversaries, the spiders, never developed wings, but they did not allow their insect prey to escape totally. They set traps of silk across the flyways between the branches and so continued to take toll of the insect population.
Plants now began to turn the flying skills of the insects to their own advantage. Their reliance on the wind for the distribution of their reproductive cells was always haphazard and expensive in biological terms. Spores do not require fertilisation and they will develop wherever they fall, provided the ground is sufficiently moist and fertile. Even so, the vast majority of them, from such a plant as a fern, fail to find the right conditions and die. The chances of survival for a wind-blown pollen grain are very much smaller still, for their requirements are even more precise and restricted. They can only develop and become effective if they happen to land on a female cone. So the pine tree has to produce pollen in gigantic quantities. A single small male cone produces several million grains, and if you tap one in spring, they fall out in such numbers that they create a golden cloud. A whole pine forest produces so much pollen that ponds become covered with curds of it – and all of it wasted.
Insects could provide a much more efficient transport system. If properly encouraged, they could carry the small amount of pollen necessary for fertilisation and place it on the exact spot in the female part of the plant where it was required. This courier service would be most economically operated if both pollen and egg were placed close together on the plant. The insects would then be able to make both deliveries and collections during the same call. And so developed the flower.
Some of the earliest and simplest of these marvellous devices so far identified are those produced by the magnolias. They appeared about a 100 million years ago. The eggs are clustered in the centre, each protected by a green coat with a receptive spike on the top called a stigma, on which the pollen must be placed if the eggs are to be fertilised. Grouped around the eggs are many stamens
