1 00:00:01,840 --> 00:00:07,520 Speaker 1: Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff 2 00:00:07,600 --> 00:00:12,480 Speaker 1: Lauren Vogel bomb here. By one estimate, somewhere around forty 3 00:00:12,480 --> 00:00:16,960 Speaker 1: percent of all known animal species are parasitic, from tapeworms 4 00:00:17,000 --> 00:00:19,560 Speaker 1: that grow in fish up to thirty feet that's nine 5 00:00:19,600 --> 00:00:22,599 Speaker 1: meters in length, to a cough drop sized crustacean that 6 00:00:22,720 --> 00:00:26,160 Speaker 1: drinks shrimp blood to survive. A planet Earth is crawling 7 00:00:26,280 --> 00:00:29,880 Speaker 1: with parasites. Many of them have evolved to find very 8 00:00:29,880 --> 00:00:33,400 Speaker 1: specific hosts. A take a louse that happens to be 9 00:00:33,479 --> 00:00:37,400 Speaker 1: named s Gary Larsnai the after cartoonist Gary Larsen, who 10 00:00:37,440 --> 00:00:41,040 Speaker 1: created The Far Side. This louse spends its entire life 11 00:00:41,040 --> 00:00:44,280 Speaker 1: cycle on the skin of an unsuspecting owl, where the 12 00:00:44,400 --> 00:00:48,840 Speaker 1: stowaway feeds on feathers and other organic materials. No other 13 00:00:48,880 --> 00:00:51,600 Speaker 1: animals are known to harbor this particular kind of louse. 14 00:00:53,120 --> 00:00:57,480 Speaker 1: But sometimes one host isn't enough. Sometimes the only way 15 00:00:57,520 --> 00:01:00,360 Speaker 1: for a parasite to reproduce and complete its own life 16 00:01:00,360 --> 00:01:05,000 Speaker 1: cycle is by passing through multiple carriers. Such is the 17 00:01:05,040 --> 00:01:07,959 Speaker 1: case of the banded brood sec, which is a genus 18 00:01:07,959 --> 00:01:11,160 Speaker 1: of worm by the name of Leucochloridium that's been accused 19 00:01:11,160 --> 00:01:15,720 Speaker 1: of turning snails into zombies. This behavior is said to 20 00:01:15,720 --> 00:01:19,200 Speaker 1: be part of an elaborate scheme that also involves hungry 21 00:01:19,240 --> 00:01:23,360 Speaker 1: birds and their poop. Supposedly, if things go according to plan, 22 00:01:23,680 --> 00:01:26,800 Speaker 1: the worm's plan, that is, those poor snails get their 23 00:01:26,800 --> 00:01:31,639 Speaker 1: eyes pecked out and banded brood secks aren't just weird, 24 00:01:32,080 --> 00:01:37,880 Speaker 1: they're flukes. Literally. Flukes, also known as trematodes, are flatworms 25 00:01:37,920 --> 00:01:41,520 Speaker 1: that use suckers to grab hold of various objects. There 26 00:01:41,560 --> 00:01:46,120 Speaker 1: are around eighteen to twenty four thousand different species. All 27 00:01:46,160 --> 00:01:49,880 Speaker 1: of them are parasitic, and most have complex life cycles 28 00:01:49,880 --> 00:01:54,040 Speaker 1: that depend on different host species at different times. Usually, 29 00:01:54,120 --> 00:01:56,800 Speaker 1: the parasites spend at least part of their lives investing 30 00:01:56,880 --> 00:01:59,920 Speaker 1: some kind of mollusk, that is, the spineless animal group 31 00:02:00,000 --> 00:02:05,920 Speaker 1: whose membership includes octopuses, muscles, and yes, snails. Depending on 32 00:02:05,960 --> 00:02:09,400 Speaker 1: the species, a fluke might shack up inside the host's kidneys, 33 00:02:09,480 --> 00:02:13,480 Speaker 1: digestive structures, or even as reproductive organs. As snails are 34 00:02:13,520 --> 00:02:18,000 Speaker 1: a common target for trematodes, and without them, the zombifying 35 00:02:18,080 --> 00:02:23,640 Speaker 1: banded brood sacks simply couldn't procreate as adults. They are 36 00:02:23,760 --> 00:02:28,200 Speaker 1: long flat worms that infest bug eating birds. Their specific 37 00:02:28,200 --> 00:02:31,040 Speaker 1: habitat of choice is the bird's cloaca, which is the 38 00:02:31,040 --> 00:02:34,720 Speaker 1: orifice through which birds both poop and reproduce. Don't bother 39 00:02:34,800 --> 00:02:39,080 Speaker 1: judging them before it dies, A grown banded broodsack may 40 00:02:39,120 --> 00:02:42,680 Speaker 1: spend weeks or months living inside its avian host. The 41 00:02:42,840 --> 00:02:46,880 Speaker 1: timeline isn't quite clear. At some point, though, the parasites 42 00:02:47,000 --> 00:02:50,280 Speaker 1: lay their eggs, which get pooped out by the bird 43 00:02:51,120 --> 00:02:53,280 Speaker 1: and you know what eats a lot of bird droppings, 44 00:02:53,680 --> 00:02:57,480 Speaker 1: ground dwelling snails. If the right kind of snail happens 45 00:02:57,520 --> 00:03:00,400 Speaker 1: to gorge itself on feces laced with the flukeat eggs, 46 00:03:00,600 --> 00:03:05,400 Speaker 1: things get a little bit surreal. After a target snail 47 00:03:05,480 --> 00:03:09,560 Speaker 1: gobbles the eggs up, they'll hatch into clear bodied newborns. 48 00:03:10,440 --> 00:03:13,560 Speaker 1: In the next phase of their development, the sphoresist stage, 49 00:03:13,960 --> 00:03:17,920 Speaker 1: the little guys may develop their titular brood sacks. These 50 00:03:17,960 --> 00:03:22,400 Speaker 1: sacks are pulsating, colorfully banded tubes that are jam packed 51 00:03:22,440 --> 00:03:27,040 Speaker 1: with larvae, and they look sort of like wiggly little caterpillars. 52 00:03:27,880 --> 00:03:32,320 Speaker 1: Maybe they're supposed to. The thing about these brood sacks 53 00:03:32,360 --> 00:03:35,120 Speaker 1: is they don't pop up just anywhere on the snail's body. 54 00:03:36,040 --> 00:03:39,440 Speaker 1: The snails view the world through light sensitive eye spots. 55 00:03:39,920 --> 00:03:42,160 Speaker 1: Each one is located on the tip of a tentacle 56 00:03:42,320 --> 00:03:46,400 Speaker 1: or eyestalk connected to these snail's head. A healthy snail 57 00:03:46,440 --> 00:03:48,880 Speaker 1: can withdraw its tentacles and pull them back into its 58 00:03:48,920 --> 00:03:51,880 Speaker 1: head whenever it likes. You may have noticed this yourself 59 00:03:51,880 --> 00:03:55,560 Speaker 1: if you've ever picked one up. But when a snail 60 00:03:55,600 --> 00:03:59,320 Speaker 1: gets infected with these flatworms, the eye stalks become hampered. 61 00:04:00,080 --> 00:04:03,920 Speaker 1: The fluke's swelling brood sacks invade the tentacles, which prevents 62 00:04:03,960 --> 00:04:09,160 Speaker 1: the snail from retracting them. Then, adding insult to inconvenience, 63 00:04:09,560 --> 00:04:13,680 Speaker 1: the sacks start to pulsate. They expand and contract in 64 00:04:13,720 --> 00:04:17,000 Speaker 1: a sort of dance. They can pulsate dozens of times 65 00:04:17,040 --> 00:04:21,240 Speaker 1: per minute, and their color schemes are eye catching bands 66 00:04:21,279 --> 00:04:25,360 Speaker 1: and speckles in shades of green, orange, yellow, white, black, 67 00:04:25,480 --> 00:04:29,320 Speaker 1: or brown. Thanks to the snail's ultra thin skin, the 68 00:04:29,480 --> 00:04:32,240 Speaker 1: entire show is clearly visible and sort of like an 69 00:04:32,360 --> 00:04:37,839 Speaker 1: extremely slow rave. There could be an evolutionary method to 70 00:04:37,920 --> 00:04:42,760 Speaker 1: this madness, though since the early eighteen hundreds, naturalists have 71 00:04:42,839 --> 00:04:46,240 Speaker 1: wondered if this performance is just a ploy designed to 72 00:04:46,360 --> 00:04:50,560 Speaker 1: trick birds into mistaking these brood sacks for juicy little caterpillars. 73 00:04:51,320 --> 00:04:53,440 Speaker 1: Any bird that plucked one off of a snail would 74 00:04:53,440 --> 00:04:55,960 Speaker 1: get a mouthful of larvae ready to make a beeline 75 00:04:56,000 --> 00:04:58,800 Speaker 1: for its Cloaca grow up into adult flukes and begin 76 00:04:58,839 --> 00:05:04,720 Speaker 1: the cycle anew. But okay, we mentioned zombies. Here's where 77 00:05:04,720 --> 00:05:08,640 Speaker 1: that comes in. During the nineteen twenties and thirties, a 78 00:05:08,680 --> 00:05:12,640 Speaker 1: few scientists proposed that banded brood sacks actively manipulate the 79 00:05:12,640 --> 00:05:17,440 Speaker 1: way that snails behave. The parasites allegedly force their hosts 80 00:05:17,480 --> 00:05:21,560 Speaker 1: to deviate from their normal routine. Influenced by the flukes, 81 00:05:21,800 --> 00:05:25,479 Speaker 1: the hapless snails are driven into exposed and well lit 82 00:05:25,520 --> 00:05:29,480 Speaker 1: areas like leaftops, high up off the ground. Once they're 83 00:05:29,520 --> 00:05:33,000 Speaker 1: in the open, the snails make easy targets. The caterpillar 84 00:05:33,040 --> 00:05:36,680 Speaker 1: loving birds see the dancing sphoresists and hungrily rip them 85 00:05:36,720 --> 00:05:41,600 Speaker 1: out along with the ice talks. Or so goes the hypothesis. 86 00:05:42,640 --> 00:05:45,320 Speaker 1: The trouble is field researchers have never seen this happen 87 00:05:45,360 --> 00:05:50,360 Speaker 1: in the wild. Experiments conducted in eighteen seventy four did 88 00:05:50,400 --> 00:05:53,880 Speaker 1: find that captive birds were more than happy to attack 89 00:05:53,920 --> 00:05:58,080 Speaker 1: the throbbing sporocysts of infected snails, But that doesn't prove 90 00:05:58,200 --> 00:06:01,560 Speaker 1: that the same thing occurs in nature. Some animals have 91 00:06:01,640 --> 00:06:04,200 Speaker 1: been known to change their habits in captivity. After all, 92 00:06:05,880 --> 00:06:09,400 Speaker 1: research is actually ongoing. But when all said and done, 93 00:06:09,560 --> 00:06:12,400 Speaker 1: there's still a lot we don't know about the relationship 94 00:06:12,400 --> 00:06:16,520 Speaker 1: between the flukes and their hosts. If these parasites really 95 00:06:16,560 --> 00:06:19,960 Speaker 1: do influence the snails, which seems likely, how the heck 96 00:06:20,000 --> 00:06:23,440 Speaker 1: do they do it? And do the brood secks really 97 00:06:23,520 --> 00:06:27,240 Speaker 1: fool wild birds into thinking that they're caterpillars? If not, 98 00:06:27,520 --> 00:06:30,000 Speaker 1: then how to adult flukes find their way into a 99 00:06:30,040 --> 00:06:36,080 Speaker 1: feathered host's kloeca. Maybe we'll have clear answers someday. In 100 00:06:36,120 --> 00:06:44,520 Speaker 1: the meantime, we certainly have some nightmare fuel. Today's episode 101 00:06:44,600 --> 00:06:47,560 Speaker 1: is based on the article do these nightmare parasites hack 102 00:06:47,680 --> 00:06:50,599 Speaker 1: snail brains to survive? On how stuffworks dot Com? Written 103 00:06:50,600 --> 00:06:53,280 Speaker 1: by Mark Nancini. Brain Stuff is production of by Heart 104 00:06:53,400 --> 00:06:55,720 Speaker 1: Radio in partnership with how stuffworks dot Com and is 105 00:06:55,760 --> 00:06:59,080 Speaker 1: produced by Tyler Klang. Four more podcasts my Heart Radio, 106 00:06:59,279 --> 00:07:01,880 Speaker 1: visit the iheartrak a you ap Apple Podcasts, or wherever 107 00:07:01,960 --> 00:07:03,360 Speaker 1: you listen to your favorite shows.