0:01:21 > 0:01:26Locusts. In the eyes of man, one of the greatest plagues on Earth.
0:01:26 > 0:01:28But from a less human point of view,
0:01:28 > 0:01:31they are dramatically successful members
0:01:31 > 0:01:37of a group that itself is the most numerous and varied kind of animal in the world.
0:01:37 > 0:01:39The insects.
0:01:39 > 0:01:43Like all insects, the locust's body is divided into three parts.
0:01:43 > 0:01:50A head, a middle section, and an abdomen that contains the digestive and reproductive organs.
0:01:52 > 0:01:56The middle section is full of muscle and carries six legs
0:01:56 > 0:01:59and usually a pair of wings.
0:02:01 > 0:02:04Its skeleton is external, like a shell,
0:02:04 > 0:02:08and it's made of chitin, a basically flexible material,
0:02:08 > 0:02:13but one which can be hardened to make mouth parts tough enough to cut through leaves,
0:02:13 > 0:02:16wood and even metal.
0:02:22 > 0:02:27There may be as many as a million million individual locusts
0:02:27 > 0:02:29in a single swarm like this.
0:02:29 > 0:02:31And these locusts are only one species.
0:02:31 > 0:02:34Science has so far described and labelled
0:02:34 > 0:02:37nearly a million species of insects,
0:02:37 > 0:02:42and there are probably two or three times as many still awaiting labels.
0:03:08 > 0:03:12The very first insects evolved some 300 million years ago.
0:03:12 > 0:03:16From the very beginning, many lived by eating plants,
0:03:16 > 0:03:20but in one way at least the plants benefited from their presence.
0:03:20 > 0:03:25They used them as messengers and recruited them with flowers.
0:03:27 > 0:03:32Magnolias have flowers very like the first flowers developed by any plants.
0:03:32 > 0:03:35They're relatively simple.
0:03:35 > 0:03:38They contain both male and female cells.
0:03:38 > 0:03:41The male cells come from these structures around here,
0:03:41 > 0:03:43in the pollen,
0:03:43 > 0:03:45and the female are buried
0:03:45 > 0:03:48at the base of this structure in the centre.
0:03:48 > 0:03:53Clearly, there's a strong chance this flower might fertilise itself,
0:03:53 > 0:03:58but there's a real advantage to be gained if the pollen can come to
0:03:58 > 0:04:00this female cell from another plant
0:04:00 > 0:04:05because that way, there's a greater chance of variation in the offspring.
0:04:05 > 0:04:09And variation is the raw material of evolution.
0:04:09 > 0:04:12And it's here that the insects help the plants.
0:04:12 > 0:04:18Beetles have probably fed on the spores of ferns and horsetails from early times.
0:04:18 > 0:04:23So there can have been little difficulty in attracting them to the pollen in the first flowers.
0:04:23 > 0:04:27Primitive moths also took to the habit very early.
0:04:27 > 0:04:32Of course, if the insects ate all the pollen, that wouldn't help the plant,
0:04:32 > 0:04:35but they're messy feeders, get grains all over them,
0:04:35 > 0:04:39and these brush off onto other flowers and fertilise them.
0:04:39 > 0:04:42So both plant and insect profit
0:04:42 > 0:04:45and the habit of pollen munching began to spread.
0:04:45 > 0:04:49The plants produced more pollen than they required for fertilisation,
0:04:49 > 0:04:54and all kinds of insects visited flowers to feast on it.
0:04:57 > 0:05:02The sexual reproduction of flowering plants ensures the variation in the offspring
0:05:02 > 0:05:05on which natural selection depends for evolution to take place.
0:05:05 > 0:05:10The greater the insect traffic from flower to flower and plant to plant,
0:05:10 > 0:05:13the greater the potential for variety and evolution.
0:05:17 > 0:05:22In time, the first flowers increased the prizes on offer.
0:05:22 > 0:05:24They produced sweet tasting nectar,
0:05:24 > 0:05:28and some insects turned their mouth parts into tubes
0:05:28 > 0:05:32so that they could probe deep into the flowers and sip it.
0:05:36 > 0:05:39But such delectable rewards had to be advertised.
0:05:39 > 0:05:45Some flowers became brilliantly coloured so that they were conspicuous even from a distance.
0:05:45 > 0:05:51Some also developed powerful perfumes to announce there was nectar on offer
0:05:51 > 0:05:53and pollen to be transported.
0:05:55 > 0:05:57The sheer beauty of flowers,
0:05:57 > 0:06:01their elegance of shape, the exquisite colours and patterns,
0:06:01 > 0:06:04are an endless source of delight to us.
0:06:04 > 0:06:07But flowers appeared on Earth millions of years before man,
0:06:07 > 0:06:10and they developed not to appeal to the human eye
0:06:10 > 0:06:13but to the eyes of insects.
0:06:13 > 0:06:16These designs are far from arbitrary.
0:06:16 > 0:06:21They are signals indicating where pollen and nectar can be found.
0:06:34 > 0:06:37These patterns of dots and lines
0:06:37 > 0:06:40are as precise as instructions on an airfield,
0:06:40 > 0:06:45showing the insect exactly where to land and which way to taxi.
0:06:45 > 0:06:50Many insects can see parts of the spectrum that are invisible to us, such as ultraviolet.
0:06:50 > 0:06:55So if we photograph a flower with film sensitive to ultraviolet light,
0:06:55 > 0:06:59we can get an insect-eye view of it, which is sometimes very different.
0:07:01 > 0:07:02This meadow cranesbill
0:07:02 > 0:07:05seems to have faint lines on its petals,
0:07:05 > 0:07:09but their ultraviolet markings are very distinct indeed.
0:07:13 > 0:07:16Other plants have adopted a different tactic.
0:07:16 > 0:07:19Instead of producing pollen in one place on a big flower,
0:07:19 > 0:07:24they produce many tiny flowers in a showy bunch,
0:07:24 > 0:07:28so that wherever visiting insects go, there is pollen and nectar to be gathered.
0:07:36 > 0:07:38Some have taken this design so far,
0:07:38 > 0:07:41that they have come to look like single flowers.
0:07:41 > 0:07:47The yellow mass in the centre of this daisy is made up of several hundred small flowers,
0:07:47 > 0:07:50each with its stamens and ovaries.
0:07:51 > 0:07:54So it is to insects and their sensitive eyes
0:07:54 > 0:07:56that we owe so much beauty.
0:07:56 > 0:08:01But there are many drab flowers - the hazel, for example.
0:08:01 > 0:08:06It's obvious these must rely on a quite different way of transporting pollen. The wind.
0:08:06 > 0:08:08The male flowers have to be large
0:08:08 > 0:08:13to produce the great quantities of pollen needed for such a haphazard method.
0:08:13 > 0:08:16But the female flower, with no need to advertise,
0:08:16 > 0:08:19is an inconspicuous little tuft.
0:08:21 > 0:08:25Oak trees use a similar system
0:08:25 > 0:08:28with separate male flowers that fill the atmosphere with pollen,
0:08:28 > 0:08:33only a tiny proportion of which rains down onto the place where it serves its most proper purpose -
0:08:33 > 0:08:35on the female flower.
0:08:37 > 0:08:42Some flowers use wind in a different way, to summon insects with perfume.
0:08:42 > 0:08:48The arum lily's intoxicating scent attracts them just as it pleases us.
0:08:48 > 0:08:51But some insects have different tastes from ours.
0:08:52 > 0:08:56The stapelia smells of rotting flesh,
0:08:56 > 0:09:01disgusting to us, but extremely attractive to flies that feed on carrion.
0:09:03 > 0:09:04And when they arrive,
0:09:04 > 0:09:06they find flowers that tempt them still further,
0:09:06 > 0:09:11for their petals actually resemble the wrinkled, decaying skin
0:09:11 > 0:09:12of a dead animal.
0:09:18 > 0:09:24The amorphophallus of the jungles of the Far East relies almost entirely on smell.
0:09:24 > 0:09:27The overpowering stench that comes from this huge bloom,
0:09:27 > 0:09:31as tall as a man, resembles that of rotting fish,
0:09:31 > 0:09:33mixed perhaps with a little burnt sugar.
0:09:33 > 0:09:38Its European relative, the modest wild arum or cuckoo pint of English hedgerows,
0:09:38 > 0:09:43also produces a faint, unpleasant smell as well as warmth.
0:09:43 > 0:09:47Having attracted numerous small flies, it then traps them.
0:09:47 > 0:09:52The lower part of the scent-producing rod secretes little drops of oil.
0:09:52 > 0:09:58Insect visitors lose their foothold and tumble past the slippery, downward-pointing hairs
0:09:58 > 0:10:01into the lower chamber, where the flowers are.
0:10:02 > 0:10:05The top ones are male, which are not yet mature.
0:10:05 > 0:10:07There's nothing here for the insects.
0:10:16 > 0:10:21Below the male flowers are the female flowers.
0:10:22 > 0:10:26The small flies, which may have visited other arums the previous day,
0:10:26 > 0:10:29now inadvertently spread pollen on them.
0:10:29 > 0:10:34But the insects can't escape. The oily hairs keep them imprisoned
0:10:34 > 0:10:37and they have to remain there all night.
0:10:40 > 0:10:45The next morning, the hairs, the bars of their prison, have shrivelled.
0:10:45 > 0:10:50The female flowers have closed their stigmas so they can no longer be fertilised,
0:10:50 > 0:10:53and secreted a tiny drop of honey as a reward.
0:10:53 > 0:10:57But the male flowers have opened and shed pollen over the flies,
0:10:57 > 0:11:02which are now free to look for another arum in which they may, inadvertently, spend the night.
0:11:05 > 0:11:11Pollen taken from one species of flower and deposited on a different species is wasted.
0:11:11 > 0:11:17So there's been a tendency in the insect-flower alliance for particular partnerships to develop
0:11:17 > 0:11:23and for one species of flower to become intimately involved with just one species of insect.
0:11:23 > 0:11:26The nectar of some flowers is hidden away and reserved
0:11:26 > 0:11:31for those insects with exactly the right mouth parts and feeding manners,
0:11:31 > 0:11:34and which will assiduously visit all the blooms of that species
0:11:34 > 0:11:37that they can manage during the flowering season.
0:11:38 > 0:11:45The salvia blossom only opens its doors when an insect of the particular weight and shape of a bee
0:11:45 > 0:11:51lands on its flight deck, triggering the stamens to stamp pollen on top of its abdomen.
0:12:02 > 0:12:09The flowers go on producing nectar, and a few days later their ovaries become mature.
0:12:11 > 0:12:16When a bee comes to visit them this time, it's the stigma projecting from the top of the ovary
0:12:16 > 0:12:20that jerks downwards and collects the pollen.
0:12:26 > 0:12:32This kind of relationship has led flowers away from the original circular designs like magnolias
0:12:32 > 0:12:36to develop complicated constructions of triggers and levers,
0:12:36 > 0:12:40delicately balanced platforms and slippery pits.
0:12:40 > 0:12:43The bloom has now become a kind of obstacle course,
0:12:43 > 0:12:46ensuring that the visitors are not able to collect their rewards
0:12:46 > 0:12:51without completing the essential service of transporting the pollen.
0:12:51 > 0:12:55The most complicated mechanisms of all are those produced by orchids.
0:12:55 > 0:12:59Even now, there are some we don't understand.
0:13:03 > 0:13:06This one, the flying duck orchid from Australia,
0:13:06 > 0:13:09has the most extraordinary action as it opens,
0:13:09 > 0:13:14but we don't know why it's shaped this way, why it moves like this
0:13:14 > 0:13:17or on what insect it relies to carry its pollen.
0:13:17 > 0:13:21This orchid attracts insects by sexual impersonation.
0:13:21 > 0:13:25It gives off a perfume like that of a female ichneumon wasp.
0:13:25 > 0:13:29When the male arrives, he finds something that not only smells like his female,
0:13:29 > 0:13:31but looks remarkably like her.
0:13:33 > 0:13:38At one end of the bloom, there's a mass of pollen stuck together into a horseshoe shape.
0:13:39 > 0:13:42The ichneumon male copulates with the flower.
0:13:49 > 0:13:55And the pollen mass is so placed that it fastens neatly onto his abdomen.
0:13:55 > 0:14:00In fact, this orchid is totally dependent on one species of ichneumon wasp for pollination
0:14:00 > 0:14:02and therefore reproduction.
0:14:02 > 0:14:07The orchid can only survive as long as the ichneumon wasps do.
0:14:21 > 0:14:24When the male insect copulates with the next flower,
0:14:24 > 0:14:27he delivers the pollen from the last.
0:14:39 > 0:14:41The yucca plant of Central America
0:14:41 > 0:14:45has a relationship with its insect partner that is so close
0:14:45 > 0:14:50that now both insect and plant are completely dependent on one another.
0:14:54 > 0:14:59The yucca's creamy blossoms are visited by tiny moths.
0:14:59 > 0:15:05During the day, the moths spend a lot of time moving from flower to flower and inspecting them.
0:15:05 > 0:15:07All are not at the same stage of development.
0:15:07 > 0:15:13The stamens become mature first and split open, and it's these that the moth is looking for.
0:15:15 > 0:15:19In the late afternoon, the female moth, having already mated,
0:15:19 > 0:15:22is collecting pollen from suitable flowers.
0:15:36 > 0:15:39She's now gathered the pollen into a tight ball
0:15:39 > 0:15:41which she holds under her head as she searches
0:15:41 > 0:15:46for other flowers which are in a different state of development.
0:15:51 > 0:15:55This time, she's more interested in the central part of the flower,
0:15:55 > 0:16:00and takes up a position alongside one of the ovaries, which have a green-tipped stigma.
0:16:00 > 0:16:04Here she will stay for about 20 minutes.
0:16:04 > 0:16:08Her egg-laying tube is deep at the bottom of the flower's ovary,
0:16:08 > 0:16:11and she's laying her own eggs there.
0:16:15 > 0:16:16Having finished laying,
0:16:16 > 0:16:20she separates some pollen grains from the ball she's collected
0:16:20 > 0:16:25and smears them into the stigma with mouth parts specially developed for the purpose.
0:16:44 > 0:16:47Now she will repeat the entire procedure
0:16:47 > 0:16:49in other ovaries of the flower.
0:16:59 > 0:17:01The egg-laying position again.
0:17:11 > 0:17:14Again she will pollinate the flower.
0:17:16 > 0:17:20First she removes a small amount of pollen from the ball she's holding.
0:17:24 > 0:17:26By pollinating the flower,
0:17:26 > 0:17:29she serves not only the yucca but her own offspring,
0:17:29 > 0:17:33for she ensures the eggs in the ovary below will develop
0:17:33 > 0:17:39so that her caterpillars when they hatch will have a rich source of food immediately to hand.
0:17:40 > 0:17:43But the caterpillars won't eat all the seeds.
0:17:43 > 0:17:47The moths don't lay as many eggs as that. So when the yucca comes into fruit,
0:17:47 > 0:17:53there are plenty of undamaged seeds to ensure that new plants will appear.
0:17:53 > 0:17:55But the balance is a very delicate one.
0:17:55 > 0:18:00If it went wrong, it could be disastrous for both plants and insect.
0:18:00 > 0:18:03Without the moth, the yucca would not be pollinated.
0:18:03 > 0:18:08Nothing else has those specially modified mouth parts for pressing the pollen into the style.
0:18:08 > 0:18:12And without the yucca, the moth's caterpillars would starve.
0:18:14 > 0:18:17The seductive odours and beguiling shapes of flowers
0:18:17 > 0:18:20are so attractive to the insects for whom they're designed
0:18:20 > 0:18:23that they find them virtually irresistible.
0:18:23 > 0:18:27Other insects turn that to their advantage in a different way.
0:18:32 > 0:18:36This ginger flower has petals that move.
0:18:37 > 0:18:40It's one of the most extravagant designs of any insect.
0:18:40 > 0:18:47For this, with flaps on its legs that match the petals of the flower, is a mantis.
0:19:15 > 0:19:18The butterfly comes to sip nectar.
0:19:41 > 0:19:47There are many different kinds of mantis, all marvellously camouflaged,
0:19:47 > 0:19:50all voracious hunters.
0:19:50 > 0:19:52The flesh of an insect is succulent,
0:19:52 > 0:19:56but to get at it the mantis has to deal with the external skeleton,
0:19:56 > 0:19:58the shell of chitin.
0:19:58 > 0:20:01Chitin is dead material. It won't expand.
0:20:01 > 0:20:07It's one of the few limitations to the insect body that is otherwise so versatile.
0:20:07 > 0:20:11In order to grow, all insects have to shed their skin at regular intervals,
0:20:11 > 0:20:14and this bug is just about to do so.
0:20:14 > 0:20:20A new, soft skin has formed underneath, and by sucking in air and inflating itself,
0:20:20 > 0:20:24the bug is cracking its old skin.
0:20:55 > 0:20:59Once free, the bug inflates itself still further,
0:20:59 > 0:21:04stretching out the crinkles in its soft skin and expanding.
0:21:04 > 0:21:07After an hour or so, its new skeleton has hardened.
0:21:13 > 0:21:17A spiny leaf insect is just about to do the same trick.
0:21:56 > 0:21:59Its old shell hangs from the branch above it
0:21:59 > 0:22:01like the ghost of its former self.
0:22:06 > 0:22:08But the more complicated an insect's body,
0:22:08 > 0:22:13the more laborious and difficult this process of skin shedding becomes.
0:22:13 > 0:22:18And some insects not only simplify it but exploit different food sources
0:22:18 > 0:22:20by leading split lives.
0:22:20 > 0:22:25This creature emerging from the egg will eventually become a butterfly.
0:22:25 > 0:22:29But for the first part of its life, it will keep its body simple.
0:22:29 > 0:22:31A caterpillar.
0:22:31 > 0:22:35A caterpillar is little more than an eating machine.
0:22:35 > 0:22:39This one starts its life as it means to go on by eating its own eggshell.
0:22:45 > 0:22:49The caterpillar's existence is totally dedicated to food.
0:22:49 > 0:22:53It won't breed, so it doesn't need sexual organs.
0:22:53 > 0:22:55It has no cause to attract a mate,
0:22:55 > 0:22:58so it need not send out any signals to one
0:22:58 > 0:23:01or develop wings so it can fly off and look for one.
0:23:01 > 0:23:04Its parents have gone to a great deal of trouble
0:23:04 > 0:23:07to ensure it finds ample food immediately to hand,
0:23:07 > 0:23:11so all it really needs is an efficient pair of jaws
0:23:11 > 0:23:14and, behind them, a bag-like expandable body.
0:23:18 > 0:23:22But if a caterpillar's body is to expand,
0:23:22 > 0:23:25it can't have a hard, rigid external skeleton.
0:23:25 > 0:23:29Just a thin, flexible skin that is easily shed and replaced.
0:23:29 > 0:23:31And that could leave it vulnerable.
0:23:31 > 0:23:35So caterpillars have to have other ways of protecting themselves.
0:23:35 > 0:23:37Some do it by bluff,
0:23:37 > 0:23:40developing markings that look like fearsome eyes.
0:23:47 > 0:23:51Some rely on camouflage initially, and if that doesn't work,
0:23:51 > 0:23:54they too try to startle.
0:24:01 > 0:24:03The caterpillar of an Australian swallowtail
0:24:03 > 0:24:07looks convincingly like a glistening bird dropping,
0:24:07 > 0:24:10and if any predator thinks that's worth investigating,
0:24:10 > 0:24:14then it suddenly, and unexpectedly, produces strange antennae.
0:24:23 > 0:24:26Many caterpillars sprout long hairs tipped with poison
0:24:26 > 0:24:32that can cause quite a rash on a human skin and certainly put off a lot of birds.
0:24:32 > 0:24:36To make sure that would-be predators are in no doubt they're unpalatable,
0:24:36 > 0:24:40the caterpillars advertise themselves with bright warning colours.
0:24:45 > 0:24:48So, with the best protection they can muster,
0:24:48 > 0:24:51the caterpillars industriously pack away their food,
0:24:51 > 0:24:56slipping off their thin but often flamboyant skins when a bigger one is required
0:24:56 > 0:24:59until they have grown as much as they need.
0:24:59 > 0:25:04And then they prepare for the first of two highly dramatic transformations.
0:25:14 > 0:25:19Many moths make the change in private behind a silken shroud.
0:25:19 > 0:25:22Industriously, they spin and weave.
0:25:42 > 0:25:47This one adds tiny pieces of bark to camouflage the cocoon.
0:25:51 > 0:25:57Some of those that had poisonous bristles shed them in their final moult within their cocoons
0:25:57 > 0:26:00and weave them into their wrappings
0:26:00 > 0:26:02so that they will continue to protect them.
0:26:35 > 0:26:37And now, all seems still.
0:26:37 > 0:26:40Life, apparently, is suspended.
0:26:40 > 0:26:44But inside, a profound revolution is taking place.
0:26:44 > 0:26:48The caterpillar's body is breaking down into a kind of soup.
0:26:48 > 0:26:52Clusters of cells that have remained dormant since the creature emerged from the egg
0:26:52 > 0:26:59now become active, absorbing the soup, multiplying and reassembling a new body
0:26:59 > 0:27:03from all the material that the caterpillar so industriously gathered.
0:27:03 > 0:27:08Most butterfly caterpillars embark on this change unscreened by a cocoon.
0:27:08 > 0:27:13Though usually inconspicuously close to a stem or under a leaf.
0:27:13 > 0:27:19The Australian common crow caterpillar first spins a silk thread, from which it hangs.
0:27:23 > 0:27:27Beneath its skin it has secreted a new and different one.
0:27:27 > 0:27:33The old skin splits and rolls off, taking with it the hard parts for which there's no more use,
0:27:33 > 0:27:38the tiny claws from the legs and those hard-worked jaws.
0:27:47 > 0:27:51The new skin hardens and in a few hours becomes mirror-like,
0:27:51 > 0:27:55reflecting the foliage around it for better camouflage.
0:27:59 > 0:28:02The body of a butterfly may take months to rebuild,
0:28:02 > 0:28:04or as little as a week.
0:28:22 > 0:28:27The wings are crumpled bags, but the insect pumps blood into them
0:28:27 > 0:28:30and slowly they expand.
0:28:38 > 0:28:44The wings dry and harden, and the Australian orchard butterfly is ready for flight.
0:28:47 > 0:28:52The primary task now of all these butterflies is to find a mate.
0:28:53 > 0:28:57Scent is used to locate their mates over long distances,
0:28:57 > 0:29:00and now their gorgeous wings carry them on the search,
0:29:00 > 0:29:04proclaiming with their colours and patterns their identities
0:29:04 > 0:29:08and so attracting mates of the same species at close range.
0:29:08 > 0:29:11They still feed on nectar to provide them with the energy to fly,
0:29:11 > 0:29:15but they don't need any food to build or renew their tissues.
0:29:15 > 0:29:18The time for growth is over.
0:29:37 > 0:29:43The birdwing butterflies of the Far East are among the largest and most graceful.
0:30:17 > 0:30:21Male and female butterflies meet and courtship begins.
0:30:36 > 0:30:40Successful males couple with females by joining abdomens.
0:30:59 > 0:31:02These marvellous, elaborate structures, the wings,
0:31:02 > 0:31:09each clothed by thousands of microscopic scales arranged in intricate patterns,
0:31:09 > 0:31:13have, within a few days, in some species within a few hours,
0:31:13 > 0:31:15completed their purpose.
0:31:15 > 0:31:18Male and female have found one another
0:31:18 > 0:31:20and the cycle will begin again.
0:31:22 > 0:31:29The atlas moth is one of the biggest of all butterflies and moths.
0:31:30 > 0:31:34But its body, of course, is small compared with that of a bird.
0:31:34 > 0:31:40The reason is because of another limitation to the basic insect body design.
0:31:40 > 0:31:47This moth, like all insects, breathes through a series of holes along its flank.
0:31:47 > 0:31:50They're the openings of tubes, with many branches,
0:31:50 > 0:31:52that extend throughout the body
0:31:52 > 0:31:55and carry oxygen to every individual organ.
0:31:55 > 0:31:58It's a system that works by diffusion.
0:31:58 > 0:32:01It works very well over short distances.
0:32:01 > 0:32:06But as the length of the tube increases, it becomes less efficient,
0:32:06 > 0:32:09and eventually it becomes impossible.
0:32:09 > 0:32:14That's why there are no moths or butterflies the size of eagles.
0:32:26 > 0:32:30The insects have, however, found one way of transcending
0:32:30 > 0:32:32this problem of the limitation of size.
0:32:32 > 0:32:37Numbers. In this one single termite hill,
0:32:37 > 0:32:41there must live two or three million insects.
0:32:41 > 0:32:45But there are good reasons for considering them not as individuals
0:32:45 > 0:32:50but as together constituting one single great super-organism.
0:32:50 > 0:32:54A super-organism that simply in terms of animal tissue alone
0:32:54 > 0:32:56must weigh as much as an antelope
0:32:56 > 0:33:01and which certainly crops the surrounding vegetation as heavily as an antelope.
0:33:01 > 0:33:04And when you look at these super-organisms
0:33:04 > 0:33:06out here in Western Australia,
0:33:06 > 0:33:10they seem to dominate the landscape just as powerfully
0:33:10 > 0:33:14as antelope dominate the plains of East Africa.
0:33:20 > 0:33:24This type of colony is not just a haphazard collection of individuals
0:33:24 > 0:33:27who've decided to share the same dwelling,
0:33:27 > 0:33:29like human beings in a tower block.
0:33:29 > 0:33:34For one thing, they're all one family. All the children of a single, gigantic female.
0:33:34 > 0:33:37For another, they're all incomplete creatures.
0:33:37 > 0:33:40Not one of them could survive by itself for long.
0:33:40 > 0:33:43These workers are all sterile.
0:33:55 > 0:34:00The soldiers, which defend the community, have such huge jaws
0:34:00 > 0:34:03that they can't feed themselves.
0:34:03 > 0:34:06And the queen, in the middle of the colony, is so huge
0:34:06 > 0:34:10that she can't move and has to have food brought to her.
0:34:10 > 0:34:13She's a gigantic egg machine.
0:34:13 > 0:34:17The workers bring food to one end and collect eggs from the other
0:34:17 > 0:34:22which she produces at the almost unbelievable rate of 30,000 a day.
0:34:22 > 0:34:26The male, the size of a wasp, lies alongside her.
0:34:26 > 0:34:29She has a controlling effect on the activity of the colony.
0:34:29 > 0:34:34She sweats a chemical substance which the workers obtain by licking her body,
0:34:34 > 0:34:38and this in effect gives them their instructions.
0:34:38 > 0:34:40It stimulates them to do certain things.
0:34:40 > 0:34:43To feed the young grubs on a particular diet,
0:34:43 > 0:34:46to move the eggs into special places.
0:34:48 > 0:34:52At one moment, either because of a change in the queen's instructions
0:34:52 > 0:34:55or because the eggs she lays are slightly different,
0:34:55 > 0:35:00they hatch not into sterile workers but into sexually mature adults,
0:35:00 > 0:35:02both male and female.
0:35:04 > 0:35:08And then, suddenly, the colony seems to smoke
0:35:08 > 0:35:15as thousands upon thousands of individuals emerge to fly off and colonise the surrounding country.
0:35:37 > 0:35:41When they land, their wings break off. They won't be needed again.
0:35:41 > 0:35:46Now the male and female begin their courtship dances.
0:35:58 > 0:35:59Once they've paired,
0:35:59 > 0:36:03they find a crevice and start to build themselves a nest.
0:36:03 > 0:36:06He fertilises her, she will lay eggs,
0:36:06 > 0:36:10and so together they will found a new colony.
0:36:10 > 0:36:15A new royal egg machine will go into full production and the various castes of individuals
0:36:15 > 0:36:18will hatch and grow.
0:36:23 > 0:36:29Highly organised social behaviour like this seems to have evolved several times among insects.
0:36:29 > 0:36:32Once among termites, related to cockroaches,
0:36:32 > 0:36:36and several times among the ants, bees and wasps.
0:36:36 > 0:36:38All three groups have mouth parts
0:36:38 > 0:36:41adapted for chewing so they can easily build nests.
0:36:46 > 0:36:50The wasps also use theirs for manipulating prey.
0:36:55 > 0:36:58Having paralysed their prey with a sting,
0:36:58 > 0:37:01some wasps pack them into their cells with the eggs
0:37:01 > 0:37:03so their young will have fresh meat when they hatch.
0:37:05 > 0:37:07Not all wasps and bees are social.
0:37:07 > 0:37:09Many of them are solitary,
0:37:09 > 0:37:12digging and stocking only their own cells.
0:37:14 > 0:37:17Sometimes, however, the scarcity of suitable nesting places
0:37:17 > 0:37:22causes otherwise solitary bees to breed close to one another.
0:37:25 > 0:37:28When these adult bees of this species emerge from their pupae,
0:37:28 > 0:37:32the males fight one another in order to mate with the females.
0:37:41 > 0:37:44Other species of bee that nest in similar sites
0:37:44 > 0:37:47are little more socially inclined.
0:37:47 > 0:37:53By this Kansas river, a group of little sweat bees are nesting in a burrow with one entrance hole.
0:37:54 > 0:38:00A guard bee stands like a sentry at the entrance and allows only its own species to enter.
0:38:01 > 0:38:04New arrivals appear to be instructed what to do
0:38:04 > 0:38:06by the bee that is moving backwards.
0:38:06 > 0:38:11She appears to be the dominant bee in the small colony.
0:38:11 > 0:38:14Other bees that seem to be identical in form
0:38:14 > 0:38:16apparently accept subordinate roles,
0:38:16 > 0:38:20taking on such jobs as building new chambers.
0:38:20 > 0:38:22Other chambers are complete.
0:38:22 > 0:38:26They already contain eggs or larvae at various stages of development,
0:38:26 > 0:38:29together with a ball of pollen for food.
0:38:35 > 0:38:37While all the work goes on,
0:38:37 > 0:38:40one dominant bee appears to control the group's activities.
0:38:40 > 0:38:44This bee can probably recognise others by their smell.
0:38:44 > 0:38:48Certainly, taste and smell play a vital part in the coordination
0:38:48 > 0:38:50of really big and complex insect colonies
0:38:50 > 0:38:53like those of the honey bee.
0:38:57 > 0:39:02Workers here are continually collecting chemical substances from the queen.
0:39:02 > 0:39:08She is the particularly large insect here inspecting new cells before depositing eggs in them.
0:39:14 > 0:39:19The chemical messages she produces circulate throughout the colony
0:39:19 > 0:39:23because of the workers' habit of exchanging spittle.
0:39:24 > 0:39:29Unlike termites, who travel over land to find food, bees fly.
0:39:29 > 0:39:32So they're unable to lay a scent trail on the ground.
0:39:32 > 0:39:37Bees have had to evolve a different method of telling co-workers where the food is.
0:39:39 > 0:39:43When a worker returns from a new, rich source of food,
0:39:43 > 0:39:45it goes onto the vertical cones,
0:39:45 > 0:39:48its satchels on its legs packed with yellow pollen.
0:39:51 > 0:39:54After exchanging spittle, it dances.
0:39:54 > 0:39:59That waggling dance is about 20 degrees to the left of vertical,
0:39:59 > 0:40:03and that means that the flower she's discovered can be found by flying
0:40:03 > 0:40:05about 20 degrees to the left of the sun.
0:40:12 > 0:40:14The other workers "read" the dance,
0:40:14 > 0:40:18which is accompanied by noises which some people believe also carry information.
0:40:22 > 0:40:27On leaving the hive, the workers remember the angle of the dance
0:40:27 > 0:40:30and set off at the same angle to the left of the sun.
0:40:30 > 0:40:33Because they can see polarised light,
0:40:33 > 0:40:36the bees don't even have to wait for a cloudless day.
0:40:39 > 0:40:44The origin of these colonies of insects presents quite a puzzle.
0:40:44 > 0:40:47It's a basic principle of evolution by natural selection
0:40:47 > 0:40:51that individual animals are engaged in a struggle
0:40:51 > 0:40:56to survive, to breed and pass on their genes to the next generation.
0:40:56 > 0:41:00How could it have been, then, that in the past there was some insect
0:41:00 > 0:41:06that actually gave up that right and laboured to help another insect
0:41:06 > 0:41:10pass on her genes to the next generation?
0:41:10 > 0:41:15The answer seems to lie in the particular way that these insects reproduce.
0:41:16 > 0:41:21Before the queen began laying, she was fertilised by several males called drones.
0:41:21 > 0:41:26She stored their sperm in her body, but withheld it when laying to produce males
0:41:26 > 0:41:30so they would carry only her genes.
0:41:32 > 0:41:39When she lays in cells to produce female workers, she fertilises the eggs by releasing some sperm.
0:41:39 > 0:41:43Occasionally, one of these females is allowed to develop into a new queen,
0:41:43 > 0:41:50and eventually the old queen will leave in a swarm with her sister workers to start a new colony.
0:41:50 > 0:41:52The net result of this complicated system
0:41:52 > 0:41:56is that the female workers and their nieces by their new sister queen
0:41:56 > 0:41:58are unusually closely related.
0:41:58 > 0:42:02In other words, they share a high proportion of common genes.
0:42:05 > 0:42:10And so, when these sterile workers labour away for the benefit of a colony,
0:42:10 > 0:42:14in order to help the queen pass on her genes to the next generation,
0:42:14 > 0:42:18they are in fact labouring on behalf of their own genes.
0:42:18 > 0:42:23The insects that have brought this to a particularly high level
0:42:23 > 0:42:26are the ants.
0:42:26 > 0:42:30Their similar methods of reproduction and skill at manipulation
0:42:30 > 0:42:36seems to be the reason why they too have evolved amazing social systems.
0:42:36 > 0:42:38The green tree ants of Southeast Asia
0:42:38 > 0:42:40cooperate in a most complex way to build their nests.
0:42:40 > 0:42:46Groups of workers hold two leaves together, gripping them with their legs and jaws
0:42:46 > 0:42:48to form a living bond.
0:42:50 > 0:42:54Other workers bring the young grubs from the centre of the nest,
0:42:54 > 0:42:59and by giving them little squeezes, stimulate them to produce silk.
0:42:59 > 0:43:01Then, using them like tubes of glue,
0:43:01 > 0:43:04they move them back and forth between the two leaves
0:43:04 > 0:43:07until they fasten them together with a sheet of silk.
0:43:18 > 0:43:22The cooperative behaviour of the ants holding the leaf
0:43:22 > 0:43:27starts usually with one isolate individual who succeeds in bending over part of the leaf,
0:43:27 > 0:43:30usually near the tip, where it's easy.
0:43:30 > 0:43:33This seems to act as a signal for other ants to join in,
0:43:33 > 0:43:36leaving whatever other tasks they're engaged in.
0:43:50 > 0:43:55In these ants, the workers are divided into a major and a minor caste.
0:43:55 > 0:43:58The major castes consists of workers who go out and do the foraging
0:43:58 > 0:44:02and the minor castes are employed as nurses, looking after the larvae.
0:44:08 > 0:44:13In South America, the parasol ants strip trees of their leaves,
0:44:13 > 0:44:17cutting them up into pieces and carrying them one by one
0:44:17 > 0:44:20into their vast underground nests.
0:44:20 > 0:44:22The work goes on night and day,
0:44:22 > 0:44:25hundreds of thousands of ants swarming all over the trees.
0:44:48 > 0:44:52The technique of carrying a leaf many times bigger than the ant
0:44:52 > 0:44:58depends on the worker tucking its head down onto its thorax before taking a grip.
0:45:21 > 0:45:25Sometimes they carry these segments for 100 yards,
0:45:25 > 0:45:33along trails that have been worn smooth by millions of tiny footsteps, day after day.
0:45:36 > 0:45:39The ants will not eat these leaves. They can't.
0:45:39 > 0:45:46Unlike termites, which have single-celled organisms in their guts to enable them to digest cellulose.
0:45:46 > 0:45:50The ants are collecting leaves in order to chew them up and make a kind of compost.
0:45:50 > 0:45:54On that, they cultivate a fungus in their underground galleries.
0:45:56 > 0:46:00The fungus supplies the ants with special juicy branches for their food,
0:46:00 > 0:46:06and the ants garden it with their own faeces and a special antibiotic dressing for a good yield.
0:46:09 > 0:46:14The ants have regular refuse tips on the surface, not far from the nest.
0:46:20 > 0:46:24Every now and then, the workers will suddenly stop dismantling trees
0:46:24 > 0:46:28and turn their attention to cleaning out the nest.
0:46:59 > 0:47:03The fungus which the parasol ants grow can survive nowhere else.
0:47:03 > 0:47:07They are utterly dependent on one another.
0:47:08 > 0:47:11Other ants have similar relationships with trees,
0:47:11 > 0:47:15with the trees actually encouraging the ants to take up residence.
0:47:15 > 0:47:20Some acacia trees in Central America have thorns for defence.
0:47:20 > 0:47:24But these needle-sharp thorns are doubly dangerous
0:47:24 > 0:47:29because inside them live colonies of aggressive stinging ants.
0:47:33 > 0:47:37Each pair of thorns has an entrance hole near the tip of one of them.
0:47:37 > 0:47:40The spongy cells that once filled the thorns
0:47:40 > 0:47:44have been chewed away to make a strong and safe brood chamber
0:47:44 > 0:47:47that becomes crammed with eggs and developing larvae.
0:47:57 > 0:48:00The ants never have to leave the tree to feed,
0:48:00 > 0:48:05for the acacia provides the colony with a beautifully balanced diet.
0:48:05 > 0:48:11The tiny reddish-brown beads on the leaflet tips are rich in fats, proteins and vitamins.
0:48:11 > 0:48:13Ideal food for developing insects,
0:48:13 > 0:48:16although they have no real function for the tree.
0:48:16 > 0:48:21The beads develop on the new leaves and at the tips of the shoots,
0:48:21 > 0:48:26so the attendant ants are in a perfect position to protect the most vulnerable part of the plant.
0:48:41 > 0:48:43The acacia also has nectaries,
0:48:43 > 0:48:46but these are not part of its flowers.
0:48:46 > 0:48:49The nectaries are situated at the base of the leaves,
0:48:49 > 0:48:55and the sole function is to provide the ants with the sugary liquid of which they're extremely fond.
0:48:59 > 0:49:03What, then, does the acacia get in return for these services?
0:49:03 > 0:49:08The answer is defence. The ants are particularly ferocious
0:49:08 > 0:49:11and defend the tree against any other insects that come to feed on it.
0:49:11 > 0:49:17What's more, they also drive off any grazing animal that tries to eat the foliage.
0:49:17 > 0:49:22And even mutilate and kill climbing vines that try to cover the host tree.
0:49:22 > 0:49:26As a result, in tropical areas where competition is intense,
0:49:26 > 0:49:31the acacia trees and their ants are a particularly successful team.
0:49:36 > 0:49:40The most aggressive ants of all are the army ants
0:49:40 > 0:49:43that build no permanent nest at all.
0:49:43 > 0:49:47They also have one of the most advanced societies of all insects.
0:49:52 > 0:49:56This colony has been temporarily camped overnight.
0:49:56 > 0:49:58Somewhere in the middle of this living ball
0:49:58 > 0:50:04is the queen and immature ants protected by the bodies of the workers.
0:50:04 > 0:50:08They make their own bivouac by linking their legs and bodies together
0:50:08 > 0:50:10with strong tiny claws.
0:50:19 > 0:50:23At first light, in the morning, the colony will begin to disperse.
0:50:23 > 0:50:27Between 150 and 170,000 workers may be present,
0:50:27 > 0:50:32and some of them must carry the queen and larvae as the column moves off on a foray
0:50:32 > 0:50:37guarded by the huge soldiers, whose only job is defence.
0:50:38 > 0:50:43For two or three weeks, the army ants make a new bivouac each night.
0:50:43 > 0:50:45Then their behaviour will change
0:50:45 > 0:50:47and they will make a semi-permanent home,
0:50:47 > 0:50:50often in a hollow tree.
0:50:53 > 0:50:55The queen is now ready to lay eggs.
0:50:55 > 0:50:59Over a few days, protected by her living shelter of workers,
0:50:59 > 0:51:03she will lay between 100,000 and 300,000 eggs.
0:51:03 > 0:51:06After three weeks, the larvae hatch.
0:51:06 > 0:51:10And because of chemical secretions produced by these new recruits,
0:51:10 > 0:51:14the colony is once more galvanised into great activity.
0:51:18 > 0:51:23Now the nomadic phase begins again and the army goes to war.
0:51:23 > 0:51:28They will kill every living creature in their path that can't run from them.
0:51:41 > 0:51:45Normally they hunt other insects, but they will take small reptiles
0:51:45 > 0:51:50and even kill dogs and cows if they're tethered and can't escape.
0:51:50 > 0:51:53If the termite colony could be compared to an antelope,
0:51:53 > 0:51:59then this formidable super-organism must be the insect equivalent of a beast of prey.
0:51:59 > 0:52:05As powerful, ferocious and long-lived as many hunters of the jungle.
0:52:07 > 0:52:11Whatever limitations there may be in being small,
0:52:11 > 0:52:13these army ants and other social insects
0:52:13 > 0:52:15seem to have overcome them.
0:52:15 > 0:52:22Indeed, the more closely one watches insects, the more deeply impressed one is by their efficiency.
0:52:22 > 0:52:28No matter what man may wish to believe, insects are still masters of great parts of the world.
0:52:28 > 0:52:32They were, after all, the first animals to emerge onto dry land.
0:52:32 > 0:52:35Then they lived by exploiting plants.
0:52:35 > 0:52:39Hundreds of thousands of species of them still do so today,
0:52:39 > 0:52:43chewing the leaves, gnawing the seeds and drinking the sap.
0:52:43 > 0:52:47And when other animals joined the insects on dry land,
0:52:47 > 0:52:49the insects exploited them too.
0:52:49 > 0:52:52They drank their blood, burrowed into their skins,
0:52:52 > 0:52:56they actually found a home within the tissues of living animals.
0:52:56 > 0:52:59Man has been doing battle with the insects
0:52:59 > 0:53:04ever since he first picked off the first flea and, I dare say, long before.
0:53:04 > 0:53:09Today we continue the fight, with fire, with radioactivity,
0:53:09 > 0:53:14with the most lethal poisons our chemists have been able to devise.
0:53:14 > 0:53:19And yet, so far, we have not managed to exterminate a single species.