1 00:00:05,000 --> 00:00:10,720 Swarms are one of the greatest spectacles on earth. 2 00:00:10,720 --> 00:00:15,320 At times horrifying, and also a thing of wonder. 3 00:00:18,300 --> 00:00:19,840 As part of the swarm, 4 00:00:19,840 --> 00:00:23,720 the smallest of creatures can become a force of nature. 5 00:00:23,720 --> 00:00:26,720 I'm George McGavin, a zoologist and explorer 6 00:00:26,720 --> 00:00:30,800 and I'll be travelling the globe to get right into the heart 7 00:00:30,800 --> 00:00:34,000 of some of the world's most impressive swarms. 8 00:00:34,000 --> 00:00:35,600 HE LAUGHS 9 00:00:38,800 --> 00:00:43,400 I want to show you that far from being the ultimate nightmare, 10 00:00:43,400 --> 00:00:47,840 swarms are one of nature's most ingenious solutions. 11 00:00:47,840 --> 00:00:48,840 Ow! 12 00:00:59,680 --> 00:01:01,840 Swarms are extremely powerful. 13 00:01:07,560 --> 00:01:08,800 By joining together, 14 00:01:08,800 --> 00:01:12,640 even the simplest of creatures can achieve the impossible. 15 00:01:14,680 --> 00:01:19,760 And by understanding how swarms work, 16 00:01:19,760 --> 00:01:23,160 we're gaining some fascinating insight into our own lives. 17 00:01:32,920 --> 00:01:37,200 My journey begins in North America, in southern California. 18 00:01:45,960 --> 00:01:49,760 I am hitting the highway in pursuit of a swarm most sane people 19 00:01:49,760 --> 00:01:51,880 would go out of their way to avoid. 20 00:01:54,480 --> 00:01:55,920 At some point, 21 00:01:55,920 --> 00:02:00,240 this little insect's sting might have totally ruined your day. 22 00:02:00,240 --> 00:02:03,240 Whoo, damn! 23 00:02:03,240 --> 00:02:06,880 But in extreme cases, this is a swarm that can kill. 24 00:02:06,880 --> 00:02:10,920 I don't think you want to be outside right now. There is a swarm of bees. 25 00:02:12,760 --> 00:02:13,880 The honeybee. 26 00:02:19,800 --> 00:02:21,520 A terrifying swarm, 27 00:02:21,520 --> 00:02:27,160 but one that worldwide is worth a staggering $180 billion a year. 28 00:02:29,640 --> 00:02:33,280 Without them, over a third of all the food we eat wouldn't exist. 29 00:02:36,000 --> 00:02:41,640 And nowhere is the bee's pollinating handiwork more crucial than here. 30 00:02:41,640 --> 00:02:42,860 California. 31 00:02:46,720 --> 00:02:50,240 More fruit and vegetables are produced in this state 32 00:02:50,240 --> 00:02:53,000 than anywhere else in America. 33 00:02:53,000 --> 00:02:57,040 And bees are so important to the process that every year, 34 00:02:57,040 --> 00:03:01,280 farmers actually import almost 2 million hive-loads of them. 35 00:03:04,920 --> 00:03:09,480 This is the perfect place to understand the secret of the swarm 36 00:03:09,480 --> 00:03:13,480 that takes group intelligence to a completely new level. 37 00:03:19,560 --> 00:03:21,200 To understand how it works, 38 00:03:21,200 --> 00:03:25,920 I need to get right to the start of the swarm, to the moment a queen 39 00:03:25,920 --> 00:03:30,960 gathers a loyal team of workers around her and goes house hunting. 40 00:03:30,960 --> 00:03:33,760 Now, in this temporary swarming state, 41 00:03:33,760 --> 00:03:35,240 they are really non-aggressive 42 00:03:35,240 --> 00:03:37,240 because they're not protecting anything, 43 00:03:37,240 --> 00:03:39,080 they're not protecting young, or honey - 44 00:03:39,080 --> 00:03:41,360 they are simply protecting or shielding the queen 45 00:03:41,360 --> 00:03:45,320 that's in the heart of their swarm until a new home is found, 46 00:03:45,320 --> 00:03:48,240 and they are so relaxed non-aggressive 47 00:03:48,240 --> 00:03:52,120 that I can actually put my hand right into the swarm here 48 00:03:52,120 --> 00:03:56,520 and just jiggle off a little handful of bees. 49 00:03:57,800 --> 00:04:00,840 Now, there's no way I could do this with a normal hive. 50 00:04:00,840 --> 00:04:04,880 It's only possible when they're in this temporary swarming state. 51 00:04:04,880 --> 00:04:08,400 Now, if I can persuade the worker bees that I'm a queen bee, 52 00:04:08,400 --> 00:04:10,240 they should swarm around me. 53 00:04:13,000 --> 00:04:16,880 It's only going to be possible because the swarm sticks together 54 00:04:16,880 --> 00:04:20,920 by following chemical signals called pheromones. 55 00:04:20,920 --> 00:04:23,800 Looks have nothing to do with it. 56 00:04:23,800 --> 00:04:28,560 It's an attraction so powerful that the bees should be prepared 57 00:04:28,560 --> 00:04:32,080 to ignore the obvious and accept me as their queen. 58 00:04:32,080 --> 00:04:33,720 To put it to the test, 59 00:04:33,720 --> 00:04:38,800 honey bee expert Norman Gary is giving me a queen bee makeover. 60 00:04:38,800 --> 00:04:45,000 I'm going to put droplets of a pheromone mix on your clothing. 61 00:04:45,000 --> 00:04:48,600 That pheromone is the odour that the queen bee emits 62 00:04:48,600 --> 00:04:51,640 that makes the other workers swarm around it. 63 00:04:51,640 --> 00:04:56,240 These are all females, did you know that? The females are now loving you. 64 00:04:56,240 --> 00:04:57,720 Yeah. 65 00:04:57,720 --> 00:05:00,640 Have fun, George! Hah! 66 00:05:01,760 --> 00:05:04,200 'There's no backing out now. 67 00:05:04,200 --> 00:05:08,280 'My only defence is a bit of insect repellent on my face.' 68 00:05:08,280 --> 00:05:10,640 I'm gonna start low, George, 69 00:05:10,640 --> 00:05:13,240 because they tend to migrate up, so here we go. 70 00:05:14,840 --> 00:05:16,960 There you go. 71 00:05:20,440 --> 00:05:23,520 'At this stage, it's hard to tell 72 00:05:23,520 --> 00:05:25,960 'whether the bees are going to stick around. 73 00:05:25,960 --> 00:05:30,120 'And if I'm honest, right now, I'm not sure I want them to.' 74 00:05:30,120 --> 00:05:33,200 This is not funny, because... 75 00:05:37,000 --> 00:05:40,080 It's in my eye, it's in my eye! Argh! 76 00:05:42,400 --> 00:05:44,920 Just relax. 77 00:05:44,920 --> 00:05:48,280 I am relaxed. I'm so chilled, I can't tell you. 78 00:05:51,560 --> 00:05:54,000 It looks like the workers have been fooled. 79 00:05:54,000 --> 00:05:58,000 I'm really beginning to get a sense of what it must feel like to 80 00:05:58,000 --> 00:06:04,080 be the queen bee in the centre of a massive swarm of bees. 81 00:06:04,080 --> 00:06:07,600 And being part of the swarm is starting to feel even weirder 82 00:06:07,600 --> 00:06:12,240 than it looks. I can now feel the weight of the bees on my chest. 83 00:06:12,240 --> 00:06:15,760 There's a fair few of them and collectively, 84 00:06:15,760 --> 00:06:20,320 they're beginning to feel quite heavy, like wearing a wet shirt. 85 00:06:20,320 --> 00:06:23,040 The other thing that's quite obvious is the heat. 86 00:06:23,040 --> 00:06:25,880 Because I'm covered in a layer of active bees 87 00:06:25,880 --> 00:06:28,960 that are vibrating their wings, they are generating 88 00:06:28,960 --> 00:06:32,760 quite a bit of heat and that's being transmitted to me through my shirt. 89 00:06:32,760 --> 00:06:35,960 I can really feel like I'm wearing a sort of woollen jumper. 90 00:06:38,840 --> 00:06:41,520 'It's incredibly unsettling. 91 00:06:41,520 --> 00:06:45,560 'I'm only safe from attack because this swarm is in 92 00:06:45,560 --> 00:06:49,680 'this temporary state, but that needs to change. 93 00:06:49,680 --> 00:06:53,680 'The bees face a critical decision on where to set up 94 00:06:53,680 --> 00:06:55,880 'their permanent home. 95 00:06:55,880 --> 00:06:59,200 'It's vital they get it right. 96 00:06:59,200 --> 00:07:02,400 'Get it wrong, and the swarm will die. 97 00:07:02,400 --> 00:07:08,280 'So how do 40,000 individuals reach a unanimous decision?' 98 00:07:08,280 --> 00:07:11,360 Although the queen is central to the formation of the swarm, 99 00:07:11,360 --> 00:07:14,280 it's not her that takes any part in the decision 100 00:07:14,280 --> 00:07:17,680 about where the swarm will end up, where they'll have their new home. 101 00:07:17,680 --> 00:07:20,400 But in order to show you how that works, 102 00:07:20,400 --> 00:07:23,320 I'm going to have to move this swarm off me. 103 00:07:28,000 --> 00:07:31,160 Wonderful. Perfect, perfect. 104 00:07:33,080 --> 00:07:35,440 With the swarm now airborne, 105 00:07:35,440 --> 00:07:38,520 they don't have long to make a decision 106 00:07:38,520 --> 00:07:42,640 and to see how they do it, we've set up an experiment. 107 00:07:42,640 --> 00:07:46,440 I've given the bees a choice of three new hives, 108 00:07:46,440 --> 00:07:48,880 only one of which is suitable. 109 00:07:48,880 --> 00:07:53,840 Hive A has a small enough entrance to keep out any predators, 110 00:07:53,840 --> 00:07:57,320 but it's not big enough for the swarm to grow. 111 00:07:57,320 --> 00:08:01,560 Hive B is larger, so there's room for the bees to expand, 112 00:08:01,560 --> 00:08:04,760 but the entrance is too big to protect them. 113 00:08:04,760 --> 00:08:08,200 It all rests on hive C. 114 00:08:08,200 --> 00:08:11,400 The one they should really go for is this one over here. 115 00:08:11,400 --> 00:08:14,320 It's the right size, it's got room for growth, 116 00:08:14,320 --> 00:08:16,640 the entrance hole is also the right size, 117 00:08:16,640 --> 00:08:22,480 so this, if I was a bee, this is the one I'd be going for. 118 00:08:22,480 --> 00:08:26,960 The question is, will the bees choose the right one? 119 00:08:26,960 --> 00:08:32,280 The first thing the swarm does is send out the scouts. 120 00:08:32,280 --> 00:08:36,680 It's their job to search for a new home, inspect the premises, 121 00:08:36,680 --> 00:08:40,120 and report back. 122 00:08:40,120 --> 00:08:44,800 They're looking for a nice, roomy hive, safe from predators 123 00:08:44,800 --> 00:08:50,680 and south-facing, to make the most of the early morning sun. 124 00:08:50,680 --> 00:08:54,360 And after a thorough investigation of all three hives, 125 00:08:54,360 --> 00:08:57,360 it's time to head back to base. 126 00:08:59,840 --> 00:09:03,680 What's really amazing about all this is the way that the scout bees 127 00:09:03,680 --> 00:09:07,120 communicate that vital information back to the swarm. 128 00:09:13,360 --> 00:09:15,440 It's all about the waggle dance. 129 00:09:22,360 --> 00:09:24,400 With their best dance moves, 130 00:09:24,400 --> 00:09:28,080 the scouts tell other bees which direction to go. 131 00:09:28,080 --> 00:09:30,920 The length of the waggling gives them a distance. 132 00:09:30,920 --> 00:09:36,680 One second of waggle equals half a mile of flying. But that's not all. 133 00:09:36,680 --> 00:09:40,040 The energy that they perform that dance 134 00:09:40,040 --> 00:09:43,520 indicates the quality of the house. Look at this one here. 135 00:09:43,520 --> 00:09:47,800 She is really going for it. This is a really high-energy waggle dance. 136 00:09:47,800 --> 00:09:50,840 Lots of enthusiasm. She's doing it over and over again. 137 00:09:50,840 --> 00:09:53,720 And that will tell the rest of the swarm 138 00:09:53,720 --> 00:09:58,320 that what she's found could be the perfect home. 139 00:09:58,320 --> 00:10:00,760 We used to think that the decision 140 00:10:00,760 --> 00:10:03,400 was all down to the bees' waggle dance. 141 00:10:03,400 --> 00:10:09,320 When enough bees dance for the same hive, a decision was made. 142 00:10:09,320 --> 00:10:13,160 But recently, scientists realised there was something much 143 00:10:13,160 --> 00:10:15,840 more interesting happening on the dance floor. 144 00:10:19,640 --> 00:10:23,680 Some of the dancing bees were on the receiving end 145 00:10:23,680 --> 00:10:27,680 of a sneaky head-butt, a signal to stop dancing. 146 00:10:27,680 --> 00:10:32,080 So it's actually a combination of enthusiasm and bullying 147 00:10:32,080 --> 00:10:37,360 that helps the bees agree and prevents a decision deadlock. 148 00:10:37,360 --> 00:10:40,440 So what does this swarm make of the three hives? 149 00:10:42,800 --> 00:10:45,080 Jeez! They're everywhere. 150 00:10:45,080 --> 00:10:49,320 Well, those 40,000 bees have now taken to the air, 151 00:10:49,320 --> 00:10:52,920 absolutely full of...the noise is incredible 152 00:10:52,920 --> 00:10:56,200 and they're all heading to that hive over there 153 00:10:56,200 --> 00:10:58,000 and so far, not one sting. 154 00:10:58,000 --> 00:11:00,080 Ooh! Ow! 155 00:11:00,080 --> 00:11:05,080 Something just got me! Sorry, correction - one sting! 156 00:11:05,080 --> 00:11:07,800 And while two of the hives are still empty, 157 00:11:07,800 --> 00:11:13,480 hive C is proving popular and the bees are moving in en masse. 158 00:11:13,480 --> 00:11:16,320 They've made the decision collectively 159 00:11:16,320 --> 00:11:20,000 and they've picked this hive. This was the one I thought they'd pick. 160 00:11:20,000 --> 00:11:22,240 It's absolutely right, is the right size. 161 00:11:22,240 --> 00:11:24,880 It's the perfect angle, the perfect everything. 162 00:11:27,240 --> 00:11:29,960 And it's their group intelligence, 163 00:11:29,960 --> 00:11:33,200 the ability to use the power of the swarm to make the right 164 00:11:33,200 --> 00:11:37,240 decision that makes honeybees the ultimate team... 165 00:11:40,880 --> 00:11:44,400 Because it's a fact that hundreds of individuals 166 00:11:44,400 --> 00:11:48,240 make a better decision together than a single expert. 167 00:11:50,040 --> 00:11:54,920 And that's something both animal swarms and humans have in common. 168 00:12:00,000 --> 00:12:04,840 It's a bizarre phenomenon first noticed back in 1906 169 00:12:04,840 --> 00:12:07,720 at a county show much like this one. 170 00:12:09,000 --> 00:12:10,200 Ha ha! 171 00:12:16,040 --> 00:12:21,160 Scientists were amazed by what happens during a simple competition 172 00:12:21,160 --> 00:12:24,320 asking people to guess the weight of a cow. 173 00:12:24,320 --> 00:12:27,240 When they analysed the results, not only was the average 174 00:12:27,240 --> 00:12:31,040 of everyone's guesses more accurate than the winning guess, 175 00:12:31,040 --> 00:12:35,320 it was also a much better guess than that of the experts who took part. 176 00:12:35,320 --> 00:12:38,400 So today, we're going to put it to the test 177 00:12:38,400 --> 00:12:39,600 with the help of Zinny here. 178 00:12:43,280 --> 00:12:46,920 We asked a selection of people at the Royal Bath Show 179 00:12:46,920 --> 00:12:48,680 to guess Zinny's weight. 180 00:12:48,680 --> 00:12:53,920 How accurate will they be as a group and can they beat one of the pros? 181 00:12:53,920 --> 00:12:56,080 Right, well, the results are in 182 00:12:56,080 --> 00:13:00,320 and all I've got to do now is to add up all the estimates 183 00:13:00,320 --> 00:13:04,640 from the crowd, get a total, 184 00:13:04,640 --> 00:13:08,400 divide that by the number of people who guessed... 185 00:13:09,360 --> 00:13:12,960 The answer we get is 588 kilograms. 186 00:13:12,960 --> 00:13:19,080 Now, a livestock expert guessed 584, so they're very close. 187 00:13:20,400 --> 00:13:21,600 But who's closest? 188 00:13:24,280 --> 00:13:27,560 It's time for the cow to reveal all. 189 00:13:27,560 --> 00:13:30,240 Haven't got her back legs in yet! Haven't got her back legs in. 190 00:13:34,520 --> 00:13:38,720 595 kilograms. Incredible! 191 00:13:38,720 --> 00:13:43,400 That's just seven kilograms higher than the group's estimate. 192 00:13:43,400 --> 00:13:47,640 The crowd got it just about spot-on, and they beat the experts. 193 00:13:49,120 --> 00:13:52,760 It seems many brains really are better than one, 194 00:13:52,760 --> 00:13:57,400 and that's due to something known as The Wisdom of the Crowd. 195 00:13:57,400 --> 00:14:00,880 Our highest guess was 1,400 kg, 196 00:14:00,880 --> 00:14:04,000 and our lowest 200 kg. 197 00:14:04,000 --> 00:14:06,360 So, both way off, 198 00:14:06,360 --> 00:14:10,000 but when a crowd works together the odd crazy guess 199 00:14:10,000 --> 00:14:11,600 doesn't really matter. 200 00:14:13,840 --> 00:14:16,920 And that works for nature, too. 201 00:14:16,920 --> 00:14:18,600 One animal might make a bad decision, 202 00:14:18,600 --> 00:14:23,080 but unless others have the same reaction, the swarm isn't fooled. 203 00:14:24,640 --> 00:14:28,000 That's why taking the option to ask the audience in a game show 204 00:14:28,000 --> 00:14:30,160 is such a smart move. 205 00:14:30,160 --> 00:14:32,800 They get it right about 90% of the time, 206 00:14:32,800 --> 00:14:37,440 compared with a 65% success rate from the experts. 207 00:14:38,640 --> 00:14:41,880 It's no wonder swarming has helped some creatures become 208 00:14:41,880 --> 00:14:44,080 the ultimate decision-makers. 209 00:14:46,040 --> 00:14:49,920 But not all swarms are about boosting brainpower. 210 00:14:49,920 --> 00:14:53,640 Some are about working together to solve a problem. 211 00:14:58,160 --> 00:15:01,240 The next stop on my journey is Christmas Islands, 212 00:15:01,240 --> 00:15:04,400 a tiny volcanic outcrop in the Indian Ocean. 213 00:15:08,920 --> 00:15:11,960 This dramatic, otherworldly landscape 214 00:15:11,960 --> 00:15:15,360 is the setting for an extraordinary swarm on the move. 215 00:15:17,640 --> 00:15:21,520 And right now is the best time to see it in action. 216 00:15:24,320 --> 00:15:27,200 Oh, my God, that is so... 217 00:15:28,840 --> 00:15:31,480 The island is about to go into lockdown. 218 00:15:35,120 --> 00:15:37,960 Every year as the monsoon rains arrive, 219 00:15:37,960 --> 00:15:42,640 60 million red crabs emerge out of the trees. 220 00:15:49,960 --> 00:15:52,760 A swarm facing the ultimate challenge. 221 00:16:00,960 --> 00:16:03,160 These land crabs live in a forest. 222 00:16:04,960 --> 00:16:07,080 But like their coastal ancestors, 223 00:16:07,080 --> 00:16:10,840 they're still completely dependent on the sea to breed. 224 00:16:14,120 --> 00:16:16,720 And between the forest and the beach 225 00:16:16,720 --> 00:16:19,960 lies a gruelling six-mile treck. 226 00:16:23,440 --> 00:16:27,040 This one is a female. 227 00:16:27,040 --> 00:16:28,920 You can see underneath... 228 00:16:30,320 --> 00:16:32,200 Gosh, she's really skittish. 229 00:16:32,200 --> 00:16:34,440 If I hold her very carefully you can see underneath 230 00:16:34,440 --> 00:16:37,680 that brown mass at the end of her abdomen under her tail, 231 00:16:37,680 --> 00:16:40,920 is something like 100,000 eggs. 232 00:16:40,920 --> 00:16:45,440 The reason that the females are a little more difficult to handle, 233 00:16:45,440 --> 00:16:48,640 they're much more flighty, is because all they've got 234 00:16:48,640 --> 00:16:52,120 on their mind just now is to get these eggs... 235 00:16:52,120 --> 00:16:55,360 Ow! ..into the sea as fast as they can. 236 00:16:55,360 --> 00:16:58,720 So that's what she has to do now, so I'm just going to let her... 237 00:16:58,720 --> 00:17:00,840 Oh, if I can get... 238 00:17:00,840 --> 00:17:03,000 ..get on her way. 239 00:17:03,000 --> 00:17:04,880 She knows exactly which way to go. 240 00:17:06,320 --> 00:17:09,760 The Christmas Islands crabs follow the same well-trodden route 241 00:17:09,760 --> 00:17:11,200 for generations. 242 00:17:17,720 --> 00:17:19,720 But the arrival of humans on the island 243 00:17:19,720 --> 00:17:23,040 has given them a few extra obstacles to deal with. 244 00:17:29,080 --> 00:17:32,080 But nothing can get in the way of their epic journey. 245 00:17:38,120 --> 00:17:41,840 In just over a week, the crabs will cover up to six miles. 246 00:17:43,880 --> 00:17:47,640 For a creature of this size that spends most of its life underground, 247 00:17:47,640 --> 00:17:50,920 that's like running several back-to-back marathons 248 00:17:50,920 --> 00:17:52,360 with no training. 249 00:17:56,760 --> 00:17:58,080 So how do they do it? 250 00:18:05,000 --> 00:18:07,480 Scientists have recently discovered 251 00:18:07,480 --> 00:18:10,760 it's all thanks to a special internal sugar reserve. 252 00:18:20,680 --> 00:18:23,560 Powered by a massive sugar rush once a year, 253 00:18:23,560 --> 00:18:25,440 these laidback forest creatures 254 00:18:25,440 --> 00:18:28,400 suddenly turn into long-distance athletes. 255 00:18:34,880 --> 00:18:38,520 Oh, my goodness! Look at this! This is... 256 00:18:40,200 --> 00:18:43,240 This is unbelievable. 257 00:18:43,240 --> 00:18:46,040 There's just crabs as far as the eye can see. 258 00:18:46,040 --> 00:18:48,880 Every inch of this rock is covered. 259 00:18:50,960 --> 00:18:55,680 Amazingly, after days of walking and dodging obstacles, 260 00:18:55,680 --> 00:18:59,280 tens of millions of crabs have survived and made it to the beach. 261 00:19:01,280 --> 00:19:04,720 Just in time for their next big challenge. 262 00:19:04,720 --> 00:19:06,080 Tonight's the night. 263 00:19:06,080 --> 00:19:09,840 They've got to shed their eggs on a pre-dawn high tide, 264 00:19:09,840 --> 00:19:13,080 when the difference between high and low tide is at the smallest, 265 00:19:13,080 --> 00:19:16,320 because if they fall in the sea, they drown, unbelievably. 266 00:19:16,320 --> 00:19:18,960 Being land crabs, they can't survive in the sea. 267 00:19:18,960 --> 00:19:20,960 But they've got to get their eggs in the sea. 268 00:19:23,240 --> 00:19:26,840 They all have just one tiny window of opportunity. 269 00:19:32,360 --> 00:19:34,800 And according to my calculations, 270 00:19:34,800 --> 00:19:37,240 that should be in about six hours' time. 271 00:19:39,680 --> 00:19:43,640 So, I'm taking my place with the crabs and waiting for high tide. 272 00:19:56,360 --> 00:20:00,400 It's 3am, and all around me female crabs have just started 273 00:20:00,400 --> 00:20:03,560 frantically scrambling to the edge of the surf. 274 00:20:11,280 --> 00:20:12,800 Well, this is it. 275 00:20:12,800 --> 00:20:15,000 The annual mass spawning has started, 276 00:20:15,000 --> 00:20:18,480 and it is just one of the most incredible things I've ever seen. 277 00:20:19,920 --> 00:20:25,000 It's easy to forget how treacherous this moment is for the crabs. 278 00:20:25,000 --> 00:20:28,080 Many of them will get washed away and drowned. 279 00:20:30,080 --> 00:20:33,360 But it's a risk they have to take. 280 00:20:33,360 --> 00:20:36,560 The crabs are actually spawning all around me. 281 00:20:36,560 --> 00:20:38,720 Every time they spawn, they put their claws up 282 00:20:38,720 --> 00:20:40,960 and they shake themselves, 283 00:20:40,960 --> 00:20:45,440 and as they do that they shed 100,000 eggs each. 284 00:20:49,160 --> 00:20:53,000 So many trillions of eggs have been shed into the Indian Ocean 285 00:20:53,000 --> 00:20:54,480 that it's turned into soup. 286 00:20:56,920 --> 00:21:02,360 That is just full of now freshly-hatched crab eggs. 287 00:21:05,640 --> 00:21:09,640 The minute they hit the seawater, the eggs hatch into tiny larvae. 288 00:21:10,840 --> 00:21:13,840 But now they're at the mercy of tides and currents. 289 00:21:16,000 --> 00:21:19,800 Most will end up as fish food or get swept away into deeper waters, 290 00:21:19,800 --> 00:21:21,200 never to be seen again. 291 00:21:22,880 --> 00:21:26,400 Which is why this swarm is so vital. 292 00:21:26,400 --> 00:21:29,600 To ensure the survival of just a few crabs, 293 00:21:29,600 --> 00:21:33,400 nature has to throw a lot of zeros at the problem. 294 00:21:33,400 --> 00:21:37,120 Over the next three days, something like three trillion 295 00:21:37,120 --> 00:21:42,160 individual crab larvae will be released into the Indian Ocean. 296 00:21:45,840 --> 00:21:50,080 But despite the incredible numbers, the baby crabs will only make it 297 00:21:50,080 --> 00:21:53,560 back to shore every six or seven years. 298 00:21:54,960 --> 00:21:58,160 And when they do, the scenes are spectacular. 299 00:22:01,280 --> 00:22:04,840 A super-swarm of tiny crabs defies the odds 300 00:22:04,840 --> 00:22:07,120 and climbs back out of the ocean. 301 00:22:10,120 --> 00:22:12,200 For a land crab trapped in a forest, 302 00:22:12,200 --> 00:22:15,840 this swarm has the ultimate survival strategy. 303 00:22:18,440 --> 00:22:19,560 And across the globe, 304 00:22:19,560 --> 00:22:24,200 there are similarly amazing sights as other swarms set off on the move. 305 00:22:26,320 --> 00:22:30,080 Individually, each animal has no idea which way they're heading. 306 00:22:31,440 --> 00:22:35,480 But as a group, somehow they all move in the same direction. 307 00:22:38,040 --> 00:22:41,120 But how do you get tens of millions of individuals 308 00:22:41,120 --> 00:22:43,680 to work together as a team? 309 00:22:45,360 --> 00:22:48,760 Well, strangely, it's all thanks to having nobody in charge. 310 00:22:51,440 --> 00:22:53,880 It might sound like a recipe for disaster, 311 00:22:53,880 --> 00:22:56,520 but if you look at a colony of leafcutter ants, 312 00:22:56,520 --> 00:22:58,760 everyone is doing their own thing. 313 00:23:01,200 --> 00:23:06,640 No single ant is in charge of organisation, not even the queen. 314 00:23:09,320 --> 00:23:11,920 But with every ant ignoring the bigger picture 315 00:23:11,920 --> 00:23:13,960 and focusing on the one job, 316 00:23:13,960 --> 00:23:17,320 the process actually becomes highly efficient. 317 00:23:20,680 --> 00:23:24,160 So, by thinking like ants, we're now changing the way 318 00:23:24,160 --> 00:23:27,320 we look at some of our own logistics. 319 00:23:29,000 --> 00:23:32,880 Every day, millions of us travel through the world's transport hubs. 320 00:23:34,760 --> 00:23:37,920 Getting from A to B by the most efficient route is vital 321 00:23:37,920 --> 00:23:40,120 to keeping things running smoothly. 322 00:23:41,400 --> 00:23:46,440 Something the ants do really well. So, how would they run an airport? 323 00:23:47,720 --> 00:23:51,560 By designing software capable of thinking like a swarm, 324 00:23:51,560 --> 00:23:52,960 we've been finding out. 325 00:23:54,440 --> 00:23:57,680 An American airline tried to solve a long-running debate - 326 00:23:57,680 --> 00:24:02,480 was it faster to board a plane by giving passengers allocated seating 327 00:24:02,480 --> 00:24:05,800 or by allowing them to pick their own seats? 328 00:24:05,800 --> 00:24:07,040 Surprisingly, 329 00:24:07,040 --> 00:24:11,480 when the computer programme used digital ants to fill the plane, 330 00:24:11,480 --> 00:24:14,960 it showed that sometimes, letting people choose their own seats 331 00:24:14,960 --> 00:24:17,400 is quicker than giving them seat numbers. 332 00:24:20,320 --> 00:24:23,600 Because when there's no top dog to make decisions for us, 333 00:24:23,600 --> 00:24:26,920 like the ants, we all have to think for ourselves, 334 00:24:26,920 --> 00:24:30,000 and it doesn't result in the chaos you'd expect. 335 00:24:34,440 --> 00:24:37,520 And new technology is taking this even further, 336 00:24:37,520 --> 00:24:40,120 with robots that use swarm intelligence. 337 00:24:43,960 --> 00:24:47,400 Just like insects, these robots all do their own thing. 338 00:24:52,720 --> 00:24:57,000 By reacting to each other, they can combine to do things 339 00:24:57,000 --> 00:24:58,800 that would be impossible on their own. 340 00:25:01,640 --> 00:25:04,320 The hope is that one day these robots could be sent out 341 00:25:04,320 --> 00:25:07,600 into some of our most dangerous locations. 342 00:25:07,600 --> 00:25:10,960 Artificial swarms working together on the front line, 343 00:25:10,960 --> 00:25:13,240 or on search and rescue missions, 344 00:25:13,240 --> 00:25:17,080 replacing humans and potentially saving lives. 345 00:25:18,920 --> 00:25:21,720 But while some swarms work together day after day, 346 00:25:23,400 --> 00:25:26,600 other swarms exist for only a few hours. 347 00:25:29,200 --> 00:25:31,720 Coordination is critical. 348 00:25:31,720 --> 00:25:34,960 Get it wrong, and your whole life has been wasted. 349 00:25:36,520 --> 00:25:40,440 This is a swarm that's seen on just a few nights of the year. 350 00:25:43,080 --> 00:25:45,480 Oh, my God! It's a blackout. 351 00:25:45,480 --> 00:25:46,920 GIRL SCREAMS 352 00:25:49,120 --> 00:25:52,440 Yes. They are alive. 353 00:25:55,480 --> 00:25:57,800 To be in with a chance of finding this swarm, 354 00:25:57,800 --> 00:26:00,920 I'm travelling to the States, to Wisconsin. 355 00:26:05,880 --> 00:26:09,720 I'm chasing a massive swarm that appears from nowhere, 356 00:26:09,720 --> 00:26:13,200 so this part of my journey will be a race against time. 357 00:26:15,360 --> 00:26:17,960 To get a sense of the challenge ahead, 358 00:26:17,960 --> 00:26:20,800 I've come to the local weather centre in La Crosse, 359 00:26:20,800 --> 00:26:25,400 where they've been keeping a close eye on the swarm's past movements. 360 00:26:25,400 --> 00:26:29,280 That is just incredible! It's like an explosion. 361 00:26:29,280 --> 00:26:32,040 Right, this was just after sundown. 362 00:26:32,040 --> 00:26:35,480 Some biological target is coming out of the river 363 00:26:35,480 --> 00:26:38,960 and then being carried by the wind away from the Mississippi River. 364 00:26:38,960 --> 00:26:41,400 If I could see that, if that happened again, 365 00:26:41,400 --> 00:26:43,800 or even anything remotely like that... 366 00:26:43,800 --> 00:26:46,640 I would be very, very happy. 367 00:26:48,360 --> 00:26:53,560 So, what swarm could be so intense that it shows up on weather radars? 368 00:26:59,640 --> 00:27:03,080 Well, for just a few days every summer, amazingly, millions, 369 00:27:03,080 --> 00:27:08,640 some say trillions of mayflies take to the sky to form dense clouds. 370 00:27:10,840 --> 00:27:14,240 It's a blizzard of insects thick enough to stop traffic. 371 00:27:16,720 --> 00:27:20,920 But despite the massive size of this swarm, it's unpredictable, 372 00:27:20,920 --> 00:27:22,880 so finding it won't be easy. 373 00:27:25,240 --> 00:27:28,720 Time for me to take to the airways. 374 00:27:28,720 --> 00:27:32,000 Well, I'm in the right place and it's more or less the right time. 375 00:27:32,000 --> 00:27:34,000 But if I'm going to see a really big swarm, 376 00:27:34,000 --> 00:27:37,200 I've got an idea of how I can enlist some local help. 377 00:27:38,480 --> 00:27:43,920 Downtown La Crosse. It's now 14.10. WIZM. 378 00:27:45,360 --> 00:27:48,200 I'm George McGavin and we're from the BBC. 379 00:27:48,200 --> 00:27:50,880 RADIO DJ: Swarms of mayflies have attracted the attention 380 00:27:50,880 --> 00:27:55,120 of famed entomologist and TV host George McGavin. 381 00:27:55,120 --> 00:27:57,560 For a lot of people around here it's going to be surprising 382 00:27:57,560 --> 00:27:59,800 to hear that you want to be in the swarm. When we see 383 00:27:59,800 --> 00:28:01,840 those swarms we want to get in our car, get inside 384 00:28:01,840 --> 00:28:03,960 and get away from it. Why? It's fantastic. 385 00:28:03,960 --> 00:28:08,000 For an insect to be able to halt a train or a car, you know, 386 00:28:08,000 --> 00:28:09,360 that's pretty special. 387 00:28:09,360 --> 00:28:11,320 That's something I really want to see. 388 00:28:14,360 --> 00:28:16,120 We just need mayflies, lots of them. 389 00:28:16,120 --> 00:28:19,520 And they can call any time, day or night? Absolutely. We'll be there. 390 00:28:19,520 --> 00:28:21,520 We'll be hot on the heels of the swarm. 391 00:28:30,680 --> 00:28:34,160 I just hope we get the phone calls. I just hope we get folks ringing. 392 00:28:34,160 --> 00:28:36,360 We've done what we can, 393 00:28:36,360 --> 00:28:40,200 but it's impossible to predict where the first sighting will come from. 394 00:28:42,000 --> 00:28:43,440 One thing we do know is, 395 00:28:43,440 --> 00:28:47,920 they all start off in the same place - the Mississippi River. 396 00:28:50,160 --> 00:28:53,600 Mayflies spend most of their lives hidden underwater. 397 00:28:54,560 --> 00:28:56,040 So by looking in the river, 398 00:28:56,040 --> 00:28:59,520 I should be able to get right to the source of this swarm. 399 00:29:00,680 --> 00:29:03,360 So now, hopefully, in here 400 00:29:03,360 --> 00:29:06,400 are one or two or more mayfly nymphs. 401 00:29:09,280 --> 00:29:13,160 In a good year, a grab of that size might contain 15 nymphs, 402 00:29:13,160 --> 00:29:15,560 and if you think of that, it's a very small area 403 00:29:15,560 --> 00:29:18,000 and if you multiply it by this vast area, 404 00:29:18,000 --> 00:29:22,120 that's the sort of volumes of animals that we're hunting for. 405 00:29:22,120 --> 00:29:23,600 Oh, here, we got one. 406 00:29:25,120 --> 00:29:26,440 So, that's what we're after. 407 00:29:26,440 --> 00:29:27,960 This is a mayfly nymph, 408 00:29:27,960 --> 00:29:31,800 and they're perfectly adapted for existing in silt. 409 00:29:31,800 --> 00:29:34,440 They're very streamlined. They've got two tusks 410 00:29:34,440 --> 00:29:37,080 at the front of the head for excavating through the mud. 411 00:29:37,080 --> 00:29:39,920 They've got these really strong front legs, as well, 412 00:29:39,920 --> 00:29:42,240 which have little sort of prongs on them. 413 00:29:42,240 --> 00:29:45,000 So they are the perfect silt inhabitants, 414 00:29:45,000 --> 00:29:48,560 and they stay there for perhaps a year, up to two years... 415 00:29:49,680 --> 00:29:53,920 Until all conditions are right to trigger a mass emergence. 416 00:29:55,160 --> 00:29:58,400 It's thought water temperature has a lot to do with it, 417 00:29:58,400 --> 00:30:01,440 but lots of other factors like weather and food supply 418 00:30:01,440 --> 00:30:04,120 also play a role, 419 00:30:04,120 --> 00:30:09,560 making it frustratingly difficult to predict what's going on down there. 420 00:30:09,560 --> 00:30:11,560 Unless you're a mayfly, that is. 421 00:30:17,720 --> 00:30:21,360 With just 24 hours to emerge, find a mate, breed 422 00:30:21,360 --> 00:30:23,600 and get back to the river, 423 00:30:23,600 --> 00:30:26,200 it's a race against time for survival. 424 00:30:27,320 --> 00:30:29,120 Miss it by just a few hours, 425 00:30:29,120 --> 00:30:32,920 and you'll miss your one and only chance to find a mate. 426 00:30:36,720 --> 00:30:39,040 And I'm racing against the clock, too. 427 00:30:41,080 --> 00:30:44,320 Time to get back out on the road and keep looking. 428 00:30:46,800 --> 00:30:50,200 A swarm of mayflies could form anywhere along the river. 429 00:30:51,240 --> 00:30:53,840 But towns and roads are a good place to start looking 430 00:30:53,840 --> 00:30:57,480 because there's one thing they just can't seem to resist. 431 00:30:58,520 --> 00:30:59,760 Lights. 432 00:31:01,480 --> 00:31:02,920 The brighter, the better. 433 00:31:06,480 --> 00:31:10,280 So our shiny new modern lights play havoc with them, 434 00:31:10,280 --> 00:31:13,160 and bring chaos to our towns. 435 00:31:16,680 --> 00:31:20,840 It could be that the lights are a giant mayfly singles bar. 436 00:31:22,480 --> 00:31:24,600 With just hours to breed, 437 00:31:24,600 --> 00:31:28,160 there's not much time to fly about and look for a mate. 438 00:31:29,160 --> 00:31:31,400 So, by all heading to the nearest bright light, 439 00:31:31,400 --> 00:31:34,440 you improve your chances of finding a partner. 440 00:31:37,600 --> 00:31:39,600 And just as I was about to give up hope 441 00:31:39,600 --> 00:31:42,440 of getting to see this incredible event in action, 442 00:31:42,440 --> 00:31:44,200 there's some promising news. 443 00:31:46,920 --> 00:31:51,520 I've just had a phone call from a boat yard up here. 444 00:31:51,520 --> 00:31:54,520 This looks like the marina, 445 00:31:54,520 --> 00:31:56,240 so I hope I'm in the right place. 446 00:31:57,840 --> 00:31:59,840 Oh! Oh-ho! 447 00:32:00,920 --> 00:32:03,560 Mayflies, flying. Look, there's one on the window. 448 00:32:03,560 --> 00:32:06,040 Whoa, this is more like it. 449 00:32:06,040 --> 00:32:08,440 Whoa! Look at this! 450 00:32:08,440 --> 00:32:11,440 'We've caught the very beginnings of a swarm.' 451 00:32:13,520 --> 00:32:16,520 These guys will have left the river late last night last night, 452 00:32:16,520 --> 00:32:18,760 looking for a landing spot 453 00:32:18,760 --> 00:32:21,840 where they can go through one final transformation. 454 00:32:23,280 --> 00:32:24,880 This is incredible. 455 00:32:24,880 --> 00:32:29,880 This is the emergence of an adult mayfly from the sub-adult, 456 00:32:29,880 --> 00:32:34,600 and this is a process that has been going on for 300 million years. 457 00:32:36,240 --> 00:32:37,840 This is incredible to watch. 458 00:32:38,960 --> 00:32:41,960 Now, it's still got to get the end of its abdomen out, 459 00:32:41,960 --> 00:32:45,280 and it's got to draw out those long tails. 460 00:32:46,600 --> 00:32:50,800 And this exact process is being repeated 461 00:32:50,800 --> 00:32:52,680 hundreds of millions of times. 462 00:33:04,400 --> 00:33:05,720 In a few hours' time, 463 00:33:05,720 --> 00:33:09,640 all the new adults will rise into the air in a huge swarm. 464 00:33:12,400 --> 00:33:16,480 The mayfly have spent their entire lives in the mud, 465 00:33:16,480 --> 00:33:19,520 waiting for this brief and all-important moment. 466 00:33:23,880 --> 00:33:26,960 By evening, the sky fills with millions of them, 467 00:33:26,960 --> 00:33:29,320 in an intense breeding frenzy. 468 00:33:32,320 --> 00:33:36,120 Being part of the swarm is a once in a lifetime event for the mayfly. 469 00:33:37,800 --> 00:33:42,680 But other insects have to deal with a whole life in amongst the swarm. 470 00:33:42,680 --> 00:33:46,320 But then working together efficiently, is vital. 471 00:33:51,080 --> 00:33:54,200 Ant colonies are completely dependent on keeping the supplies 472 00:33:54,200 --> 00:33:55,960 coming in thick and fast. 473 00:33:58,520 --> 00:34:00,560 With millions of hungry mouths to feed, 474 00:34:00,560 --> 00:34:02,560 any delay could be a disaster. 475 00:34:05,440 --> 00:34:10,040 So, they avoid a crisis by following a surprising highway code. 476 00:34:11,920 --> 00:34:16,280 To go as fast as possible, the ants have learned to slow down. 477 00:34:18,640 --> 00:34:21,920 That means no boy racers and no overtaking. 478 00:34:24,520 --> 00:34:27,840 And what works for the ants also works for us. 479 00:34:29,800 --> 00:34:33,560 Twice a day, our roads have to cope with millions of people 480 00:34:33,560 --> 00:34:36,280 all trying to be at the right place at the right time. 481 00:34:39,120 --> 00:34:43,080 Designing our transport networks to cope is a huge challenge. 482 00:34:44,880 --> 00:34:46,840 So, now, our road planners 483 00:34:46,840 --> 00:34:50,080 are starting to pick up a few tips from the ants. 484 00:34:57,000 --> 00:35:00,880 By restricting each and every car to around 50 miles an hour, 485 00:35:00,880 --> 00:35:02,920 actually makes the journey faster. 486 00:35:03,960 --> 00:35:05,960 And although it might not seem like it, 487 00:35:05,960 --> 00:35:07,760 reducing the number of lanes 488 00:35:07,760 --> 00:35:11,240 and banning overtaking makes things even more efficient. 489 00:35:14,440 --> 00:35:17,360 And now several car companies are taking this a step further 490 00:35:17,360 --> 00:35:20,800 by looking into technology that keeps cars 491 00:35:20,800 --> 00:35:23,960 close behind each other and at a constant speed... 492 00:35:24,880 --> 00:35:27,000 ..just like the travelling ants. 493 00:35:28,880 --> 00:35:30,920 That is just weird. 494 00:35:30,920 --> 00:35:34,320 These super-smart cars have sensors that read their speed 495 00:35:34,320 --> 00:35:37,400 and distance from the vehicle in front. 496 00:35:37,400 --> 00:35:40,080 I'm not touching the brake at all. 497 00:35:40,080 --> 00:35:43,480 All you have to do is hold the wheel and, if that car in front stops, 498 00:35:43,480 --> 00:35:46,360 the brakes are applied automatically... 499 00:35:46,360 --> 00:35:47,880 bringing me to a halt. 500 00:35:50,240 --> 00:35:53,840 I have to say, it really makes you very nervous. 501 00:35:53,840 --> 00:35:56,320 It's a very unsettling feeling 502 00:35:56,320 --> 00:35:59,360 not to be in control of the car, as it were. 503 00:36:01,000 --> 00:36:02,600 Stopping here - oh. 504 00:36:02,600 --> 00:36:05,280 Oh. Oh. 505 00:36:05,280 --> 00:36:07,840 Oh. HE LAUGHS 506 00:36:07,840 --> 00:36:09,520 I didn't touch the brake. 507 00:36:11,760 --> 00:36:13,760 Oh, my goodness. 508 00:36:13,760 --> 00:36:15,760 These cars are so clever that even 509 00:36:15,760 --> 00:36:18,280 when the car in front brakes unexpectedly, 510 00:36:18,280 --> 00:36:21,840 the car has everything under control. 511 00:36:21,840 --> 00:36:23,000 Ah! 512 00:36:23,000 --> 00:36:24,120 Oh! 513 00:36:25,360 --> 00:36:29,600 Oh! 514 00:36:29,600 --> 00:36:30,600 Ah! 515 00:36:30,600 --> 00:36:32,680 Let me just get my breath back now. 516 00:36:36,400 --> 00:36:38,760 HE SIGHS That was unbelievable. 517 00:36:41,000 --> 00:36:44,840 I'm not sure I'm quite ready for a car with swarm powers 518 00:36:44,840 --> 00:36:46,360 but it's a genius idea. 519 00:36:47,720 --> 00:36:51,520 And with almost 40 million vehicles on UK roads, 520 00:36:51,520 --> 00:36:55,200 technology like this could be the answer to keeping traffic 521 00:36:55,200 --> 00:36:57,640 flowing with ant-like precision. 522 00:37:04,800 --> 00:37:08,240 But while some swarms are helping us overcome problems, 523 00:37:08,240 --> 00:37:11,840 others are just adding to them. 524 00:37:11,840 --> 00:37:15,920 In America, there's an unseen swarm that has silently invaded 525 00:37:15,920 --> 00:37:17,760 and is slowly taking over. 526 00:37:21,360 --> 00:37:24,280 In the last 40 years, it's spread into 23 states 527 00:37:24,280 --> 00:37:26,800 and yet remains largely hidden from view. 528 00:37:28,360 --> 00:37:33,680 The American government has spend over $150m trying to control it. 529 00:37:35,040 --> 00:37:38,480 It's a swarm that I have never experienced before 530 00:37:38,480 --> 00:37:41,760 and one that is not without considerable risk. 531 00:37:46,760 --> 00:37:48,680 For my chance to meet this swarm, 532 00:37:48,680 --> 00:37:52,080 I'm heading to Bath, Illinois, in the American Midwest. 533 00:37:55,560 --> 00:37:57,800 And it seems I'm not the only one 534 00:37:57,800 --> 00:38:00,840 here to meet this highly destructive swarm. 535 00:38:02,040 --> 00:38:05,040 There was a couple of guys that got black eyes that got hit in the face 536 00:38:05,040 --> 00:38:07,640 with no protection, and they're walking around here today. 537 00:38:07,640 --> 00:38:08,960 They got a big, old shiner. 538 00:38:08,960 --> 00:38:11,200 That looks painful. It was. 539 00:38:11,200 --> 00:38:14,880 This one was the first hit yesterday and one on this eye. 540 00:38:14,880 --> 00:38:17,600 And you're back for more. Back for more. This is dangerous. 541 00:38:17,600 --> 00:38:19,480 Yeah. We've been coming eight years. 542 00:38:19,480 --> 00:38:22,160 This is the first time we've ever got hurt, though. 543 00:38:23,560 --> 00:38:26,000 People say they eat them but, as nasty as they look, 544 00:38:26,000 --> 00:38:27,040 I ain't touching them. 545 00:38:28,680 --> 00:38:31,080 Just what have I let myself in for? 546 00:38:36,800 --> 00:38:40,840 To find out, the Illinois Natural History Team is going to get me 547 00:38:40,840 --> 00:38:43,600 face-to-face with the problem. 548 00:38:43,600 --> 00:38:46,840 Today, we're going to use a technique called electrofishing, 549 00:38:46,840 --> 00:38:50,600 and we're going to put anywhere from 4,500 to 5,000 volts into the water. 550 00:38:58,320 --> 00:39:00,880 Well, this is the calm before the swarm. 551 00:39:00,880 --> 00:39:02,840 I have no idea what's going to happen. 552 00:39:10,880 --> 00:39:13,560 Wow! 553 00:39:13,560 --> 00:39:14,920 This is crazy! 554 00:39:17,440 --> 00:39:19,240 Argh! 555 00:39:19,240 --> 00:39:21,680 That is unbelievable. 556 00:39:21,680 --> 00:39:23,320 Oh! 557 00:39:23,320 --> 00:39:26,960 This is what I'm here for, the Asian silver carp, 558 00:39:26,960 --> 00:39:31,640 a fish with a unique panic reflex, causing it to leap out of the water. 559 00:39:32,840 --> 00:39:35,520 There are literally thousands of these carp. 560 00:39:35,520 --> 00:39:36,960 Arg! 561 00:39:36,960 --> 00:39:38,560 This is absolute insanity. 562 00:39:42,000 --> 00:39:46,280 Whether it's a predator, a boat or our electric current, 563 00:39:46,280 --> 00:39:49,920 a reflex response spreads through the swarm, 564 00:39:49,920 --> 00:39:52,760 setting off a chain reaction of leaping fish. 565 00:39:55,560 --> 00:39:57,240 It's a vital way of measuring 566 00:39:57,240 --> 00:39:59,640 just how many fish are lurking down there. 567 00:40:01,320 --> 00:40:06,760 At the moment, the best guess is 2,500 carp per mile of river 568 00:40:06,760 --> 00:40:08,800 but the numbers are still growing. 569 00:40:10,320 --> 00:40:12,440 And as carp numbers are going up, 570 00:40:12,440 --> 00:40:15,000 the amount of other wildlife is going down. 571 00:40:17,360 --> 00:40:20,800 I've never seen so much fish in my life. 572 00:40:20,800 --> 00:40:23,240 Oh! 573 00:40:23,240 --> 00:40:27,200 This is a swarm out of control and ecologically dangerous. 574 00:40:30,360 --> 00:40:33,840 Getting rid of it isn't going to be easy, but the battle is on. 575 00:40:35,640 --> 00:40:39,040 The big concern is that the carp are only 50 miles away 576 00:40:39,040 --> 00:40:41,200 from the great lakes of America. 577 00:40:42,440 --> 00:40:44,760 If they continue to spread in that direction, 578 00:40:44,760 --> 00:40:47,600 they could devastate a $4bn fishing industry. 579 00:40:49,240 --> 00:40:54,240 The US government have been spending $150m in the last two years 580 00:40:54,240 --> 00:40:56,440 just to control this species. 581 00:40:56,440 --> 00:40:58,040 Everybody all right? 582 00:40:58,040 --> 00:40:59,360 I got one on the backside. 583 00:41:01,360 --> 00:41:03,200 Unbelievable. 584 00:41:07,560 --> 00:41:12,160 So far, they've tried everything from poison to electric barriers, 585 00:41:12,160 --> 00:41:14,960 but nothing seems to be able to stop the carp. 586 00:41:20,200 --> 00:41:23,360 So, the locals have decided to take matters into their own hands. 587 00:41:28,520 --> 00:41:31,720 This fishing tournament is their chance to fight back. 588 00:41:31,720 --> 00:41:35,000 We're now in the middle of this fishing chaos. 589 00:41:35,000 --> 00:41:39,040 There's about 50 boats here. There's some more boats coming towards us. 590 00:41:41,040 --> 00:41:43,480 Whoa! That hit him right on the head, that. 591 00:41:45,040 --> 00:41:47,240 Carnage! 592 00:41:47,240 --> 00:41:48,560 Oh, jeez! 593 00:41:49,640 --> 00:41:51,080 HE LAUGHS 594 00:41:51,080 --> 00:41:52,840 I'm hanging on. 595 00:41:52,840 --> 00:41:55,800 But why have the carp got out of control? 596 00:41:57,600 --> 00:41:58,680 Ooh! 597 00:42:01,080 --> 00:42:04,200 They eat algae and because they eat so much of it, 598 00:42:04,200 --> 00:42:06,640 they are basically eating all of the food 599 00:42:06,640 --> 00:42:08,840 that the fish here would normally eat. 600 00:42:11,320 --> 00:42:14,640 The carp can eat up to a third of their body weight a day. 601 00:42:16,200 --> 00:42:19,000 Their ferocious appetite has pretty much emptied 602 00:42:19,000 --> 00:42:21,080 the river of food for anything else. 603 00:42:24,480 --> 00:42:27,360 This swarm is taking over. 604 00:42:27,360 --> 00:42:31,200 And the trouble with all this is, it's a purely man-made problem. 605 00:42:31,200 --> 00:42:34,040 These fish were introduced 40 years ago to clean 606 00:42:34,040 --> 00:42:36,840 the algae off commercial catfish ponds. 607 00:42:39,320 --> 00:42:41,480 When they escaped into nearby rivers, 608 00:42:41,480 --> 00:42:44,400 the carp found themselves in the river full of food 609 00:42:44,400 --> 00:42:46,400 and nothing to stand in their way. 610 00:42:48,280 --> 00:42:52,360 With each carp able to produce up to two million eggs a year, 611 00:42:52,360 --> 00:42:55,960 it didn't take long for the fish to become a swarm. 612 00:42:57,560 --> 00:43:01,080 Something that doesn't happen back in their native home, Asia, 613 00:43:01,080 --> 00:43:03,560 where predators keep their numbers in check. 614 00:43:04,720 --> 00:43:09,400 They've just exploded. This is a swarm of epic proportions. 615 00:43:10,600 --> 00:43:13,080 Look at the size of that one. 616 00:43:13,080 --> 00:43:15,080 That's got to be 30 pounds. 617 00:43:16,320 --> 00:43:18,520 If that hit you, it would break your jaw. 618 00:43:20,960 --> 00:43:24,200 PEOPLE SHOUT 619 00:43:32,760 --> 00:43:35,560 And although this may all look a bit unconventional, 620 00:43:35,560 --> 00:43:39,160 this event does play a small part in a serious attempt 621 00:43:39,160 --> 00:43:40,800 to control these fish. 622 00:43:46,640 --> 00:43:47,960 By the end of the event, 623 00:43:47,960 --> 00:43:51,000 over two tons of carp will have been cleared from the river. 624 00:43:53,040 --> 00:43:54,720 ALL CHEER 625 00:43:54,720 --> 00:43:57,840 And that's in addition to the hundreds of tons caught 626 00:43:57,840 --> 00:44:00,320 every year through commercial fishing, 627 00:44:00,320 --> 00:44:03,400 some of which is actually now exported back as food 628 00:44:03,400 --> 00:44:05,040 to the carp's original home, Asia. 629 00:44:07,280 --> 00:44:10,520 But all this is just keeping things in check. 630 00:44:10,520 --> 00:44:14,600 It's not enough to actually defeat the swarm and stop it spreading... 631 00:44:17,640 --> 00:44:20,920 Because a dangerous combination of unlimited food, 632 00:44:20,920 --> 00:44:25,920 lots of space and freedom from predators allows some animals 633 00:44:25,920 --> 00:44:28,320 to swarm to biblical proportions. 634 00:44:30,240 --> 00:44:34,600 And when swarms get to this scale, they also have a dark side. 635 00:44:37,240 --> 00:44:39,560 It doesn't take much to throw hundreds 636 00:44:39,560 --> 00:44:41,400 of carp into mass confusion. 637 00:44:43,840 --> 00:44:47,920 In seconds, fear passes from fish to fish... 638 00:44:47,920 --> 00:44:50,800 even though most of them won't know what they're afraid of. 639 00:44:55,040 --> 00:44:58,280 Because in a swarm, individuals are so closely connected 640 00:44:58,280 --> 00:45:00,200 that they share moods and reactions. 641 00:45:11,080 --> 00:45:14,520 In the event of danger, a quick, united response like this 642 00:45:14,520 --> 00:45:16,920 can mean the difference between life or death. 643 00:45:19,400 --> 00:45:22,560 But, occasionally, the system goes wrong. 644 00:45:31,560 --> 00:45:34,400 An event sends a contagious emotion through the swarm 645 00:45:34,400 --> 00:45:35,840 and causes complete chaos. 646 00:45:44,000 --> 00:45:47,200 And, unfortunately, that's something you see in humans, too. 647 00:45:49,040 --> 00:45:51,480 CHEERING 648 00:45:51,480 --> 00:45:55,320 When thousands of strangers come together for a shared experience, 649 00:45:55,320 --> 00:45:58,200 it can create a powerful connection. 650 00:46:01,360 --> 00:46:05,000 When everything's going well, it can be an incredible experience. 651 00:46:05,000 --> 00:46:08,120 But when the mood changes, things can get very nasty. 652 00:46:10,240 --> 00:46:12,600 It takes just one event to cause a crowd 653 00:46:12,600 --> 00:46:15,040 to stampede like wildebeest... 654 00:46:15,040 --> 00:46:17,760 out of control and with dangerous consequences. 655 00:46:17,760 --> 00:46:20,760 SIREN BLARES 656 00:46:20,760 --> 00:46:24,320 Anger spreads person to person till a peaceful demonstration 657 00:46:24,320 --> 00:46:26,200 becomes a full-blown mob. 658 00:46:27,520 --> 00:46:30,920 People stop thinking as individuals and begin to follow the herd. 659 00:46:31,960 --> 00:46:36,800 Emotions are high and behaviour starts to change. 660 00:46:36,800 --> 00:46:41,080 Within the group, people start losing their inhibitions. 661 00:46:41,080 --> 00:46:44,280 They do things they'd never consider doing if they were on their own. 662 00:46:45,760 --> 00:46:48,760 And because the group makes individuals feel powerful 663 00:46:48,760 --> 00:46:50,320 and less accountable, 664 00:46:50,320 --> 00:46:54,120 normally responsible people start acting completely out of character. 665 00:46:57,480 --> 00:46:59,120 So, finding yourself in a crowd 666 00:46:59,120 --> 00:47:01,760 can play a huge role in how you behave as an individual. 667 00:47:01,760 --> 00:47:02,760 SIREN BLARES 668 00:47:05,440 --> 00:47:08,960 Now, thankfully, most human gatherings pass without incident. 669 00:47:10,480 --> 00:47:14,240 But there is a swarm where big crowds are nearly always fatal. 670 00:47:18,840 --> 00:47:22,440 A plague of locusts is never a welcome sight for farmers. 671 00:47:24,360 --> 00:47:28,360 But when the numbers explode, it's also bad news for the swarm. 672 00:47:31,280 --> 00:47:35,680 At peak populations, the locusts suddenly start craving protein... 673 00:47:37,120 --> 00:47:40,240 ..and the meat closest to hand is the insect ahead. 674 00:47:41,800 --> 00:47:45,000 To avoid being eaten alive by their nearest neighbours, 675 00:47:45,000 --> 00:47:46,840 the locusts need to keep moving. 676 00:47:48,240 --> 00:47:51,560 This cannibalistic swarm is not just tearing through the crops, 677 00:47:51,560 --> 00:47:54,600 it's also at risk of devouring itself. 678 00:47:56,600 --> 00:48:00,960 But overcrowding doesn't always work against the swarm. 679 00:48:00,960 --> 00:48:03,280 The animal I'm off to see next has turned 680 00:48:03,280 --> 00:48:06,080 overcrowding into its greatest asset. 681 00:48:11,800 --> 00:48:14,280 This is a creature found in numbers so high, 682 00:48:14,280 --> 00:48:16,920 it brings people out into the streets. 683 00:48:18,520 --> 00:48:21,000 To join them, I'm heading south. 684 00:48:30,160 --> 00:48:32,560 I'm in Texas, home to the largest gathering 685 00:48:32,560 --> 00:48:34,440 of mammals anywhere on the planet. 686 00:48:36,440 --> 00:48:39,720 Every summer, as night falls in Austin, Texas, 687 00:48:39,720 --> 00:48:42,280 a seemingly endless swarm fills the air. 688 00:48:45,600 --> 00:48:49,240 Wow! Look at this. They're just like flooding out of the bridge right now. 689 00:48:55,520 --> 00:48:58,120 Wow! Look back into the distance, guys. 690 00:48:58,120 --> 00:48:59,880 It almost looks like a plume of smoke. 691 00:48:59,880 --> 00:49:02,480 The residents are outnumbered. 692 00:49:02,480 --> 00:49:05,480 Over a million creatures are swarming the skies. 693 00:49:15,440 --> 00:49:17,880 This bridge is the biggest urban roost 694 00:49:17,880 --> 00:49:21,200 for Mexican free-tailed bats anywhere in the world. 695 00:49:23,160 --> 00:49:25,360 Oh, look at this. Look at this. 696 00:49:25,360 --> 00:49:26,920 This has become a real spectacle. 697 00:49:30,680 --> 00:49:32,880 There's just hundreds of thousands of bats 698 00:49:32,880 --> 00:49:35,240 and they're streaming out from under the bridge. 699 00:49:35,240 --> 00:49:37,760 This is a colony of biblical proportions. 700 00:49:41,920 --> 00:49:46,520 So what do the bright lights of the city have to offer these bats? 701 00:49:46,520 --> 00:49:48,160 Like many riverside cities, 702 00:49:48,160 --> 00:49:50,760 there's a glut of insects in the summer months. 703 00:49:53,080 --> 00:49:57,040 But what really makes Austin a bat hotspot is its architecture. 704 00:49:58,640 --> 00:50:01,400 When Congress Bridge was rebuilt in the '80s, 705 00:50:01,400 --> 00:50:04,600 the new structure was full of deep, narrow openings. 706 00:50:06,840 --> 00:50:11,680 It was the ideal bat home and they moved in en masse, 707 00:50:11,680 --> 00:50:14,960 but this convenient city pad isn't without problems. 708 00:50:19,440 --> 00:50:22,120 Space is limited and the bats are an easy target 709 00:50:22,120 --> 00:50:25,960 for birds of prey and other predators. 710 00:50:53,880 --> 00:50:56,200 So, as impressive as this is, 711 00:50:56,200 --> 00:51:01,240 a three-hour drive away, there's a bat swarm ten times bigger. 712 00:51:06,160 --> 00:51:10,400 And a swarm of this size can achieve the seemingly impossible. 713 00:51:15,840 --> 00:51:19,320 But getting a good view of it isn't going to be easy. 714 00:51:22,400 --> 00:51:24,640 This area of Texas is riddled with caves, 715 00:51:24,640 --> 00:51:27,040 making it the perfect habitat for bats. 716 00:51:28,400 --> 00:51:32,760 The caves offer them protection from the elements and from aerial attack. 717 00:51:34,760 --> 00:51:36,400 But to find the real reason 718 00:51:36,400 --> 00:51:39,440 ten million bats flock to this particular cave... 719 00:51:40,880 --> 00:51:43,480 I need to get much closer to the swarm. 720 00:51:45,120 --> 00:51:48,400 This isn't going to be a pleasant journey. 721 00:51:48,400 --> 00:51:51,200 I'm now entering one of the most overcrowded 722 00:51:51,200 --> 00:51:52,880 and toxic places on Earth. 723 00:51:54,880 --> 00:51:56,400 So, I've come prepared. 724 00:52:00,760 --> 00:52:03,000 Wow. The smell. 725 00:52:03,000 --> 00:52:06,200 Ammonia is actually quite intense. 726 00:52:08,920 --> 00:52:11,960 The caves are piled high with bat droppings, guano, 727 00:52:11,960 --> 00:52:15,400 releasing dangerously high levels of poisonous gases. 728 00:52:18,680 --> 00:52:22,680 Levels of ammonia are so high that it bleaches the bats' fur. 729 00:52:24,120 --> 00:52:28,200 But, amazingly, the bats themselves aren't harmed. 730 00:52:28,200 --> 00:52:30,080 By slowing down their metabolism, 731 00:52:30,080 --> 00:52:33,000 their bodies are able to neutralise the toxic gas. 732 00:52:40,040 --> 00:52:42,800 This pile of guano is absolutely enormous - 733 00:52:42,800 --> 00:52:45,760 it must be metres thick. 734 00:52:45,760 --> 00:52:49,400 That roof is absolutely jam-packed with bats and look at them. 735 00:52:50,640 --> 00:52:52,840 It's every crevice. 736 00:52:52,840 --> 00:52:54,960 There's a big group of them right here. 737 00:52:57,640 --> 00:53:01,360 The levels of ammonia are now potentially fatal 738 00:53:01,360 --> 00:53:05,360 and, without these masks, we'd be unconscious in a matter of minutes. 739 00:53:06,560 --> 00:53:10,840 Very little can survive these lethal conditions... 740 00:53:10,840 --> 00:53:12,480 apart from the bats, that is. 741 00:53:14,320 --> 00:53:17,960 If you're wondering what a million bats look like, it looks like this. 742 00:53:17,960 --> 00:53:21,160 This is one of the most incredible sights I think I've ever seen. 743 00:53:27,280 --> 00:53:30,080 This is a giant bat creche. 744 00:53:31,840 --> 00:53:35,000 Every year, ten million pregnant female bats 745 00:53:35,000 --> 00:53:37,280 fly to these caves to give birth. 746 00:53:39,080 --> 00:53:43,720 It's more or less predator-free down here, thanks to the deadly fumes, 747 00:53:43,720 --> 00:53:46,400 so it's a safe place for mothers to leave their young 748 00:53:46,400 --> 00:53:47,920 while they go off and hunt. 749 00:53:49,120 --> 00:53:52,040 The really amazing thing about these bats is, 750 00:53:52,040 --> 00:53:55,480 the adult females roost in a different part of the cave. 751 00:53:55,480 --> 00:53:58,000 These are just the young and so to feed them, 752 00:53:58,000 --> 00:54:01,680 they have to actually find their own individual flock 753 00:54:01,680 --> 00:54:03,200 in amongst this lot. 754 00:54:03,200 --> 00:54:05,680 Just imagine you having to find your baby 755 00:54:05,680 --> 00:54:08,280 in among a million other close-packed babies. 756 00:54:08,280 --> 00:54:09,800 It's just unbelievable. 757 00:54:13,880 --> 00:54:15,760 But there's something even smarter 758 00:54:15,760 --> 00:54:17,800 about how these baby bats are organised. 759 00:54:20,320 --> 00:54:24,160 They're crammed in at over 4,000 bats per square metre, 760 00:54:25,200 --> 00:54:28,440 and it's this incredible density of animals that holds the key 761 00:54:28,440 --> 00:54:30,480 to their success. 762 00:54:30,480 --> 00:54:33,720 I've brought a thermal imaging camera, which will show us 763 00:54:33,720 --> 00:54:36,600 which parts of the cave are hot. 764 00:54:36,600 --> 00:54:39,120 So, if I pan the thermal image camera across the roof, 765 00:54:39,120 --> 00:54:41,240 you can see it's not very hot. 766 00:54:41,240 --> 00:54:44,720 And then when I get to the roof - look at that. 767 00:54:44,720 --> 00:54:48,360 Red is hot and white is even hotter. 768 00:54:48,360 --> 00:54:53,400 These young bats are in a roost that is probably 20 degrees hotter 769 00:54:53,400 --> 00:54:54,840 than the rest of the cave, 770 00:54:54,840 --> 00:54:58,640 which means that they're able to grow at a phenomenal rate, 771 00:54:58,640 --> 00:55:00,520 making it the perfect incubator. 772 00:55:01,960 --> 00:55:05,120 The whole secret to this animal's success 773 00:55:05,120 --> 00:55:07,760 is the fact that it is part of a swarm. 774 00:55:07,760 --> 00:55:09,840 On their own, they wouldn't survive. 775 00:55:11,720 --> 00:55:15,360 Not only have the bats created a hostile environment 776 00:55:15,360 --> 00:55:17,520 that few others can survive in, 777 00:55:17,520 --> 00:55:19,680 their real genius is that, 778 00:55:19,680 --> 00:55:22,440 by filling it with millions of individuals, 779 00:55:22,440 --> 00:55:25,600 they've even managed to change conditions in the cave 780 00:55:25,600 --> 00:55:26,680 to suit the swarm. 781 00:55:27,800 --> 00:55:30,840 Well, this may be the perfect environment for rearing bats, 782 00:55:30,840 --> 00:55:34,720 but it's definitely not the perfect environment for humans. 783 00:55:34,720 --> 00:55:38,480 If I stay here much longer it could be fatal, so I'm off. 784 00:55:42,480 --> 00:55:46,280 By now, the bats have started their nightly exodus to feed. 785 00:55:54,320 --> 00:55:57,400 And for me, the only way back out of the cave is right through 786 00:55:57,400 --> 00:55:59,320 the eye of this gigantic bat swarm. 787 00:56:02,720 --> 00:56:06,760 There's literally tens, if not hundreds of thousands of them. 788 00:56:06,760 --> 00:56:10,640 I've never seen so many bats in one place in my life. 789 00:56:10,640 --> 00:56:15,440 This is the start of a ten million-strong swarm 790 00:56:15,440 --> 00:56:19,360 that will fly around and out of this cave for the next three hours. 791 00:56:28,200 --> 00:56:32,840 Surprisingly, these Mexican free-tailed bats are not very agile. 792 00:56:32,840 --> 00:56:35,480 They're not particularly manoeuvrable bats. 793 00:56:38,200 --> 00:56:40,400 Being tucked down in these caves 794 00:56:40,400 --> 00:56:44,120 means the bats have to commute long distances for food, 795 00:56:44,120 --> 00:56:46,880 so these are the speedy cross-country fliers 796 00:56:46,880 --> 00:56:48,000 of the bat world. 797 00:56:50,440 --> 00:56:53,880 Having to deal with some obstacles is a bit more of a challenge. 798 00:56:53,880 --> 00:56:55,720 Argh! Argh! 799 00:56:55,720 --> 00:56:58,520 Oh! Oh! 800 00:57:01,200 --> 00:57:03,080 This getting quite intense now. 801 00:57:03,080 --> 00:57:04,640 Argh! 802 00:57:04,640 --> 00:57:06,240 That was on my beard, that one. 803 00:57:10,600 --> 00:57:13,600 I'm being absolutely bombarded by bats. 804 00:57:17,880 --> 00:57:22,120 This would be some people's worst nightmare 805 00:57:22,120 --> 00:57:25,200 but, for me, to be inside in the eye of this swarm of bats 806 00:57:25,200 --> 00:57:27,600 is just the most thrilling experience. 807 00:57:36,640 --> 00:57:39,800 These bats are the ultimate opportunists. 808 00:57:39,800 --> 00:57:41,080 By swarming together, 809 00:57:41,080 --> 00:57:44,480 they're able to make their home where most others would fail... 810 00:57:47,000 --> 00:57:50,360 ..proving there are huge benefits to life in the swarm. 811 00:57:54,640 --> 00:57:56,520 Swarms are a way for animals 812 00:57:56,520 --> 00:57:59,280 to become significantly more successful. 813 00:58:00,520 --> 00:58:04,640 In working together, swarms become cleverer, stronger, 814 00:58:04,640 --> 00:58:07,720 and individuals are much more likely to survive. 815 00:58:10,640 --> 00:58:15,040 Understanding swarms is now also shedding light on how humans behave. 816 00:58:16,560 --> 00:58:20,840 With urban populations expected to double in the next 40 years... 817 00:58:21,840 --> 00:58:25,360 ..we're all going to have to get used to living amongst the crowd. 818 00:58:28,160 --> 00:58:32,160 Unlocking the secrets of the swarm could become critical.