1 00:01:21,400 --> 00:01:22,680 Locusts. 2 00:01:22,680 --> 00:01:26,720 In the eyes of man, one of the greatest plagues on Earth. 3 00:01:26,720 --> 00:01:28,760 But from a less human point of view, 4 00:01:28,760 --> 00:01:33,400 they are dramatically successful members of a group that itself 5 00:01:33,400 --> 00:01:37,680 is the most numerous and varied kind of animal in the world. 6 00:01:37,680 --> 00:01:39,120 The insects. 7 00:01:39,120 --> 00:01:43,920 Like all insects, the locust's body is divided into three parts. 8 00:01:43,920 --> 00:01:48,920 A head, a middle section, and an abdomen that contains the digestive 9 00:01:48,920 --> 00:01:50,880 and reproductive organs. 10 00:01:52,120 --> 00:01:56,440 The middle section is full of muscle and carries six legs 11 00:01:56,440 --> 00:01:59,080 and usually a pair of wings. 12 00:02:01,200 --> 00:02:04,640 Its skeleton is external, like a shell, 13 00:02:04,640 --> 00:02:08,960 and it's made of chitin, a basically flexible material, 14 00:02:08,960 --> 00:02:12,320 but one which can be hardened to make mouth parts tough enough 15 00:02:12,320 --> 00:02:15,680 to cut through leaves, wood and even metal. 16 00:02:22,760 --> 00:02:27,040 There may be as many as a million million individual locusts 17 00:02:27,040 --> 00:02:29,040 in a single swarm like this. 18 00:02:29,040 --> 00:02:31,800 And these locusts are only one species. 19 00:02:31,800 --> 00:02:34,920 Science has so far described and labelled 20 00:02:34,920 --> 00:02:37,720 nearly a million species of insects, 21 00:02:37,720 --> 00:02:42,400 and there are probably two or three times as many still awaiting labels. 22 00:03:08,120 --> 00:03:12,920 The very first insects evolved some 300 million years ago. 23 00:03:12,920 --> 00:03:16,280 From the very beginning, many lived by eating plants, 24 00:03:16,280 --> 00:03:20,600 but in one way at least the plants benefited from their presence. 25 00:03:20,600 --> 00:03:25,520 They used them as messengers and recruited them with flowers. 26 00:03:27,200 --> 00:03:31,040 Magnolias have flowers very like the first flowers 27 00:03:31,040 --> 00:03:32,960 developed by any plants. 28 00:03:32,960 --> 00:03:35,360 They're relatively simple. 29 00:03:35,360 --> 00:03:38,760 They contain both male and female cells. 30 00:03:38,760 --> 00:03:41,280 The male cells come from these structures around here, 31 00:03:41,280 --> 00:03:43,040 in the pollen, 32 00:03:43,040 --> 00:03:45,000 and the female are buried 33 00:03:45,000 --> 00:03:48,360 at the base of this structure in the centre. 34 00:03:48,360 --> 00:03:53,160 Clearly, there's a strong chance this flower might fertilise itself, 35 00:03:53,160 --> 00:03:58,080 but there's a real advantage to be gained if the pollen can come to 36 00:03:58,080 --> 00:04:00,840 this female cell from another plant 37 00:04:00,840 --> 00:04:05,160 because that way, there's a greater chance of variation in the offspring. 38 00:04:05,160 --> 00:04:09,000 And variation is the raw material of evolution. 39 00:04:09,000 --> 00:04:12,440 And it's here that the insects help the plants. 40 00:04:12,440 --> 00:04:16,920 Beetles have probably fed on the spores of ferns and horsetails 41 00:04:16,920 --> 00:04:18,240 from early times. 42 00:04:18,240 --> 00:04:21,520 So there can have been little difficulty in attracting them 43 00:04:21,520 --> 00:04:23,720 to the pollen in the first flowers. 44 00:04:23,720 --> 00:04:27,800 Primitive moths also took to the habit very early. 45 00:04:27,800 --> 00:04:32,400 Of course, if the insects ate all the pollen, that wouldn't help the plant, 46 00:04:32,400 --> 00:04:35,280 but they're messy feeders, get grains all over them, 47 00:04:35,280 --> 00:04:39,640 and these brush off onto other flowers and fertilise them. 48 00:04:39,640 --> 00:04:42,000 So both plant and insect profit 49 00:04:42,000 --> 00:04:45,840 and the habit of pollen munching began to spread. 50 00:04:45,840 --> 00:04:49,520 The plants produced more pollen than they required for fertilisation, 51 00:04:49,520 --> 00:04:54,200 and all kinds of insects visited flowers to feast on it. 52 00:04:57,200 --> 00:05:01,520 The sexual reproduction of flowering plants ensures the variation in the 53 00:05:01,520 --> 00:05:05,920 offspring on which natural selection depends for evolution to take place. 54 00:05:05,920 --> 00:05:10,240 The greater the insect traffic from flower to flower and plant to plant, 55 00:05:10,240 --> 00:05:13,640 the greater the potential for variety and evolution. 56 00:05:17,600 --> 00:05:22,160 In time, the first flowers increased the prizes on offer. 57 00:05:22,160 --> 00:05:24,560 They produced sweet-tasting nectar, 58 00:05:24,560 --> 00:05:28,400 and some insects turned their mouth parts into tubes 59 00:05:28,400 --> 00:05:32,000 so that they could probe deep into the flowers and sip it. 60 00:05:36,680 --> 00:05:39,520 But such delectable rewards had to be advertised. 61 00:05:39,520 --> 00:05:43,320 Some flowers became brilliantly coloured so that they were 62 00:05:43,320 --> 00:05:45,560 conspicuous even from a distance. 63 00:05:45,560 --> 00:05:51,080 Some also developed powerful perfumes to announce there was nectar on offer 64 00:05:51,080 --> 00:05:53,920 and pollen to be transported. 65 00:05:55,400 --> 00:05:57,240 The sheer beauty of flowers, 66 00:05:57,240 --> 00:06:01,440 their elegance of shape, the exquisite colours and patterns, 67 00:06:01,440 --> 00:06:04,240 are an endless source of delight to us. 68 00:06:04,240 --> 00:06:07,600 But flowers appeared on Earth millions of years before man, 69 00:06:07,600 --> 00:06:10,960 and they developed not to appeal to the human eye 70 00:06:10,960 --> 00:06:13,040 but to the eyes of insects. 71 00:06:13,040 --> 00:06:16,240 These designs are far from arbitrary. 72 00:06:16,240 --> 00:06:21,320 They are signals indicating where pollen and nectar can be found. 73 00:06:34,720 --> 00:06:37,080 These patterns of dots and lines 74 00:06:37,080 --> 00:06:40,520 are as precise as instructions on an airfield, 75 00:06:40,520 --> 00:06:45,320 showing the insect exactly where to land and which way to taxi. 76 00:06:45,320 --> 00:06:49,480 Many insects can see parts of the spectrum that are invisible to us, 77 00:06:49,480 --> 00:06:50,920 such as ultraviolet. 78 00:06:50,920 --> 00:06:55,240 So if we photograph a flower with film sensitive to ultraviolet light, 79 00:06:55,240 --> 00:06:59,840 we can get an insect-eye view of it, which is sometimes very different. 80 00:07:01,000 --> 00:07:02,760 This meadow cranesbill 81 00:07:02,760 --> 00:07:05,640 seems to have faint lines on its petals, 82 00:07:05,640 --> 00:07:09,920 but their ultraviolet markings are very distinct indeed. 83 00:07:13,720 --> 00:07:16,600 Other plants have adopted a different tactic. 84 00:07:16,600 --> 00:07:19,960 Instead of producing pollen in one place on a big flower, 85 00:07:19,960 --> 00:07:24,080 they produce many tiny flowers in a showy bunch, 86 00:07:24,080 --> 00:07:26,240 so that wherever visiting insects go, 87 00:07:26,240 --> 00:07:28,600 there is pollen and nectar to be gathered. 88 00:07:36,280 --> 00:07:38,600 Some have taken this design so far, 89 00:07:38,600 --> 00:07:41,800 that they have come to look like single flowers. 90 00:07:41,800 --> 00:07:46,240 The yellow mass in the centre of this daisy is made up of several hundred 91 00:07:46,240 --> 00:07:50,160 small flowers, each with its stamens and ovaries. 92 00:07:51,160 --> 00:07:54,680 So it is to insects and their sensitive eyes 93 00:07:54,680 --> 00:07:56,880 that we owe so much beauty. 94 00:07:56,880 --> 00:08:01,200 But there are many drab flowers - the hazel, for example. 95 00:08:01,200 --> 00:08:04,360 It's obvious these must rely on a quite different way 96 00:08:04,360 --> 00:08:06,480 of transporting pollen - the wind. 97 00:08:06,480 --> 00:08:10,840 The male flowers have to be large to produce the great quantities 98 00:08:10,840 --> 00:08:13,920 of pollen needed for such a haphazard method. 99 00:08:13,920 --> 00:08:16,720 But the female flower, with no need to advertise, 100 00:08:16,720 --> 00:08:19,240 is an inconspicuous little tuft. 101 00:08:21,880 --> 00:08:25,240 Oak trees use a similar system 102 00:08:25,240 --> 00:08:28,520 with separate male flowers that fill the atmosphere with pollen, 103 00:08:28,520 --> 00:08:31,960 only a tiny proportion of which rains down onto the place where it 104 00:08:31,960 --> 00:08:35,280 serves its most proper purpose - on the female flower. 105 00:08:37,200 --> 00:08:42,760 Some flowers use wind in a different way, to summon insects with perfume. 106 00:08:42,760 --> 00:08:48,320 The arum lily's intoxicating scent attracts them just as it pleases us. 107 00:08:48,320 --> 00:08:51,680 But some insects have different tastes from ours. 108 00:08:52,920 --> 00:08:56,480 The stapelia smells of rotting flesh, 109 00:08:56,480 --> 00:08:59,720 disgusting to us, but extremely attractive to flies 110 00:08:59,720 --> 00:09:01,080 that feed on carrion. 111 00:09:03,280 --> 00:09:04,360 And when they arrive, 112 00:09:04,360 --> 00:09:06,880 they find flowers that tempt them still further, 113 00:09:06,880 --> 00:09:11,320 for their petals actually resemble the wrinkled, decaying skin 114 00:09:11,320 --> 00:09:12,520 of a dead animal. 115 00:09:18,400 --> 00:09:22,280 The amorphophallus of the jungles of the Far East relies 116 00:09:22,280 --> 00:09:24,160 almost entirely on smell. 117 00:09:24,160 --> 00:09:27,880 The overpowering stench that comes from this huge bloom, 118 00:09:27,880 --> 00:09:31,160 as tall as a man, resembles that of rotting fish, 119 00:09:31,160 --> 00:09:33,920 mixed perhaps with a little burnt sugar. 120 00:09:33,920 --> 00:09:37,360 Its European relative, the modest wild arum or cuckoo pint 121 00:09:37,360 --> 00:09:40,760 of English hedgerows, also produces a faint, 122 00:09:40,760 --> 00:09:43,520 unpleasant smell as well as warmth. 123 00:09:43,520 --> 00:09:47,680 Having attracted numerous small flies, it then traps them. 124 00:09:47,680 --> 00:09:52,120 The lower part of the scent-producing rod secretes little drops of oil. 125 00:09:52,120 --> 00:09:56,440 Insect visitors lose their foothold and tumble past the slippery, 126 00:09:56,440 --> 00:10:00,560 downward-pointing hairs into the lower chamber, where the flowers are. 127 00:10:02,640 --> 00:10:05,240 The top ones are male, which are not yet mature. 128 00:10:05,240 --> 00:10:07,600 There's nothing here for the insects. 129 00:10:16,320 --> 00:10:20,000 Below the male flowers are the female flowers. 130 00:10:22,560 --> 00:10:26,640 The small flies, which may have visited other arums the previous day, 131 00:10:26,640 --> 00:10:29,800 now inadvertently spread pollen on them. 132 00:10:29,800 --> 00:10:34,600 But the insects can't escape. The oily hairs keep them imprisoned 133 00:10:34,600 --> 00:10:37,800 and they have to remain there all night. 134 00:10:40,840 --> 00:10:45,240 The next morning, the hairs, the bars of their prison, have shrivelled. 135 00:10:45,240 --> 00:10:49,320 The female flowers have closed their stigmas so they can no longer 136 00:10:49,320 --> 00:10:53,240 be fertilised, and secreted a tiny drop of honey as a reward. 137 00:10:53,240 --> 00:10:57,080 But the male flowers have opened and shed pollen over the flies, 138 00:10:57,080 --> 00:11:00,760 which are now free to look for another arum in which they may, 139 00:11:00,760 --> 00:11:02,840 inadvertently, spend the night. 140 00:11:05,200 --> 00:11:09,000 Pollen taken from one species of flower and deposited on a different 141 00:11:09,000 --> 00:11:11,160 species is wasted. 142 00:11:11,160 --> 00:11:14,680 So there's been a tendency in the insect-flower alliance 143 00:11:14,680 --> 00:11:17,200 for particular partnerships to develop 144 00:11:17,200 --> 00:11:21,360 and for one species of flower to become intimately involved 145 00:11:21,360 --> 00:11:23,640 with just one species of insect. 146 00:11:23,640 --> 00:11:26,520 The nectar of some flowers is hidden away and reserved 147 00:11:26,520 --> 00:11:30,360 for those insects with exactly the right mouth parts and feeding 148 00:11:30,360 --> 00:11:34,720 manners, and which will assiduously visit all the blooms of that species 149 00:11:34,720 --> 00:11:37,480 that they can manage during the flowering season. 150 00:11:38,760 --> 00:11:42,240 The salvia blossom only opens its doors when an insect 151 00:11:42,240 --> 00:11:46,880 of the particular weight and shape of a bee lands on its flight deck, 152 00:11:46,880 --> 00:11:51,440 triggering the stamens to stamp pollen on top of its abdomen. 153 00:12:02,760 --> 00:12:05,480 The flowers go on producing nectar, 154 00:12:05,480 --> 00:12:09,240 and a few days later their ovaries become mature. 155 00:12:11,320 --> 00:12:13,720 When a bee comes to visit them this time, 156 00:12:13,720 --> 00:12:16,920 it's the stigma projecting from the top of the ovary 157 00:12:16,920 --> 00:12:20,320 that jerks downwards and collects the pollen. 158 00:12:26,680 --> 00:12:30,440 This kind of relationship has led flowers away from the original 159 00:12:30,440 --> 00:12:32,440 circular designs like magnolias 160 00:12:32,440 --> 00:12:36,520 to develop complicated constructions of triggers and levers, 161 00:12:36,520 --> 00:12:40,160 delicately balanced platforms and slippery pits. 162 00:12:40,160 --> 00:12:43,360 The bloom has now become a kind of obstacle course, 163 00:12:43,360 --> 00:12:46,240 ensuring that the visitors are not able to collect their rewards 164 00:12:46,240 --> 00:12:51,520 without completing the essential service of transporting the pollen. 165 00:12:51,520 --> 00:12:55,840 The most complicated mechanisms of all are those produced by orchids. 166 00:12:55,840 --> 00:12:59,520 Even now, there are some we don't understand. 167 00:13:03,520 --> 00:13:06,680 This one, the flying duck orchid from Australia, 168 00:13:06,680 --> 00:13:09,720 has the most extraordinary action as it opens, 169 00:13:09,720 --> 00:13:14,040 but we don't know why it's shaped this way, why it moves like this 170 00:13:14,040 --> 00:13:17,800 or on what insect it relies to carry its pollen. 171 00:13:17,800 --> 00:13:21,640 This orchid attracts insects by sexual impersonation. 172 00:13:21,640 --> 00:13:25,680 It gives off a perfume like that of a female ichneumon wasp. 173 00:13:25,680 --> 00:13:28,880 When the male arrives, he finds something that not only smells 174 00:13:28,880 --> 00:13:31,480 like his female, but looks remarkably like her. 175 00:13:33,520 --> 00:13:37,040 At one end of the bloom, there's a mass of pollen stuck together 176 00:13:37,040 --> 00:13:38,600 into a horseshoe shape. 177 00:13:39,880 --> 00:13:42,680 The ichneumon male copulates with the flower. 178 00:13:49,800 --> 00:13:55,160 And the pollen mass is so placed that it fastens neatly onto his abdomen. 179 00:13:55,160 --> 00:13:58,400 In fact, this orchid is totally dependent on one species 180 00:13:58,400 --> 00:14:02,360 of ichneumon wasp for pollination and therefore reproduction. 181 00:14:02,360 --> 00:14:06,960 The orchid can only survive as long as the ichneumon wasps do. 182 00:14:21,080 --> 00:14:24,640 When the male insect copulates with the next flower, 183 00:14:24,640 --> 00:14:27,200 he delivers the pollen from the last. 184 00:14:39,440 --> 00:14:44,120 The yucca plant of Central America has a relationship with its insect 185 00:14:44,120 --> 00:14:48,760 partner that is so close that now both insect and plant are completely 186 00:14:48,760 --> 00:14:50,560 dependent on one another. 187 00:14:54,400 --> 00:14:59,240 The yucca's creamy blossoms are visited by tiny moths. 188 00:14:59,240 --> 00:15:03,600 During the day, the moths spend a lot of time moving from flower to flower 189 00:15:03,600 --> 00:15:05,000 and inspecting them. 190 00:15:05,000 --> 00:15:07,400 All are not at the same stage of development. 191 00:15:07,400 --> 00:15:11,560 The stamens become mature first and split open, and it's these 192 00:15:11,560 --> 00:15:13,120 that the moth is looking for. 193 00:15:15,920 --> 00:15:19,760 In the late afternoon, the female moth, having already mated, 194 00:15:19,760 --> 00:15:22,800 is collecting pollen from suitable flowers. 195 00:15:36,640 --> 00:15:39,520 She's now gathered the pollen into a tight ball 196 00:15:39,520 --> 00:15:41,920 which she holds under her head as she searches 197 00:15:41,920 --> 00:15:46,280 for other flowers which are in a different state of development. 198 00:15:51,120 --> 00:15:55,400 This time, she's more interested in the central part of the flower, 199 00:15:55,400 --> 00:15:59,200 and takes up a position alongside one of the ovaries, which have 200 00:15:59,200 --> 00:16:04,120 a green-tipped stigma. Here she will stay for about 20 minutes. 201 00:16:04,120 --> 00:16:08,720 Her egg-laying tube is deep at the bottom of the flower's ovary, 202 00:16:08,720 --> 00:16:11,720 and she's laying her own eggs there. 203 00:16:15,440 --> 00:16:18,600 Having finished laying, she separates some pollen grains 204 00:16:18,600 --> 00:16:22,320 from the ball she's collected and smears them into the stigma 205 00:16:22,320 --> 00:16:25,680 with mouth parts specially developed for the purpose. 206 00:16:44,840 --> 00:16:47,720 Now she will repeat the entire procedure 207 00:16:47,720 --> 00:16:49,960 in other ovaries of the flower. 208 00:16:59,240 --> 00:17:01,480 The egg-laying position again. 209 00:17:11,560 --> 00:17:14,440 Again she will pollinate the flower. 210 00:17:16,120 --> 00:17:20,520 First she removes a small amount of pollen from the ball she's holding. 211 00:17:24,280 --> 00:17:26,080 By pollinating the flower, 212 00:17:26,080 --> 00:17:30,680 she serves not only the yucca but her own offspring, for she ensures the 213 00:17:30,680 --> 00:17:35,280 eggs in the ovary below will develop so that her caterpillars when they 214 00:17:35,280 --> 00:17:39,080 hatch will have a rich source of food immediately to hand. 215 00:17:40,520 --> 00:17:44,840 But the caterpillars won't eat all the seeds. The moths don't lay as 216 00:17:44,840 --> 00:17:49,080 many eggs as that, so when the yucca comes into fruit, there are plenty 217 00:17:49,080 --> 00:17:53,000 of undamaged seeds to ensure that new plants will appear. 218 00:17:53,000 --> 00:17:56,760 But the balance is a very delicate one - if it went wrong, 219 00:17:56,760 --> 00:18:00,200 it could be disastrous for both plants and insect. 220 00:18:00,200 --> 00:18:03,080 Without the moth, the yucca would not be pollinated. 221 00:18:03,080 --> 00:18:06,600 Nothing else has those specially modified mouth parts for pressing 222 00:18:06,600 --> 00:18:08,200 the pollen into the style. 223 00:18:08,200 --> 00:18:12,600 And without the yucca, the moth's caterpillars would starve. 224 00:18:14,440 --> 00:18:17,160 The seductive odours and beguiling shapes of flowers 225 00:18:17,160 --> 00:18:20,200 are so attractive to the insects for whom they're designed 226 00:18:20,200 --> 00:18:23,200 that they find them virtually irresistible. 227 00:18:23,200 --> 00:18:27,720 Other insects turn that to their advantage in a different way. 228 00:18:32,160 --> 00:18:36,160 This ginger flower has petals that move. 229 00:18:37,440 --> 00:18:42,120 It's one of the most extravagant designs of any insect, for this, 230 00:18:42,120 --> 00:18:47,200 with flaps on its legs that match the petals of the flower, is a mantis. 231 00:19:15,600 --> 00:19:18,320 The butterfly comes to sip nectar. 232 00:19:42,120 --> 00:19:47,040 There are many different kinds of mantis, all marvellously camouflaged, 233 00:19:47,040 --> 00:19:49,080 all voracious hunters. 234 00:19:50,400 --> 00:19:52,680 The flesh of an insect is succulent, 235 00:19:52,680 --> 00:19:56,480 but to get at it the mantis has to deal with the external skeleton, 236 00:19:56,480 --> 00:19:58,400 the shell of chitin. 237 00:19:58,400 --> 00:20:02,680 Chitin is dead material. It won't expand. It's one of the few 238 00:20:02,680 --> 00:20:07,240 limitations to the insect body that is otherwise so versatile. 239 00:20:07,240 --> 00:20:11,560 In order to grow, all insects have to shed their skin at regular intervals, 240 00:20:11,560 --> 00:20:14,880 and this bug is just about to do so. 241 00:20:14,880 --> 00:20:19,760 A new, soft skin has formed underneath, and by sucking in air 242 00:20:19,760 --> 00:20:24,280 and inflating itself, the bug is cracking its old skin. 243 00:20:55,320 --> 00:20:59,160 Once free, the bug inflates itself still further, 244 00:20:59,160 --> 00:21:04,160 stretching out the crinkles in its soft skin and expanding. 245 00:21:04,160 --> 00:21:07,960 After an hour or so, its new skeleton has hardened. 246 00:21:13,360 --> 00:21:17,760 A spiny leaf insect is just about to do the same trick. 247 00:21:56,000 --> 00:21:59,120 Its old shell hangs from the branch above it 248 00:21:59,120 --> 00:22:01,600 like the ghost of its former self. 249 00:22:06,440 --> 00:22:08,840 But the more complicated an insect's body, 250 00:22:08,840 --> 00:22:13,160 the more laborious and difficult this process of skin shedding becomes. 251 00:22:13,160 --> 00:22:18,440 And some insects not only simplify it but exploit different food sources 252 00:22:18,440 --> 00:22:20,840 by leading split lives. 253 00:22:20,840 --> 00:22:25,160 This creature emerging from the egg will eventually become a butterfly. 254 00:22:25,160 --> 00:22:29,480 But for the first part of its life, it will keep its body simple. 255 00:22:29,480 --> 00:22:31,400 A caterpillar. 256 00:22:31,400 --> 00:22:35,000 A caterpillar is little more than an eating machine. 257 00:22:35,000 --> 00:22:39,920 This one starts its life as it means to go on by eating its own eggshell. 258 00:22:45,560 --> 00:22:49,880 The caterpillar's existence is totally dedicated to food. 259 00:22:49,880 --> 00:22:53,240 It won't breed, so it doesn't need sexual organs. 260 00:22:53,240 --> 00:22:55,360 It has no cause to attract a mate, 261 00:22:55,360 --> 00:22:58,000 so it need not send out any signals to one 262 00:22:58,000 --> 00:23:01,720 or develop wings so it can fly off and look for one. 263 00:23:01,720 --> 00:23:04,120 Its parents have gone to a great deal of trouble 264 00:23:04,120 --> 00:23:07,840 to ensure it finds ample food immediately to hand, 265 00:23:07,840 --> 00:23:11,280 so all it really needs is an efficient pair of jaws 266 00:23:11,280 --> 00:23:14,760 and, behind them, a bag-like expandable body. 267 00:23:18,920 --> 00:23:22,080 But if a caterpillar's body is to expand, 268 00:23:22,080 --> 00:23:25,160 it can't have a hard, rigid external skeleton. 269 00:23:25,160 --> 00:23:29,000 Just a thin, flexible skin that is easily shed and replaced. 270 00:23:29,000 --> 00:23:31,280 And that could leave it vulnerable. 271 00:23:31,280 --> 00:23:35,720 So caterpillars have to have other ways of protecting themselves. 272 00:23:35,720 --> 00:23:37,080 Some do it by bluff, 273 00:23:37,080 --> 00:23:40,720 developing markings that look like fearsome eyes. 274 00:23:47,680 --> 00:23:51,800 Some rely on camouflage initially, and if that doesn't work, 275 00:23:51,800 --> 00:23:54,680 they too try to startle. 276 00:24:01,520 --> 00:24:03,920 The caterpillar of an Australian swallowtail 277 00:24:03,920 --> 00:24:07,200 looks convincingly like a glistening bird dropping, 278 00:24:07,200 --> 00:24:10,560 and if any predator thinks that's worth investigating, 279 00:24:10,560 --> 00:24:14,400 then it suddenly, and unexpectedly, produces strange antennae. 280 00:24:23,560 --> 00:24:28,120 Many caterpillars sprout long hairs tipped with poison that can cause 281 00:24:28,120 --> 00:24:32,200 quite a rash on a human skin and certainly put off a lot of birds. 282 00:24:32,200 --> 00:24:36,400 To make sure that would-be predators are in no doubt they're unpalatable, 283 00:24:36,400 --> 00:24:40,800 the caterpillars advertise themselves with bright warning colours. 284 00:24:45,440 --> 00:24:48,480 So, with the best protection they can muster, 285 00:24:48,480 --> 00:24:51,840 the caterpillars industriously pack away their food, 286 00:24:51,840 --> 00:24:56,080 slipping off their thin but often flamboyant skins when a bigger one 287 00:24:56,080 --> 00:25:00,480 is required until they have grown as much as they need, and then they 288 00:25:00,480 --> 00:25:04,680 prepare for the first of two highly dramatic transformations. 289 00:25:14,920 --> 00:25:19,360 Many moths make the change in private behind a silken shroud. 290 00:25:19,360 --> 00:25:22,720 Industriously, they spin and weave. 291 00:25:42,120 --> 00:25:46,120 This one adds tiny pieces of bark to camouflage the cocoon. 292 00:25:51,920 --> 00:25:55,600 Some of those that had poisonous bristles shed them in their 293 00:25:55,600 --> 00:26:00,320 final moult within their cocoons and weave them into their wrappings 294 00:26:00,320 --> 00:26:02,800 so that they will continue to protect them. 295 00:26:35,120 --> 00:26:37,520 And now, all seems still. 296 00:26:37,520 --> 00:26:40,880 Life, apparently, is suspended. 297 00:26:40,880 --> 00:26:44,240 But inside, a profound revolution is taking place. 298 00:26:44,240 --> 00:26:48,040 The caterpillar's body is breaking down into a kind of soup. 299 00:26:48,040 --> 00:26:52,120 Clusters of cells that have remained dormant since the creature emerged 300 00:26:52,120 --> 00:26:56,640 from the egg now become active, absorbing the soup, multiplying 301 00:26:56,640 --> 00:27:01,560 and reassembling a new body from all the material that the caterpillar 302 00:27:01,560 --> 00:27:03,640 so industriously gathered. 303 00:27:03,640 --> 00:27:08,440 Most butterfly caterpillars embark on this change unscreened by a cocoon, 304 00:27:08,440 --> 00:27:13,520 though usually inconspicuously close to a stem or under a leaf. 305 00:27:13,520 --> 00:27:16,960 The Australian common crow caterpillar first spins 306 00:27:16,960 --> 00:27:19,280 a silk thread, from which it hangs. 307 00:27:23,560 --> 00:27:27,440 Beneath its skin it has secreted a new and different one. 308 00:27:27,440 --> 00:27:29,760 The old skin splits and rolls off, 309 00:27:29,760 --> 00:27:33,520 taking with it the hard parts for which there's no more use, 310 00:27:33,520 --> 00:27:38,200 the tiny claws from the legs and those hard-worked jaws. 311 00:27:47,480 --> 00:27:51,800 The new skin hardens and in a few hours becomes mirror-like, 312 00:27:51,800 --> 00:27:55,320 reflecting the foliage around it for better camouflage. 313 00:27:59,160 --> 00:28:02,680 The body of a butterfly may take months to rebuild, 314 00:28:02,680 --> 00:28:04,840 or as little as a week. 315 00:28:22,200 --> 00:28:27,000 The wings are crumpled bags, but the insect pumps blood into them 316 00:28:27,000 --> 00:28:29,360 and slowly they expand. 317 00:28:38,200 --> 00:28:42,640 The wings dry and harden, and the Australian orchard butterfly 318 00:28:42,640 --> 00:28:44,440 is ready for flight. 319 00:28:47,280 --> 00:28:52,040 The primary task now of all these butterflies is to find a mate. 320 00:28:53,920 --> 00:28:57,040 Scent is used to locate their mates over long distances, 321 00:28:57,040 --> 00:29:00,480 and now their gorgeous wings carry them on the search, 322 00:29:00,480 --> 00:29:04,720 proclaiming with their colours and patterns their identities 323 00:29:04,720 --> 00:29:08,520 and so attracting mates of the same species at close range. 324 00:29:08,520 --> 00:29:11,880 They still feed on nectar to provide them with the energy to fly, 325 00:29:11,880 --> 00:29:15,960 but they don't need any food to build or renew their tissues. 326 00:29:15,960 --> 00:29:18,320 The time for growth is over. 327 00:29:37,800 --> 00:29:40,760 The birdwing butterflies of the Far East 328 00:29:40,760 --> 00:29:43,720 are among the largest and most graceful of butterflies. 329 00:30:17,200 --> 00:30:21,760 Male and female butterflies meet and courtship begins. 330 00:30:36,040 --> 00:30:40,240 Successful males couple with females by joining abdomens. 331 00:30:59,080 --> 00:31:04,080 These marvellous, elaborate structures, the wings, each clothed 332 00:31:04,080 --> 00:31:09,280 by thousands of microscopic scales arranged in intricate patterns, 333 00:31:09,280 --> 00:31:13,600 have, within a few days - in some species within a few hours - 334 00:31:13,600 --> 00:31:15,520 completed their purpose. 335 00:31:15,520 --> 00:31:18,320 Male and female have found one another 336 00:31:18,320 --> 00:31:20,640 and the cycle will begin again. 337 00:31:22,040 --> 00:31:29,080 The atlas moth is one of the biggest of all butterflies and moths. 338 00:31:30,440 --> 00:31:34,320 But its body, of course, is small compared with that of a bird. 339 00:31:34,320 --> 00:31:38,080 The reason is because of another limitation 340 00:31:38,080 --> 00:31:40,880 to the basic insect body design. 341 00:31:40,880 --> 00:31:46,160 This moth, like all insects, breathes through a series of holes 342 00:31:46,160 --> 00:31:50,480 along its flank. They're the openings of tubes, with many branches, 343 00:31:50,480 --> 00:31:52,400 that extend throughout the body 344 00:31:52,400 --> 00:31:55,760 and carry oxygen to every individual organ. 345 00:31:55,760 --> 00:31:58,640 It's a system that works by diffusion. 346 00:31:58,640 --> 00:32:01,800 It works very well over short distances. 347 00:32:01,800 --> 00:32:06,400 But as the length of the tube increases, it becomes less efficient, 348 00:32:06,400 --> 00:32:09,160 and eventually it becomes impossible. 349 00:32:09,160 --> 00:32:14,520 That's why there are no moths or butterflies the size of eagles. 350 00:32:26,720 --> 00:32:30,400 The insects have, however, found one way of transcending 351 00:32:30,400 --> 00:32:34,400 this problem of the limitation of size - numbers. 352 00:32:34,400 --> 00:32:37,080 In this one single termite hill, 353 00:32:37,080 --> 00:32:41,600 there must live two or three million insects. 354 00:32:41,600 --> 00:32:45,440 But there are good reasons for considering them not as individuals 355 00:32:45,440 --> 00:32:50,720 but as together constituting one single great super-organism. 356 00:32:50,720 --> 00:32:54,560 A super-organism that simply in terms of animal tissue alone 357 00:32:54,560 --> 00:32:58,240 must weigh as much as an antelope and which certainly crops 358 00:32:58,240 --> 00:33:01,760 the surrounding vegetation as heavily as an antelope. 359 00:33:01,760 --> 00:33:04,680 And when you look at these super-organisms 360 00:33:04,680 --> 00:33:06,560 out here in Western Australia, 361 00:33:06,560 --> 00:33:10,400 they seem to dominate the landscape just as powerfully 362 00:33:10,400 --> 00:33:14,480 as antelope dominate the plains of East Africa. 363 00:33:20,000 --> 00:33:24,320 This type of colony is not just a haphazard collection of individuals 364 00:33:24,320 --> 00:33:27,160 who've decided to share the same dwelling, 365 00:33:27,160 --> 00:33:30,600 like human beings in a tower block. For one thing, they're all 366 00:33:30,600 --> 00:33:34,120 one family, all the children of a single gigantic female. 367 00:33:34,120 --> 00:33:37,960 For another, they're all incomplete creatures. 368 00:33:37,960 --> 00:33:40,760 Not one of them could survive by itself for long. 369 00:33:40,760 --> 00:33:43,600 These workers are all sterile. 370 00:33:55,720 --> 00:34:00,400 The soldiers, which defend the community, have such huge jaws 371 00:34:00,400 --> 00:34:03,120 that they can't feed themselves. 372 00:34:03,120 --> 00:34:06,960 And the queen, in the middle of the colony, is so huge 373 00:34:06,960 --> 00:34:10,800 that she can't move and has to have food brought to her. 374 00:34:10,800 --> 00:34:13,200 She's a gigantic egg machine. 375 00:34:13,200 --> 00:34:17,040 The workers bring food to one end and collect eggs from the other 376 00:34:17,040 --> 00:34:22,240 which she produces at the almost unbelievable rate of 30,000 a day. 377 00:34:22,240 --> 00:34:26,160 The male, the size of a wasp, lies alongside her. 378 00:34:26,160 --> 00:34:29,520 She has a controlling effect on the activity of the colony. 379 00:34:29,520 --> 00:34:33,600 She sweats a chemical substance which the workers obtain by 380 00:34:33,600 --> 00:34:38,040 licking her body, and this in effect gives them their instructions. 381 00:34:38,040 --> 00:34:40,280 It stimulates them to do certain things - 382 00:34:40,280 --> 00:34:43,400 to feed the young grubs on a particular diet, 383 00:34:43,400 --> 00:34:46,080 to move the eggs into special places. 384 00:34:48,800 --> 00:34:52,640 At one moment, either because of a change in the queen's instructions 385 00:34:52,640 --> 00:34:55,040 or because the eggs she lays are slightly different, 386 00:34:55,040 --> 00:35:00,480 they hatch not into sterile workers but into sexually mature adults, 387 00:35:00,480 --> 00:35:02,920 both male and female. 388 00:35:04,800 --> 00:35:10,360 And then, suddenly, the colony seems to smoke as thousands upon thousands 389 00:35:10,360 --> 00:35:15,800 of individuals emerge to fly off and colonise the surrounding country. 390 00:35:37,120 --> 00:35:41,920 When they land, their wings break off. They won't be needed again. 391 00:35:41,920 --> 00:35:46,120 Now the male and female begin their courtship dances. 392 00:35:58,240 --> 00:35:59,800 Once they've paired, 393 00:35:59,800 --> 00:36:03,840 they find a crevice and start to build themselves a nest. 394 00:36:03,840 --> 00:36:06,680 He fertilises her, she will lay eggs, 395 00:36:06,680 --> 00:36:10,080 and so together they will found a new colony. 396 00:36:10,080 --> 00:36:13,920 A new royal egg machine will go into full production 397 00:36:13,920 --> 00:36:17,640 and the various castes of individuals will hatch and grow. 398 00:36:23,760 --> 00:36:27,720 Highly organised social behaviour like this seems to have evolved 399 00:36:27,720 --> 00:36:31,880 several times among insects - once among termites, related to 400 00:36:31,880 --> 00:36:36,240 cockroaches, and several times among the ants, bees and wasps. 401 00:36:36,240 --> 00:36:38,280 All three groups have mouth parts 402 00:36:38,280 --> 00:36:41,400 adapted for chewing so they can easily build nests. 403 00:36:46,080 --> 00:36:50,360 The wasps also use theirs for manipulating prey. 404 00:36:55,200 --> 00:36:58,120 Having paralysed their prey with a sting, 405 00:36:58,120 --> 00:37:01,240 some wasps pack them into their cells with the eggs 406 00:37:01,240 --> 00:37:03,960 so their young will have fresh meat when they hatch. 407 00:37:05,320 --> 00:37:07,720 Not all wasps and bees are social. 408 00:37:07,720 --> 00:37:09,480 Many of them are solitary, 409 00:37:09,480 --> 00:37:12,360 digging and stocking only their own cells. 410 00:37:14,120 --> 00:37:17,960 Sometimes, however, the scarcity of suitable nesting places 411 00:37:17,960 --> 00:37:22,360 causes otherwise solitary bees to breed close to one another. 412 00:37:25,720 --> 00:37:28,920 When the adult bees of this species emerge from their pupae, 413 00:37:28,920 --> 00:37:32,880 the males fight one another in order to mate with the females. 414 00:37:41,600 --> 00:37:44,800 Other species of bee that nest in similar sites 415 00:37:44,800 --> 00:37:47,200 are little more socially inclined. 416 00:37:47,200 --> 00:37:50,960 By this Kansas river, a group of little sweat bees are nesting 417 00:37:50,960 --> 00:37:53,160 in a burrow with one entrance hole. 418 00:37:54,160 --> 00:37:57,320 A guard bee stands like a sentry at the entrance 419 00:37:57,320 --> 00:38:00,120 and allows only its own species to enter. 420 00:38:01,920 --> 00:38:04,600 New arrivals appear to be instructed what to do 421 00:38:04,600 --> 00:38:06,720 by the bee that is moving backwards. 422 00:38:06,720 --> 00:38:11,120 She appears to be the dominant bee in the small colony. 423 00:38:11,120 --> 00:38:14,120 Other bees that seem to be identical in form 424 00:38:14,120 --> 00:38:16,880 apparently accept subordinate roles, 425 00:38:16,880 --> 00:38:20,800 taking on such jobs as building new chambers. 426 00:38:20,800 --> 00:38:22,720 Other chambers are complete. 427 00:38:22,720 --> 00:38:26,600 They already contain eggs or larvae at various stages of development, 428 00:38:26,600 --> 00:38:29,680 together with a ball of pollen for food. 429 00:38:35,160 --> 00:38:37,000 While all the work goes on, 430 00:38:37,000 --> 00:38:40,360 one dominant bee appears to control the group's activities. 431 00:38:40,360 --> 00:38:44,200 This bee can probably recognise others by their smell. 432 00:38:44,200 --> 00:38:48,000 Certainly, taste and smell play a vital part in the coordination 433 00:38:48,000 --> 00:38:50,520 of really big and complex insect colonies 434 00:38:50,520 --> 00:38:53,080 like those of the honey bee. 435 00:38:57,720 --> 00:39:01,720 Workers here are continually collecting chemical substances 436 00:39:01,720 --> 00:39:05,360 from the queen. She is the particularly large insect here 437 00:39:05,360 --> 00:39:08,800 inspecting new cells before depositing eggs in them. 438 00:39:14,840 --> 00:39:19,640 The chemical messages she produces circulate throughout the colony 439 00:39:19,640 --> 00:39:23,120 because of the workers' habit of exchanging spittle. 440 00:39:24,880 --> 00:39:29,200 Unlike termites, who travel over land to find food, bees fly. 441 00:39:29,200 --> 00:39:32,520 So they're unable to lay a scent trail on the ground. 442 00:39:32,520 --> 00:39:35,880 Bees have had to evolve a different method of telling co-workers 443 00:39:35,880 --> 00:39:37,680 where the food is. 444 00:39:39,320 --> 00:39:43,160 When a worker returns from a new, rich source of food, 445 00:39:43,160 --> 00:39:45,360 it goes onto the vertical cones, 446 00:39:45,360 --> 00:39:48,400 its satchels on its legs packed with yellow pollen. 447 00:39:51,080 --> 00:39:54,480 After exchanging spittle, it dances. 448 00:39:54,480 --> 00:39:59,040 That waggling dance is about 20 degrees to the left of vertical, 449 00:39:59,040 --> 00:40:03,280 and that means that the flower she's discovered can be found by flying 450 00:40:03,280 --> 00:40:05,640 about 20 degrees to the left of the sun. 451 00:40:12,480 --> 00:40:16,080 The other workers "read" the dance, which is accompanied by noises 452 00:40:16,080 --> 00:40:18,880 which some people believe also carry information. 453 00:40:22,800 --> 00:40:27,040 On leaving the hive, the workers remember the angle of the dance 454 00:40:27,040 --> 00:40:30,880 and set off at the same angle to the left of the sun. 455 00:40:30,880 --> 00:40:33,200 Because they can see polarised light, 456 00:40:33,200 --> 00:40:36,360 the bees don't even have to wait for a cloudless day. 457 00:40:39,320 --> 00:40:44,120 The origin of these colonies of insects presents quite a puzzle. 458 00:40:44,120 --> 00:40:47,480 It's a basic principle of evolution by natural selection 459 00:40:47,480 --> 00:40:51,320 that individual animals are engaged in a struggle 460 00:40:51,320 --> 00:40:56,120 to survive, to breed and pass on their genes to the next generation. 461 00:40:56,120 --> 00:41:00,440 How could it have been, then, that in the past there was some insect 462 00:41:00,440 --> 00:41:06,200 that actually gave up that right and laboured to help another insect 463 00:41:06,200 --> 00:41:10,040 pass on her genes to the next generation? 464 00:41:10,040 --> 00:41:13,080 The answer seems to lie in the particular way 465 00:41:13,080 --> 00:41:16,200 that these insects reproduce. 466 00:41:16,200 --> 00:41:18,160 Before the queen began laying, 467 00:41:18,160 --> 00:41:21,480 she was fertilised by several males called drones. 468 00:41:21,480 --> 00:41:23,720 She stored their sperm in her body, 469 00:41:23,720 --> 00:41:26,880 but withheld it when laying to produce males 470 00:41:26,880 --> 00:41:29,560 so they would carry only her genes. 471 00:41:32,160 --> 00:41:36,760 When she lays in cells to produce female workers, she fertilises 472 00:41:36,760 --> 00:41:39,200 the eggs by releasing some sperm. 473 00:41:39,200 --> 00:41:42,760 Occasionally, one of these females is allowed to develop into 474 00:41:42,760 --> 00:41:47,440 a new queen, and eventually the old queen will leave in a swarm with her 475 00:41:47,440 --> 00:41:50,000 sister workers to start a new colony. 476 00:41:50,000 --> 00:41:52,400 The net result of this complicated system 477 00:41:52,400 --> 00:41:56,240 is that the female workers and their nieces by their new sister queen 478 00:41:56,240 --> 00:41:58,160 are unusually closely related. 479 00:41:58,160 --> 00:42:02,400 In other words, they share a high proportion of common genes. 480 00:42:05,640 --> 00:42:09,760 And so, when these sterile workers labour away for the benefit 481 00:42:09,760 --> 00:42:13,320 of a colony, in order to help the queen pass on her genes 482 00:42:13,320 --> 00:42:17,440 to the next generation, they are in fact labouring on behalf of 483 00:42:17,440 --> 00:42:21,240 their own genes. The insects that have brought this 484 00:42:21,240 --> 00:42:24,800 to a particularly high level are the ants. 485 00:42:26,320 --> 00:42:30,200 Their similar methods of reproduction and skill at manipulation 486 00:42:30,200 --> 00:42:36,000 seems to be the reason why they too have evolved amazing social systems. 487 00:42:36,000 --> 00:42:38,120 The green tree ants of Southeast Asia 488 00:42:38,120 --> 00:42:40,800 cooperate in a most complex way to build their nests. 489 00:42:40,800 --> 00:42:45,000 Groups of workers hold two leaves together, gripping them 490 00:42:45,000 --> 00:42:48,280 with their legs and jaws to form a living bond. 491 00:42:50,960 --> 00:42:54,320 Other workers bring the young grubs from the centre of the nest, 492 00:42:54,320 --> 00:42:59,120 and by giving them little squeezes, stimulate them to produce silk. 493 00:42:59,120 --> 00:43:01,560 Then, using them like tubes of glue, 494 00:43:01,560 --> 00:43:04,400 they move them back and forth between the two leaves 495 00:43:04,400 --> 00:43:07,760 until they fasten them together with a sheet of silk. 496 00:43:18,960 --> 00:43:23,240 The cooperative behaviour of the ants holding the leaf starts usually with 497 00:43:23,240 --> 00:43:27,240 one isolated individual who succeeds in bending over part of the leaf, 498 00:43:27,240 --> 00:43:30,120 usually near the tip, where it's easy. 499 00:43:30,120 --> 00:43:33,600 This seems to act as a signal for other ants to join in, 500 00:43:33,600 --> 00:43:36,520 leaving whatever other tasks they're engaged in. 501 00:43:50,680 --> 00:43:53,280 In these ants, the workers are divided 502 00:43:53,280 --> 00:43:55,480 into a major and a minor caste. 503 00:43:55,480 --> 00:43:58,840 The major castes consists of workers who go out and do the foraging 504 00:43:58,840 --> 00:44:02,920 and the minor castes are employed as nurses, looking after the larvae. 505 00:44:09,080 --> 00:44:13,760 In South America, the parasol ants strip trees of their leaves, 506 00:44:13,760 --> 00:44:17,160 cutting them up into pieces and carrying them one by one 507 00:44:17,160 --> 00:44:20,040 into their vast underground nests. 508 00:44:20,040 --> 00:44:22,040 The work goes on night and day, 509 00:44:22,040 --> 00:44:25,960 hundreds of thousands of ants swarming all over the trees. 510 00:44:48,800 --> 00:44:52,920 The technique of carrying a leaf many times bigger than the ant itself 511 00:44:52,920 --> 00:44:56,120 depends on the worker tucking its head down onto its thorax 512 00:44:56,120 --> 00:44:57,880 before taking a grip. 513 00:45:21,960 --> 00:45:27,960 Sometimes they carry these segments for 100 yards, along trails that have 514 00:45:27,960 --> 00:45:32,000 been worn smooth by millions of tiny footsteps, day after day. 515 00:45:36,640 --> 00:45:40,720 The ants will not eat these leaves. They can't - unlike termites, 516 00:45:40,720 --> 00:45:43,880 which have single-celled organisms in their guts 517 00:45:43,880 --> 00:45:46,120 to enable them to digest cellulose. 518 00:45:46,120 --> 00:45:49,040 The ants are collecting leaves in order to chew them up 519 00:45:49,040 --> 00:45:50,520 and make a kind of compost. 520 00:45:50,520 --> 00:45:54,880 On that, they cultivate a fungus in their underground galleries. 521 00:45:56,800 --> 00:46:00,240 The fungus supplies the ants with special juicy branches 522 00:46:00,240 --> 00:46:03,720 for their food, and the ants garden it with their own faeces 523 00:46:03,720 --> 00:46:06,800 and a special antibiotic dressing for a good yield. 524 00:46:09,120 --> 00:46:14,000 The ants have regular refuse tips on the surface, not far from the nest. 525 00:46:20,720 --> 00:46:24,840 Every now and then, the workers will suddenly stop dismantling trees 526 00:46:24,840 --> 00:46:28,120 and turn their attention to cleaning out the nest. 527 00:46:59,600 --> 00:47:03,920 The fungus which the parasol ants grow can survive nowhere else. 528 00:47:03,920 --> 00:47:07,120 They are utterly dependent on one another. 529 00:47:08,440 --> 00:47:11,520 Other ants have similar relationships with trees, 530 00:47:11,520 --> 00:47:15,840 with the trees actually encouraging the ants to take up residence. 531 00:47:15,840 --> 00:47:20,920 Some acacia trees in Central America have thorns for defence. 532 00:47:20,920 --> 00:47:24,200 But these needle-sharp thorns are doubly dangerous 533 00:47:24,200 --> 00:47:29,320 because inside them live colonies of aggressive stinging ants. 534 00:47:33,440 --> 00:47:37,560 Each pair of thorns has an entrance hole near the tip of one of them. 535 00:47:37,560 --> 00:47:40,920 The spongy cells that once filled the thorns 536 00:47:40,920 --> 00:47:44,280 have been chewed away to make a strong and safe brood chamber 537 00:47:44,280 --> 00:47:47,840 that becomes crammed with eggs and developing larvae. 538 00:47:57,320 --> 00:48:00,200 The ants never have to leave the tree to feed, 539 00:48:00,200 --> 00:48:05,000 for the acacia provides the colony with a beautifully balanced diet. 540 00:48:05,000 --> 00:48:09,360 The tiny reddish-brown beads on the leaflet tips are rich in fats, 541 00:48:09,360 --> 00:48:13,440 proteins and vitamins - ideal food for developing insects, 542 00:48:13,440 --> 00:48:16,760 although they have no real function for the tree. 543 00:48:16,760 --> 00:48:21,480 The beads develop on the new leaves and at the tips of the shoots, 544 00:48:21,480 --> 00:48:24,600 so the attendant ants are in a perfect position to protect 545 00:48:24,600 --> 00:48:26,720 the most vulnerable part of the plant. 546 00:48:41,480 --> 00:48:43,640 The acacia also has nectaries, 547 00:48:43,640 --> 00:48:46,280 but these are not part of its flowers. 548 00:48:46,280 --> 00:48:49,880 The nectaries are situated at the base of the leaves, 549 00:48:49,880 --> 00:48:53,280 and the sole function is to provide the ants with the sugary liquid 550 00:48:53,280 --> 00:48:55,080 of which they're extremely fond. 551 00:48:59,480 --> 00:49:03,760 What, then, does the acacia get in return for these services? 552 00:49:03,760 --> 00:49:08,080 The answer is defence. The ants are particularly ferocious 553 00:49:08,080 --> 00:49:11,800 and defend the tree against any other insects that come to feed on it. 554 00:49:11,800 --> 00:49:16,680 What's more, they also drive off any grazing animal that tries to eat 555 00:49:16,680 --> 00:49:20,360 the foliage, and even mutilate and kill climbing vines 556 00:49:20,360 --> 00:49:22,880 that try to cover the host tree. 557 00:49:22,880 --> 00:49:26,720 As a result, in tropical areas where competition is intense, 558 00:49:26,720 --> 00:49:31,040 the acacia trees and their ants are a particularly successful team. 559 00:49:36,400 --> 00:49:40,240 The most aggressive ants of all are the army ants 560 00:49:40,240 --> 00:49:43,120 that build no permanent nest at all. 561 00:49:43,120 --> 00:49:47,920 They also have one of the most advanced societies of all insects. 562 00:49:52,720 --> 00:49:56,560 This colony has been temporarily camped overnight. 563 00:49:56,560 --> 00:50:00,280 Somewhere in the middle of this living ball is the queen 564 00:50:00,280 --> 00:50:04,240 and immature ants protected by the bodies of the workers. 565 00:50:04,240 --> 00:50:07,960 They make their own bivouac by linking their legs and bodies 566 00:50:07,960 --> 00:50:10,840 together with strong tiny claws. 567 00:50:19,120 --> 00:50:23,440 At first light, in the morning, the colony will begin to disperse. 568 00:50:23,440 --> 00:50:28,520 Between 150,000 and 170,000 workers may be present, and some of them must 569 00:50:28,520 --> 00:50:32,640 carry the queen and larvae as the column moves off on a foray 570 00:50:32,640 --> 00:50:37,080 guarded by the huge soldiers, whose only job is defence. 571 00:50:38,800 --> 00:50:43,480 For two or three weeks, the army ants make a new bivouac each night. 572 00:50:43,480 --> 00:50:47,680 Then their behaviour will change and they will make a semi-permanent home, 573 00:50:47,680 --> 00:50:50,040 often in a hollow tree. 574 00:50:53,080 --> 00:50:55,960 The queen is now ready to lay eggs. 575 00:50:55,960 --> 00:50:59,800 Over a few days, protected by her living shelter of workers, 576 00:50:59,800 --> 00:51:03,640 she will lay between 100,000 and 300,000 eggs. 577 00:51:03,640 --> 00:51:06,440 After three weeks, the larvae hatch. 578 00:51:06,440 --> 00:51:10,720 And because of chemical secretions produced by these new recruits, 579 00:51:10,720 --> 00:51:14,560 the colony is once more galvanised into great activity. 580 00:51:18,400 --> 00:51:23,480 Now the nomadic phase begins again and the army goes to war. They will 581 00:51:23,480 --> 00:51:28,440 kill every living creature in their path that can't run from them. 582 00:51:41,160 --> 00:51:45,600 Normally they hunt other insects, but they will take small reptiles 583 00:51:45,600 --> 00:51:50,000 and even kill dogs and cows if they're tethered and can't escape. 584 00:51:50,000 --> 00:51:54,400 If the termite colony could be compared to an antelope, then this 585 00:51:54,400 --> 00:51:59,640 formidable super-organism must be the insect equivalent of a beast of prey, 586 00:51:59,640 --> 00:52:04,720 as powerful, ferocious and long-lived as many hunters of the jungle. 587 00:52:07,320 --> 00:52:12,000 Whatever limitations there may be in being small, these army ants 588 00:52:12,000 --> 00:52:15,760 and other social insects seem to have overcome them. 589 00:52:15,760 --> 00:52:20,240 Indeed, the more closely one watches insects, the more deeply impressed 590 00:52:20,240 --> 00:52:24,880 one is by their efficiency. No matter what man may wish to believe, 591 00:52:24,880 --> 00:52:28,720 insects are still masters of great parts of the world. 592 00:52:28,720 --> 00:52:32,560 They were, after all, the first animals to emerge onto dry land, 593 00:52:32,560 --> 00:52:35,440 then they lived by exploiting plants. 594 00:52:35,440 --> 00:52:39,760 Hundreds of thousands of species of them still do so today, 595 00:52:39,760 --> 00:52:43,600 chewing the leaves, gnawing the seeds and drinking the sap. 596 00:52:43,600 --> 00:52:47,440 And when other animals joined the insects on dry land, 597 00:52:47,440 --> 00:52:49,840 the insects exploited them too. 598 00:52:49,840 --> 00:52:52,720 They drank their blood, burrowed into their skins, 599 00:52:52,720 --> 00:52:56,560 they actually found a home within the tissues of living animals. 600 00:52:56,560 --> 00:53:00,880 Man has been doing battle with the insects ever since he first 601 00:53:00,880 --> 00:53:04,720 picked off the first flea and, I dare say, long before. 602 00:53:04,720 --> 00:53:09,520 Today we continue the fight, with fire, with radioactivity, 603 00:53:09,520 --> 00:53:14,320 with the most lethal poisons our chemists have been able to devise. 604 00:53:14,320 --> 00:53:19,360 And yet, so far, we have not managed to exterminate a single species.