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