1 00:01:10,767 --> 00:01:13,361 Rajasthan, central India. 2 00:01:13,527 --> 00:01:17,520 It's the middle of the morning, the day is beginning to warm up, 3 00:01:17,687 --> 00:01:20,884 and the animal community is in a relaxed mood. 4 00:01:21,047 --> 00:01:25,438 The sambar deer are cooling themselves in the shallows of the lake, 5 00:01:25,607 --> 00:01:31,398 looking for a bit of greenery to nibble and tolerantly taking the egrets for a ride. 6 00:01:33,567 --> 00:01:38,846 The egrets, too, are finding a little to eat - an insect, perhaps, picked out of the deer's coat. 7 00:01:39,007 --> 00:01:42,397 Nature isn't always red in tooth and claw. 8 00:01:42,567 --> 00:01:48,563 Different kinds of animals are often regular companions and get on well with one another. 9 00:02:11,967 --> 00:02:17,041 In the trees, langur monkeys are finishing their morning meal of leaves. 10 00:02:22,967 --> 00:02:27,358 They're fussy, untidy feeders, and drop a lot of the leaves, 11 00:02:27,527 --> 00:02:32,396 either by accident or because they don't fancy those particular ones. 12 00:02:34,087 --> 00:02:36,681 And that suits the spotted deer. 13 00:02:36,847 --> 00:02:42,444 In the dry season, the ground is parched and greenery worth eating very scarce. 14 00:02:42,607 --> 00:02:47,681 So even the smallest fragment of vegetation fallen from above is worth having. 15 00:02:47,847 --> 00:02:51,044 The deer follow the monkeys from tree to tree, 16 00:02:51,207 --> 00:02:55,678 picking up leaves that by themselves they couldn't reach. 17 00:03:16,727 --> 00:03:20,276 The monkeys also benefit from the presence of the deer. 18 00:03:20,447 --> 00:03:24,963 They sometimes come down to forage on the ground, and there they're vulnerable. 19 00:03:25,127 --> 00:03:31,521 The deer have a keener sense of smell, and may detect dangers that the monkeys can't see. 20 00:03:31,687 --> 00:03:34,884 And if they do, they will stamp a warning. 21 00:03:49,967 --> 00:03:56,361 We ourselves have very few such relationships, voluntarily, with other species of animals. 22 00:03:56,527 --> 00:04:01,521 Except, of course, with those animals that we have domesticated and enslaved. 23 00:04:01,687 --> 00:04:05,885 But back in our evolutionary past, we doubtless had many. 24 00:04:06,047 --> 00:04:11,440 Today, maybe we think we're so powerful or have become so detached from nature 25 00:04:11,607 --> 00:04:14,201 that we think we no longer need them. 26 00:04:14,367 --> 00:04:18,360 In the natural world, those relationships are widespread. 27 00:04:18,527 --> 00:04:24,523 Sometimes they've been in existence for so long that they have transformed the bodies of animals. 28 00:04:24,687 --> 00:04:27,759 Sometimes they are only just forming. 29 00:04:29,327 --> 00:04:33,206 This species of goby, for example, that lives around coral reefs, 30 00:04:33,367 --> 00:04:37,758 has, probably quite recently, struck up a relationship with a shrimp. 31 00:04:39,927 --> 00:04:43,476 The two regularly live together, sharing the same hole. 32 00:04:43,647 --> 00:04:48,277 But the goby plays no part in making it. It's dug entirely by the shrimp. 33 00:04:55,807 --> 00:05:01,996 The shrimp, in fact, seems to be a compulsive excavator, never content with its home as it is, 34 00:05:02,167 --> 00:05:06,445 always carrying out improvements and digging extensions. 35 00:05:07,807 --> 00:05:10,321 And the goby doesn't help. 36 00:05:11,887 --> 00:05:14,959 In fact, if anything, it gets in the way. 37 00:05:15,127 --> 00:05:21,123 But it's an essential companion for the shrimp, for this species of shrimp is virtually blind. 38 00:05:24,847 --> 00:05:30,240 The goby, on the other hand, has excellent eyesight, and is always on the alert. 39 00:05:32,327 --> 00:05:36,320 The shrimp, as it works, keeps in touch - literally - 40 00:05:36,487 --> 00:05:42,596 by continually flicking one of its long antennae over the fish to make sure it's still there. 41 00:05:42,767 --> 00:05:48,558 If the goby is out of the burrow, the shrimp knows that it's safe to carry on working. 42 00:05:53,127 --> 00:05:57,279 The goby is always on the lookout for something to eat 43 00:05:57,447 --> 00:06:01,440 and may have to make little excursions to get it. 44 00:06:04,527 --> 00:06:07,519 A tiny, edible morsel that floated by. 45 00:06:17,127 --> 00:06:22,121 But even while it's feeding, the shrimp's antenna is still in touch with it. 46 00:06:23,607 --> 00:06:28,601 Danger. And when the watchman retreats to safety, so does the shrimp. 47 00:06:34,287 --> 00:06:38,485 The goby, having fed, seems content to remain in the hole. 48 00:06:38,647 --> 00:06:41,445 Why expose yourself to danger unnecessarily? 49 00:06:41,607 --> 00:06:46,601 But the shrimp is perpetually keen to work and often appears to be hustling the goby, 50 00:06:46,767 --> 00:06:49,759 as though to persuade it to go out again. 51 00:06:52,847 --> 00:06:58,843 The shrimp collects its food from a little patch of alga that grows beside the burrow entrance. 52 00:07:08,447 --> 00:07:10,438 It knows just where that is, 53 00:07:10,607 --> 00:07:16,000 so it can nip across quickly and snatch a few clawfuls with the minimum of risk. 54 00:07:30,047 --> 00:07:34,518 All is well, as long as the shrimp keeps in touch with the goby. 55 00:07:34,687 --> 00:07:38,885 But if it ventures away, then there can be trouble. 56 00:07:39,047 --> 00:07:43,438 That was an anemone it blundered into, and it beats a swift retreat. 57 00:07:43,607 --> 00:07:46,075 For a moment, it seems lost. 58 00:07:50,927 --> 00:07:55,318 Then the goby comes over and contact is re-established. 59 00:07:55,487 --> 00:07:59,480 The partners are together again and all is well. 60 00:08:11,367 --> 00:08:15,360 So, two very different animals operate a partnership. 61 00:08:15,527 --> 00:08:21,284 The blind landlord provides the accommodation, and the tenant provides a guidance service. 62 00:08:24,847 --> 00:08:27,839 Hermit crabs live in a different kind of home. 63 00:08:28,007 --> 00:08:30,919 Instead of a hole, they use an empty shell. 64 00:08:31,087 --> 00:08:34,796 But they, too, can find themselves with lodgers. 65 00:08:45,127 --> 00:08:48,324 This one's companion is a ragworm. 66 00:09:06,447 --> 00:09:09,564 For the worm, this is a good place to be. 67 00:09:09,727 --> 00:09:15,359 It has a home where it's safe from predators, curled up inside the shell alongside the crab. 68 00:09:15,527 --> 00:09:21,045 And on its very doorstep, there's a regular supply of food brought there by the crab. 69 00:09:23,927 --> 00:09:28,717 Nonetheless, collecting a share of that food seems a fairly risky business. 70 00:09:28,887 --> 00:09:32,357 The crab's mandibles could easily chop the worm's head off. 71 00:09:32,527 --> 00:09:37,920 But the worm has had a lot of practice at this sort of thing. 72 00:09:39,327 --> 00:09:44,321 Whether the crab gets any benefit at all from the arrangement is rather doubtful, 73 00:09:44,487 --> 00:09:48,799 but there's not much it can do to get rid of its lodger anyway. 74 00:10:00,847 --> 00:10:03,236 A small octopus. 75 00:10:03,407 --> 00:10:06,399 Hermit crabs are one of its favourite foods. 76 00:10:34,287 --> 00:10:38,485 In the centre of those writhing arms it has a powerful beak 77 00:10:38,647 --> 00:10:42,117 with which it can drag the crab from its shell. 78 00:10:42,287 --> 00:10:46,883 And that's the end of both the hermit crab and its lodger. 79 00:10:55,567 --> 00:10:59,526 But this species of hermit crab recruits a bodyguard. 80 00:10:59,687 --> 00:11:05,876 Anemones have stings in their tentacles - stings that are strong enough to repel an octopus. 81 00:11:08,807 --> 00:11:11,526 Since the crab wanders about a great deal, 82 00:11:11,687 --> 00:11:15,680 its bodyguard, to be any good, has to travel with it. 83 00:11:23,727 --> 00:11:29,324 It's not easy to unstick an anemone from a rock, but the crab knows the trick. 84 00:11:29,487 --> 00:11:33,685 You have to tickle it around the edge of its bottom. 85 00:12:12,407 --> 00:12:17,197 You can tell that the anemone isn't particularly alarmed by this procedure 86 00:12:17,367 --> 00:12:22,361 because it hasn't closed up and is still confidently waving its tentacles. 87 00:12:43,807 --> 00:12:48,198 That makes three guardian anemones on the crab's shell. 88 00:12:48,367 --> 00:12:51,564 But is that enough to give it protection? 89 00:13:19,327 --> 00:13:21,795 The octopus is not sure. 90 00:13:42,207 --> 00:13:44,596 No, it's not worth it. 91 00:13:54,687 --> 00:13:57,155 So the crab has its bodyguards, 92 00:13:57,327 --> 00:13:59,761 and its bodyguards, for wages, 93 00:13:59,927 --> 00:14:05,524 are likely to get little bits and pieces that float by when the crab chews up its meals. 94 00:14:09,807 --> 00:14:15,803 It's not always easy to decide in these partnerships which is exploiting which. 95 00:14:15,967 --> 00:14:19,277 The balance of advantage is often very delicate. 96 00:14:19,447 --> 00:14:22,644 Take, for example, these ants in Australia. 97 00:14:22,807 --> 00:14:27,597 They are extremely ferocious and normally they'll rip apart any caterpillar. 98 00:14:27,767 --> 00:14:30,361 But see how they're treating this one. 99 00:14:33,527 --> 00:14:37,042 The caterpillar has on its back a number of little nipples 100 00:14:37,207 --> 00:14:40,199 which apparently fascinate the ants. 101 00:14:48,687 --> 00:14:52,475 0ne near its back end, when stimulated by an ant, 102 00:14:52,647 --> 00:14:57,038 produces a drop of liquid, honeydew, which the ant drinks. 103 00:15:06,207 --> 00:15:11,201 As the caterpillar grazes on leaves, the ants keep continuous guard over it, 104 00:15:11,367 --> 00:15:16,361 threatening anything that comes near it, so that even birds don't attack it. 105 00:15:32,607 --> 00:15:38,079 The caterpillar has to make sure that the ants don't forget what kind of caterpillar it is. 106 00:15:38,247 --> 00:15:42,525 If they think it's any other kind, they will tear it apart and eat it. 107 00:15:42,687 --> 00:15:47,681 So the caterpillar every now and then makes a characteristic buzzing vibration. 108 00:15:47,847 --> 00:15:52,841 Not only that, but on either side of the honeydew nipple there are two others. 109 00:15:53,007 --> 00:15:57,603 From these sprout little tentacles which apparently release a pheromone, 110 00:15:57,767 --> 00:16:02,158 a kind of perfume that keeps the ants happy and unaggressive. 111 00:16:03,327 --> 00:16:09,084 Tree ants build nests almost as big as footballs from the growing leaves of the tree. 112 00:16:10,687 --> 00:16:15,158 They feed on any small creature that happens to land in the tree. 113 00:16:17,607 --> 00:16:22,806 This grasshopper stood little chance. As soon as it landed, they set upon it. 114 00:16:22,967 --> 00:16:28,360 Now they are butchering it and carrying it back, piece by piece, to their nest. 115 00:16:32,167 --> 00:16:36,957 As well as this nest, the workers also construct small shelters. 116 00:16:37,127 --> 00:16:41,518 First, a team bridges two leaves and slowly pulls them together. 117 00:16:41,687 --> 00:16:45,680 0thers arrive carrying grubs, which they gently squeeze, 118 00:16:45,847 --> 00:16:49,840 so that the grubs are stimulated to produce a sticky silk. 119 00:16:50,007 --> 00:16:55,400 By passing the grubs back and forth, they weave a fabric that holds the two leaves together. 120 00:16:55,567 --> 00:16:59,276 They're making a shelter for their precious caterpillar. 121 00:17:00,407 --> 00:17:04,400 When it's complete, they guide the caterpillar into it. 122 00:17:11,527 --> 00:17:14,724 0nce in its shed, it'll be safe for the night. 123 00:17:14,887 --> 00:17:19,483 The ants look after it like farmers looking after a dairy cow. 124 00:17:19,647 --> 00:17:24,516 And their cow, in return, provides them with nourishing food. 125 00:17:34,887 --> 00:17:41,281 At this stage in their relationship, neither ant nor caterpillar seems to have the advantage. 126 00:17:41,447 --> 00:17:45,042 But this same species of ferocious stinging ant 127 00:17:45,207 --> 00:17:49,405 has also got a partnership with a different species of caterpillar, 128 00:17:49,567 --> 00:17:52,001 and there the result seems to be very different. 129 00:17:55,287 --> 00:17:58,677 This one has a glossy, horny shield on its back, 130 00:17:58,847 --> 00:18:03,921 and it, entirely of its own accord, marches right into the ants' nest. 131 00:18:06,207 --> 00:18:11,804 It is in no way deterred by the ants' threatening postures and sprays of formic acid. 132 00:18:11,967 --> 00:18:15,164 No matter what the ants do, they can't stop it. 133 00:18:15,327 --> 00:18:21,926 Deeper and deeper it goes, through the corridors of sewn leaves, right into the heart of the nest. 134 00:18:45,487 --> 00:18:50,083 It reaches the queen. If she is killed, the whole colony will die. 135 00:18:50,247 --> 00:18:54,206 But she is not what the intruder is looking for. 136 00:18:54,367 --> 00:19:00,363 The soldiers attack valiantly. Their jaws make little impression on the caterpillar's armour. 137 00:19:00,527 --> 00:19:05,237 Neither can they get underneath it and reach the soft, vulnerable body. 138 00:19:05,407 --> 00:19:09,480 0n it goes, until at last it reaches the nursery chambers 139 00:19:09,647 --> 00:19:12,115 where the developing grubs lie. 140 00:19:16,607 --> 00:19:20,122 Try as they might, they can't lift up the shield sufficiently 141 00:19:20,287 --> 00:19:23,085 to enable other defenders to get beneath. 142 00:19:32,087 --> 00:19:37,286 With the intruder actually within the nursery, the workers become totally confused. 143 00:19:37,447 --> 00:19:41,406 Some try to carry off the grubs to safety elsewhere. 144 00:19:51,087 --> 00:19:53,681 But they can't do it quickly enough. 145 00:19:54,647 --> 00:19:57,798 The caterpillar snatches a grub, pulls it under the shield, 146 00:19:57,967 --> 00:20:02,597 and then, secure beneath its armour, slowly eats it. 147 00:20:16,247 --> 00:20:21,480 As the season progresses, several of these armoured intruders make their way into the nest 148 00:20:21,647 --> 00:20:25,276 and there gorge themselves on ant grubs. 149 00:20:58,687 --> 00:21:05,320 After several weeks, the caterpillars have eaten all the grubs they need to grow to full size. 150 00:21:05,487 --> 00:21:11,483 Now, in the heart of the nest, they're ready to shed their armour and turn into butterflies. 151 00:21:11,647 --> 00:21:15,322 But how can a butterfly get through the ranks of the ant soldiers? 152 00:21:15,487 --> 00:21:20,402 Now, surely, they'll have a chance to get their revenge. 153 00:21:20,567 --> 00:21:24,765 Slowly, the insect hauls itself out of its horny armour. 154 00:21:41,407 --> 00:21:45,764 But it's a strange sort of butterfly that emerges. 155 00:21:50,367 --> 00:21:55,964 It's covered in scales that are so slippery that the ants can't get a proper grip on them. 156 00:22:03,687 --> 00:22:05,882 Those that do manage to bite 157 00:22:06,047 --> 00:22:11,644 get their jaws covered with a sort of fluff that they clearly find intensely irritating. 158 00:22:15,887 --> 00:22:20,085 So, at last, the murderous lodger goes free. 159 00:22:27,807 --> 00:22:33,200 Ants and caterpillars, like crabs and anemones, are about the same size. 160 00:22:33,367 --> 00:22:36,677 But if a lodger is very much smaller than its landlord, 161 00:22:36,847 --> 00:22:41,682 then it tends to live not so much with it as on it. 162 00:22:41,847 --> 00:22:44,566 Those monkeys over there, for example. 163 00:22:44,727 --> 00:22:47,525 They've got a number of tiny passengers. 164 00:23:00,847 --> 00:23:04,726 Like most mammals with hairy coats, they've got fleas. 165 00:23:04,887 --> 00:23:09,278 And when fleas bite and start sucking blood, they itch. 166 00:23:13,767 --> 00:23:20,081 It may be necessary to get a friend to help pick them out from parts that you can't reach. 167 00:23:24,647 --> 00:23:30,483 This, however, is not fur. This is the fabric of a bird's nest, and fleas live here, too. 168 00:23:33,967 --> 00:23:39,758 A young starling within two days of hatching is likely to have several dozen fleas. 169 00:23:42,247 --> 00:23:47,241 Fleas have six legs, just like any other insects, but they've lost their wings. 170 00:23:47,407 --> 00:23:52,640 Those would be an encumbrance to an animal crawling around among fur and feathers. 171 00:23:52,807 --> 00:23:57,597 Instead, they have powerful hind legs that enable them to jump onto their host. 172 00:23:57,767 --> 00:24:02,557 Their jaws have become specialised for sucking blood, and they feed on nothing else. 173 00:24:02,727 --> 00:24:07,323 They have to live on another animal, and they contribute nothing to its welfare. 174 00:24:07,487 --> 00:24:10,365 This is not a partnership. It's parasitism. 175 00:24:12,607 --> 00:24:16,395 Nor are fleas the only parasites in a bird's nest. 176 00:24:16,567 --> 00:24:19,161 Lice are there, eating feathers. 177 00:24:19,327 --> 00:24:24,321 They, too, are insects, and any one bird may have up to a dozen different kinds, 178 00:24:24,487 --> 00:24:30,278 each living on and eating a different kind of feather on the neck, the wings or the head. 179 00:24:34,527 --> 00:24:38,725 Insects seem to have a particular flair for parasitism. 180 00:24:38,887 --> 00:24:43,483 Every one of their main families has some members who've taken it up. 181 00:24:43,647 --> 00:24:47,640 But insects themselves can also be parasitised. 182 00:24:47,807 --> 00:24:53,518 This nest of bumble bees has been invaded by mites, diminutive cousins of spiders. 183 00:24:55,327 --> 00:25:00,321 They're so tiny that several hundred of them can sit on the leg of a bee. 184 00:25:02,007 --> 00:25:04,316 And they, too, itch. 185 00:25:11,767 --> 00:25:14,076 They get everywhere, 186 00:25:14,247 --> 00:25:19,560 and once they've found their way into a colony, they spread to every member of it. 187 00:25:31,967 --> 00:25:35,357 Mites are just as specialised as feather lice. 188 00:25:35,527 --> 00:25:40,396 These bee mites live nowhere else but on this particular species of bumble bee. 189 00:25:41,367 --> 00:25:47,522 And this flower, milkweed, is a staging post for one of the most specialised mites of all. 190 00:25:50,767 --> 00:25:53,361 Moths come to feed on the milkweed at night, 191 00:25:53,527 --> 00:25:59,523 dipping their long, threadlike tongues deep into the heart of the flowers to sip the nectar. 192 00:26:02,847 --> 00:26:06,442 But this moth is already infested with mites. 193 00:26:08,367 --> 00:26:11,643 Its ear, a tiny hole in the side of its head, 194 00:26:11,807 --> 00:26:15,595 has become the home of a whole colony of them. 195 00:26:20,767 --> 00:26:24,760 And a new colonist awaits on the flower itself. 196 00:26:30,527 --> 00:26:34,964 While the moth drinks, the mite crawls up its tongue. 197 00:27:14,567 --> 00:27:17,684 0nce on the moth's head, it knows, mysteriously, 198 00:27:17,847 --> 00:27:23,046 just which direction it must take through the jungle of fur to reach the ear. 199 00:27:23,207 --> 00:27:25,801 There is one great danger in all this. 200 00:27:25,967 --> 00:27:29,357 Blocking up an ear makes it useless to the moth. 201 00:27:29,527 --> 00:27:33,520 If the moth can't hear, it can't avoid the bats that hunt it. 202 00:27:33,687 --> 00:27:37,680 That would be as disastrous for the mites as for the moth. 203 00:27:37,847 --> 00:27:43,444 So the mites obligingly occupy only one ear and always leave the other free. 204 00:27:44,167 --> 00:27:49,764 Here they live and breed, using one part of the ear tube for stacking their droppings, 205 00:27:49,927 --> 00:27:54,717 another for laying their eggs, and yet another for rearing their grubs. 206 00:27:54,887 --> 00:27:59,677 And how do their offspring find another of these highly specialised homes? 207 00:27:59,847 --> 00:28:04,841 Why, of course, by clambering down their host's tongue as it drinks 208 00:28:05,007 --> 00:28:10,400 and waiting on the flower for another moth of the same species to turn up. 209 00:28:19,327 --> 00:28:22,205 But parasites are themselves preyed on. 210 00:28:22,367 --> 00:28:24,961 This mouse that lives in Central America 211 00:28:25,127 --> 00:28:30,121 regularly carries a dozen or so passengers wriggling around in its fur. 212 00:28:38,527 --> 00:28:43,920 They're beetles, and they were once thought to be parasites that sucked the mouse's blood, 213 00:28:44,087 --> 00:28:46,681 for they have large and powerful jaws. 214 00:28:46,847 --> 00:28:53,320 But, oddly, the mice that carry the most beetles are not the most anaemic, as you might expect. 215 00:28:53,487 --> 00:28:57,480 0n the contrary, they seem to be the most healthy. 216 00:28:57,647 --> 00:29:03,836 It turns out that the mouse's most serious parasites are here in the lining of the nest. 217 00:29:04,007 --> 00:29:07,204 Fleas and ticks that D0 suck its blood. 218 00:29:14,287 --> 00:29:20,476 Each mouse has several holes in the forest, and all are likely to be infested with these fleas. 219 00:29:22,007 --> 00:29:24,202 When a mouse settles down to rest in one, 220 00:29:24,367 --> 00:29:28,883 the beetles drop off and go hunting for the fleas in the nest lining. 221 00:29:29,047 --> 00:29:33,438 So the beetles, far from injuring the mouse, actually aid it. 222 00:29:43,207 --> 00:29:45,402 Got one. 223 00:29:51,607 --> 00:29:54,075 As far as a beetle is concerned, 224 00:29:54,247 --> 00:29:59,844 the mouse is a convenient transport system for getting from one hunting ground to another. 225 00:30:00,007 --> 00:30:05,525 The mouse that carries the most beetle passengers has the most flea-free life. 226 00:30:06,927 --> 00:30:10,203 These birds, too, are hunters of parasites. 227 00:30:10,367 --> 00:30:14,155 They're finches that live in the Galapagos Islands. 228 00:30:14,327 --> 00:30:18,115 And the creatures they help - the giant tortoises. 229 00:30:25,447 --> 00:30:29,759 You can hardly scratch yourself if you have legs like these. 230 00:30:31,887 --> 00:30:34,799 Yet tortoises, like so many other animals, 231 00:30:34,967 --> 00:30:39,199 are pestered by skin parasites, especially ticks. 232 00:30:40,007 --> 00:30:45,604 The finches eat mainly seeds, but ticks apparently make a welcome change. 233 00:30:51,087 --> 00:30:56,081 When there's a tortoise nearby and the finches want a meal with a difference, 234 00:30:56,247 --> 00:31:01,082 they signal to the tortoise by jumping up and down in front of it. 235 00:31:02,287 --> 00:31:06,883 The tortoise reacts to the finches' advances in a remarkable way. 236 00:31:07,047 --> 00:31:13,805 It stiffens its legs, so that its body is lifted clear of the ground, and cranes up its neck. 237 00:31:17,087 --> 00:31:20,875 The invitation is an unmistakeable one. 238 00:31:26,287 --> 00:31:29,404 There's no way that the tortoise could pick off parasites 239 00:31:29,567 --> 00:31:34,436 from the places that these attendants manage to reach. 240 00:31:51,447 --> 00:31:54,041 A few minutes' servicing by the finches 241 00:31:54,207 --> 00:31:58,200 is quite enough to clear the tortoise of most of its pests. 242 00:31:58,367 --> 00:32:00,835 Another satisfied customer. 243 00:32:04,127 --> 00:32:08,598 Fish have the same sort of problem, and the same sort of solution. 244 00:32:08,767 --> 00:32:15,286 The huge manta ray is troubled by sea lice and barnacles that burrow into its skin. 245 00:32:18,967 --> 00:32:24,360 But it has other company, an attendant fleet of small fish that travel with it. 246 00:32:24,527 --> 00:32:31,126 When the opportunity arises, they swim over their host's body, even inside its gaping mouth, 247 00:32:31,287 --> 00:32:33,801 picking off the passengers. 248 00:32:51,447 --> 00:32:57,636 Like giant tortoises, fish with skin problems patronise regular cleaning establishments. 249 00:33:00,767 --> 00:33:05,158 This grouper hangs in the water at this special place on the reef, 250 00:33:05,327 --> 00:33:10,640 and small wrasse that have been waiting amongst the coral start fussing around it, 251 00:33:10,807 --> 00:33:14,356 even daring to swim inside the huge jaws. 252 00:33:23,447 --> 00:33:26,439 It's not only fish that work as cleaners. 253 00:33:26,607 --> 00:33:30,202 This moray eel is being tended by a shrimp. 254 00:33:32,887 --> 00:33:35,276 0pen wide, please. 255 00:33:51,647 --> 00:33:54,844 Amazingly, the cleaners are never harmed... 256 00:33:56,767 --> 00:33:59,156 ..even though they tickle. 257 00:34:08,207 --> 00:34:13,201 These shrimps are really quite large, big enough to make a reasonable meal, 258 00:34:13,367 --> 00:34:16,040 but they're never injured, either. 259 00:34:23,807 --> 00:34:28,597 Regular customers come back to these cleaning stations every few days. 260 00:34:28,767 --> 00:34:33,557 Although the staff of wrasse and shrimps can deal with as many as 50 an hour, 261 00:34:33,727 --> 00:34:38,118 there are often queues of itchy fish waiting their turn. 262 00:34:43,567 --> 00:34:47,765 Some fish, however, have their own personal valets. 263 00:34:50,887 --> 00:34:57,360 Suckerfish, or remoras, have a fin on their back that has been modified into a sucker so powerful 264 00:34:57,527 --> 00:35:02,237 that it's almost impossible to pull off a remora if it wants to stay on. 265 00:35:02,407 --> 00:35:05,001 They travel with their host wherever it goes 266 00:35:05,167 --> 00:35:10,958 and slip around its body, picking off parasites, whenever there's an opportunity to do so. 267 00:35:28,447 --> 00:35:32,440 Giraffe, like many other big game animals in Africa, 268 00:35:32,607 --> 00:35:35,440 also have their own personal staff. 269 00:35:42,487 --> 00:35:48,483 0xpeckers live almost permanently on their hosts' bodies, scuttling about all over it. 270 00:35:57,167 --> 00:36:01,877 0n this spacious, patterned stage, they act out almost all their lives. 271 00:36:02,047 --> 00:36:07,405 Here they argue and court. Here, too, they feed their newly fledged young. 272 00:36:07,567 --> 00:36:11,560 They can't, it's true, nest here - they do that in holes in trees - 273 00:36:11,727 --> 00:36:15,720 but they do line those holes with hair from their host's body, 274 00:36:15,887 --> 00:36:18,879 so that, presumably, they'll still feel at home. 275 00:36:23,607 --> 00:36:29,921 Their claws are so long that they can cling in almost any position and move in any direction. 276 00:36:30,087 --> 00:36:35,480 Their beak is flattened, so that it slips easily between the long hairs of the giraffe's coat 277 00:36:35,647 --> 00:36:38,878 as they scissor through it searching for ticks. 278 00:36:42,047 --> 00:36:44,436 And they get everywhere, 279 00:36:44,607 --> 00:36:46,996 on young and on old. 280 00:36:52,887 --> 00:36:56,880 Even when the animal moves off, they will hang on 281 00:36:57,047 --> 00:37:01,245 with the skill and unconcern of accomplished jockeys. 282 00:37:08,607 --> 00:37:14,603 But oxpeckers are a mixed blessing. The ticks they eat are full of the giraffe's blood. 283 00:37:14,767 --> 00:37:19,363 But sometimes they take that blood directly from an open wound. 284 00:37:19,527 --> 00:37:24,521 And by doing that, they're not improving their host's health, but damaging it, 285 00:37:24,687 --> 00:37:29,477 keeping the wound open long after it would otherwise have healed. 286 00:37:30,767 --> 00:37:33,156 Even so, without them, 287 00:37:33,327 --> 00:37:38,321 giraffes would be more seriously troubled by their skin parasites than they are. 288 00:37:44,327 --> 00:37:49,720 We ourselves, of course, can also get infested with ticks and fleas if we're not careful. 289 00:37:49,887 --> 00:37:53,675 They're everywhere, particularly in the rainforest. 290 00:38:00,127 --> 00:38:05,520 0ne has a reasonable chance of getting rid of animals that settle on your outside. 291 00:38:05,687 --> 00:38:08,679 I can flick off these ticks. 292 00:38:09,767 --> 00:38:15,842 If you can't do it for yourself, maybe you can get an oxpecker or a cleaner fish to do it for you. 293 00:38:16,007 --> 00:38:21,718 But if the parasite settles not on the outside of your body, but manages to get inside it, 294 00:38:21,887 --> 00:38:23,878 that's a very different matter. 295 00:38:28,087 --> 00:38:32,080 The corridors and chambers of an animal's digestive system 296 00:38:32,247 --> 00:38:36,240 offer great advantages to any creature that can dwell in them. 297 00:38:36,407 --> 00:38:39,001 Inside here they are secure from enemies 298 00:38:39,167 --> 00:38:42,045 and washed continuously by a nutritious soup 299 00:38:42,207 --> 00:38:47,804 that their host has already chewed, mashed and partially digested for itself. 300 00:38:47,967 --> 00:38:53,758 All they have to do is to absorb it through their skin. They don't even need a mouth. 301 00:38:55,887 --> 00:38:59,675 The animals that are best suited to this interior life 302 00:38:59,847 --> 00:39:05,365 are those long, spineless, legless creatures we call collectively worms. 303 00:39:05,527 --> 00:39:09,520 Flat, ribbon-shaped tapeworms hang onto the walls of the gut 304 00:39:09,687 --> 00:39:12,884 with a crown of hooks that encircle their head. 305 00:39:18,327 --> 00:39:23,117 In the long corridors of the intestines, roundworms proliferate. 306 00:39:23,287 --> 00:39:26,324 Every backboned animal that has been thoroughly examined, 307 00:39:26,487 --> 00:39:30,196 whether fish or amphibian, reptile, bird or mammal, 308 00:39:30,367 --> 00:39:34,121 has proved to be the host of a roundworm. 309 00:39:34,287 --> 00:39:38,883 These living in a gut merely rob the host of some of its food. 310 00:39:39,047 --> 00:39:44,246 But they may spread to cause severe damage to the liver and the lungs. 311 00:39:44,407 --> 00:39:48,195 0ther roundworms, too, cause serious problems. 312 00:39:49,607 --> 00:39:55,921 There are some as thin as threads of cotton that collect in the valves of the heart, 313 00:39:56,087 --> 00:39:59,682 blocking them so seriously that their host dies. 314 00:40:03,647 --> 00:40:08,038 The young of such threadworms, swimming around in the bloodstream, 315 00:40:08,207 --> 00:40:12,200 depend on biting insects to transfer them to another host. 316 00:40:12,367 --> 00:40:15,439 During the day, they swim in blood vessels. 317 00:40:15,607 --> 00:40:21,204 At night, when mosquitoes are biting, they move up into the capillaries just beneath the skin, 318 00:40:21,367 --> 00:40:26,361 so that when a mosquito does start to suck their host's blood, they are taken up. 319 00:40:26,527 --> 00:40:29,325 They continue to grow inside the mosquito. 320 00:40:29,487 --> 00:40:36,279 When, in due course, it bites some other animal, they're transferred into a new host, a new home. 321 00:40:37,287 --> 00:40:41,485 0thers, smaller still, that wriggle among the blood corpuscles, 322 00:40:41,647 --> 00:40:45,845 belong to the most ancient of all animal groups, the protozoans. 323 00:40:46,007 --> 00:40:48,805 They first got inside animals so long ago 324 00:40:48,967 --> 00:40:52,243 that most of their hosts have developed an immunity to them. 325 00:40:52,407 --> 00:40:56,559 But human beings, those most recent of mammals, have not yet done so. 326 00:40:56,727 --> 00:41:01,084 In them, they cause sleeping sickness and death. 327 00:41:01,247 --> 00:41:07,038 The problem that faces all internal parasites is how to get their offspring into another host. 328 00:41:07,207 --> 00:41:11,997 Tiny ones, like the protozoans, may be transferred by biting insects. 329 00:41:12,167 --> 00:41:16,524 Bigger ones, like this roundworm, have to use other methods. 330 00:41:16,687 --> 00:41:22,080 The first stage, getting their eggs to the outside world, is easy. 331 00:41:27,447 --> 00:41:32,840 This roundworm, full of eggs, simply sheds them into its host's gut 332 00:41:33,007 --> 00:41:35,726 so that they fall out with its droppings. 333 00:41:37,207 --> 00:41:42,076 0nce in the soil, they may lie dormant for some considerable time. 334 00:41:42,247 --> 00:41:48,243 But eventually, when conditions are suitable, the temperature just right and moisture around, 335 00:41:48,407 --> 00:41:50,716 they begin to hatch. 336 00:42:09,047 --> 00:42:12,039 The tiny worms crawl up leaves of grass, 337 00:42:12,207 --> 00:42:16,598 and there await the moment when a hungry mouth will crop the grass 338 00:42:16,767 --> 00:42:19,759 and they will get carried into another stomach. 339 00:42:19,927 --> 00:42:22,919 Such transfers are not always straightforward. 340 00:42:23,087 --> 00:42:28,639 Sometimes the complexities of the route they follow are almost beyond imagining. 341 00:42:30,007 --> 00:42:32,601 Denmark. A morning in summer. 342 00:42:35,367 --> 00:42:40,361 There has been a shower of rain, and the meadows and woodlands are drenched. 343 00:42:49,447 --> 00:42:54,475 Snails are slowly crawling around through the wet leaves, grazing. 344 00:42:54,647 --> 00:43:00,040 They're feeding on algae and rotting vegetable matter of one kind and another. 345 00:43:00,207 --> 00:43:03,005 Early morning is the best time for them. 346 00:43:03,167 --> 00:43:06,079 The sun is not yet hot enough to dry them out 347 00:43:06,247 --> 00:43:11,446 and they can explore parts of the vegetation they can't reach at other times. 348 00:43:29,287 --> 00:43:32,802 But this one is different from the others. 349 00:43:35,567 --> 00:43:39,526 Its left tentacle is swollen and pulsating. 350 00:43:39,687 --> 00:43:42,076 It has a parasite. 351 00:43:44,807 --> 00:43:50,200 A few months ago, the snail took in, along with its normal food, some bird droppings. 352 00:43:50,367 --> 00:43:55,361 Within them were the tiny eggs of a fluke that was living within the bird's gut. 353 00:43:55,527 --> 00:44:01,318 Those hatched and the parasite developed, taking over much of the snail's body. 354 00:44:01,487 --> 00:44:03,478 As the sun shines brighter, 355 00:44:03,647 --> 00:44:09,836 the parasite extends a striped, muscular bag packed with larvae into the snail's tentacle. 356 00:44:10,007 --> 00:44:14,000 If it has the choice, it nearly always picks the left one. 357 00:44:14,167 --> 00:44:20,356 Birds rarely eat whole snails. They're far too big, and few can extract them from their shells. 358 00:44:20,527 --> 00:44:26,318 Nonetheless, the larvae must reach the body of another bird to develop further. 359 00:44:26,487 --> 00:44:31,720 For some reason, the presence of the parasite changes the snail's behaviour. 360 00:44:31,887 --> 00:44:35,880 As the day wears on, it does not, like uninfected snails, 361 00:44:36,047 --> 00:44:40,325 crawl back into the cool undergrowth out of harm's way. 362 00:44:40,487 --> 00:44:43,285 Instead, it remains exposed, out in the open. 363 00:44:43,447 --> 00:44:45,756 Dangerously so. 364 00:44:50,647 --> 00:44:53,639 Now there is a parasite in each tentacle. 365 00:45:04,287 --> 00:45:09,759 Perhaps they look like caterpillars or tasty worms. Maybe they just look odd. 366 00:45:09,927 --> 00:45:13,715 But certainly the flycatcher finds them interesting. 367 00:45:32,007 --> 00:45:36,205 The connection has been made, the circle is complete. 368 00:45:36,367 --> 00:45:38,961 Another bird has become infected. 369 00:45:41,247 --> 00:45:46,446 Inside the bird, the striped bag releases its multitudes of larvae. 370 00:45:46,607 --> 00:45:51,078 They soon move through the bird's body and take up residence in its gut, 371 00:45:51,247 --> 00:45:54,239 and the whole cycle starts all over again. 372 00:45:58,687 --> 00:46:04,284 Flukes are related to the flatworms that live independent lives in ponds and swamps. 373 00:46:04,447 --> 00:46:09,043 But they've found their greatest success as internal parasites. 374 00:46:09,207 --> 00:46:15,521 Some reside in the liver. 0ther kinds anchor themselves in the bladder, the lungs or the gut. 375 00:46:15,687 --> 00:46:18,997 Most are capable of causing serious disease. 376 00:46:20,047 --> 00:46:24,723 All internal parasites, however, do not necessarily injure their hosts. 377 00:46:24,887 --> 00:46:27,685 Some, indeed, actually help them. 378 00:46:27,847 --> 00:46:32,637 These microscopic organisms, undoubtedly alive and arguably animals 379 00:46:32,807 --> 00:46:37,801 since they don't have chlorophyll, like plants, with which to manufacture their food, 380 00:46:37,967 --> 00:46:40,765 live in the stomachs of most large animals. 381 00:46:40,927 --> 00:46:46,320 They are able, chemically, to break down the cellulose which forms most plant tissues, 382 00:46:46,487 --> 00:46:51,686 something the digestive juices of most large, plant-eating animals can't do. 383 00:46:53,007 --> 00:46:58,001 Their free-living ancestors swam in ponds, as some of their relatives still do today. 384 00:46:58,167 --> 00:47:03,161 These are members of the family that have simply found a warmer, darker pond, 385 00:47:03,327 --> 00:47:08,321 and one that is extraordinarily rich in edible material - a stomach. 386 00:47:13,647 --> 00:47:16,639 So a buffalo, like most wild animals, 387 00:47:16,807 --> 00:47:20,402 is not, as it might appear, a single individual. 388 00:47:21,327 --> 00:47:23,636 It's a walking zoo. 389 00:47:23,807 --> 00:47:26,799 Its oxpecker companions are obvious enough, 390 00:47:26,967 --> 00:47:31,358 but if we looked closer we would find ticks boring into its skin, 391 00:47:31,527 --> 00:47:35,918 in its mouth, leeches that it picked up when it drank from the river. 392 00:47:36,087 --> 00:47:41,480 Tapeworms are trailing through its guts, flukes are moored in the veins of its liver, 393 00:47:41,647 --> 00:47:46,675 and protozoans are swimming in its blood and swilling around in its stomach. 394 00:47:46,847 --> 00:47:52,240 It's a whole community of different animals that have been committed by evolution, 395 00:47:52,407 --> 00:47:56,480 for better or for worse, in sickness and in health, 396 00:47:56,647 --> 00:47:58,956 to live together.