WEBVTT - Can Parasitic Worms Control Snails' Minds? 0:00:01.840 --> 0:00:07.520 Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff 0:00:07.600 --> 0:00:12.480 Lauren Vogel bomb here. By one estimate, somewhere around forty 0:00:12.480 --> 0:00:16.960 percent of all known animal species are parasitic, from tapeworms 0:00:17.000 --> 0:00:19.560 that grow in fish up to thirty feet that's nine 0:00:19.600 --> 0:00:22.599 meters in length, to a cough drop sized crustacean that 0:00:22.720 --> 0:00:26.160 drinks shrimp blood to survive. A planet Earth is crawling 0:00:26.280 --> 0:00:29.880 with parasites. Many of them have evolved to find very 0:00:29.880 --> 0:00:33.400 specific hosts. A take a louse that happens to be 0:00:33.479 --> 0:00:37.400 named s Gary Larsnai the after cartoonist Gary Larsen, who 0:00:37.440 --> 0:00:41.040 created The Far Side. This louse spends its entire life 0:00:41.040 --> 0:00:44.280 cycle on the skin of an unsuspecting owl, where the 0:00:44.400 --> 0:00:48.840 stowaway feeds on feathers and other organic materials. No other 0:00:48.880 --> 0:00:51.600 animals are known to harbor this particular kind of louse. 0:00:53.120 --> 0:00:57.480 But sometimes one host isn't enough. Sometimes the only way 0:00:57.520 --> 0:01:00.360 for a parasite to reproduce and complete its own life 0:01:00.360 --> 0:01:05.000 cycle is by passing through multiple carriers. Such is the 0:01:05.040 --> 0:01:07.959 case of the banded brood sec, which is a genus 0:01:07.959 --> 0:01:11.160 of worm by the name of Leucochloridium that's been accused 0:01:11.160 --> 0:01:15.720 of turning snails into zombies. This behavior is said to 0:01:15.720 --> 0:01:19.200 be part of an elaborate scheme that also involves hungry 0:01:19.240 --> 0:01:23.360 birds and their poop. Supposedly, if things go according to plan, 0:01:23.680 --> 0:01:26.800 the worm's plan, that is, those poor snails get their 0:01:26.800 --> 0:01:31.639 eyes pecked out and banded brood secks aren't just weird, 0:01:32.080 --> 0:01:37.880 they're flukes. Literally. Flukes, also known as trematodes, are flatworms 0:01:37.920 --> 0:01:41.520 that use suckers to grab hold of various objects. There 0:01:41.560 --> 0:01:46.120 are around eighteen to twenty four thousand different species. All 0:01:46.160 --> 0:01:49.880 of them are parasitic, and most have complex life cycles 0:01:49.880 --> 0:01:54.040 that depend on different host species at different times. Usually, 0:01:54.120 --> 0:01:56.800 the parasites spend at least part of their lives investing 0:01:56.880 --> 0:01:59.920 some kind of mollusk, that is, the spineless animal group 0:02:00.000 --> 0:02:05.920 whose membership includes octopuses, muscles, and yes, snails. Depending on 0:02:05.960 --> 0:02:09.400 the species, a fluke might shack up inside the host's kidneys, 0:02:09.480 --> 0:02:13.480 digestive structures, or even as reproductive organs. As snails are 0:02:13.520 --> 0:02:18.000 a common target for trematodes, and without them, the zombifying 0:02:18.080 --> 0:02:23.640 banded brood sacks simply couldn't procreate as adults. They are 0:02:23.760 --> 0:02:28.200 long flat worms that infest bug eating birds. Their specific 0:02:28.200 --> 0:02:31.040 habitat of choice is the bird's cloaca, which is the 0:02:31.040 --> 0:02:34.720 orifice through which birds both poop and reproduce. Don't bother 0:02:34.800 --> 0:02:39.080 judging them before it dies, A grown banded broodsack may 0:02:39.120 --> 0:02:42.680 spend weeks or months living inside its avian host. The 0:02:42.840 --> 0:02:46.880 timeline isn't quite clear. At some point, though, the parasites 0:02:47.000 --> 0:02:50.280 lay their eggs, which get pooped out by the bird 0:02:51.120 --> 0:02:53.280 and you know what eats a lot of bird droppings, 0:02:53.680 --> 0:02:57.480 ground dwelling snails. If the right kind of snail happens 0:02:57.520 --> 0:03:00.400 to gorge itself on feces laced with the flukeat eggs, 0:03:00.600 --> 0:03:05.400 things get a little bit surreal. After a target snail 0:03:05.480 --> 0:03:09.560 gobbles the eggs up, they'll hatch into clear bodied newborns. 0:03:10.440 --> 0:03:13.560 In the next phase of their development, the sphoresist stage, 0:03:13.960 --> 0:03:17.920 the little guys may develop their titular brood sacks. These 0:03:17.960 --> 0:03:22.400 sacks are pulsating, colorfully banded tubes that are jam packed 0:03:22.440 --> 0:03:27.040 with larvae, and they look sort of like wiggly little caterpillars. 0:03:27.880 --> 0:03:32.320 Maybe they're supposed to. The thing about these brood sacks 0:03:32.360 --> 0:03:35.120 is they don't pop up just anywhere on the snail's body. 0:03:36.040 --> 0:03:39.440 The snails view the world through light sensitive eye spots. 0:03:39.920 --> 0:03:42.160 Each one is located on the tip of a tentacle 0:03:42.320 --> 0:03:46.400 or eyestalk connected to these snail's head. A healthy snail 0:03:46.440 --> 0:03:48.880 can withdraw its tentacles and pull them back into its 0:03:48.920 --> 0:03:51.880 head whenever it likes. You may have noticed this yourself 0:03:51.880 --> 0:03:55.560 if you've ever picked one up. But when a snail 0:03:55.600 --> 0:03:59.320 gets infected with these flatworms, the eye stalks become hampered. 0:04:00.080 --> 0:04:03.920 The fluke's swelling brood sacks invade the tentacles, which prevents 0:04:03.960 --> 0:04:09.160 the snail from retracting them. Then, adding insult to inconvenience, 0:04:09.560 --> 0:04:13.680 the sacks start to pulsate. They expand and contract in 0:04:13.720 --> 0:04:17.000 a sort of dance. They can pulsate dozens of times 0:04:17.040 --> 0:04:21.240 per minute, and their color schemes are eye catching bands 0:04:21.279 --> 0:04:25.360 and speckles in shades of green, orange, yellow, white, black, 0:04:25.480 --> 0:04:29.320 or brown. Thanks to the snail's ultra thin skin, the 0:04:29.480 --> 0:04:32.240 entire show is clearly visible and sort of like an 0:04:32.360 --> 0:04:37.839 extremely slow rave. There could be an evolutionary method to 0:04:37.920 --> 0:04:42.760 this madness, though since the early eighteen hundreds, naturalists have 0:04:42.839 --> 0:04:46.240 wondered if this performance is just a ploy designed to 0:04:46.360 --> 0:04:50.560 trick birds into mistaking these brood sacks for juicy little caterpillars. 0:04:51.320 --> 0:04:53.440 Any bird that plucked one off of a snail would 0:04:53.440 --> 0:04:55.960 get a mouthful of larvae ready to make a beeline 0:04:56.000 --> 0:04:58.800 for its Cloaca grow up into adult flukes and begin 0:04:58.839 --> 0:05:04.720 the cycle anew. But okay, we mentioned zombies. Here's where 0:05:04.720 --> 0:05:08.640 that comes in. During the nineteen twenties and thirties, a 0:05:08.680 --> 0:05:12.640 few scientists proposed that banded brood sacks actively manipulate the 0:05:12.640 --> 0:05:17.440 way that snails behave. The parasites allegedly force their hosts 0:05:17.480 --> 0:05:21.560 to deviate from their normal routine. Influenced by the flukes, 0:05:21.800 --> 0:05:25.479 the hapless snails are driven into exposed and well lit 0:05:25.520 --> 0:05:29.480 areas like leaftops, high up off the ground. Once they're 0:05:29.520 --> 0:05:33.000 in the open, the snails make easy targets. The caterpillar 0:05:33.040 --> 0:05:36.680 loving birds see the dancing sphoresists and hungrily rip them 0:05:36.720 --> 0:05:41.600 out along with the ice talks. Or so goes the hypothesis. 0:05:42.640 --> 0:05:45.320 The trouble is field researchers have never seen this happen 0:05:45.360 --> 0:05:50.360 in the wild. Experiments conducted in eighteen seventy four did 0:05:50.400 --> 0:05:53.880 find that captive birds were more than happy to attack 0:05:53.920 --> 0:05:58.080 the throbbing sporocysts of infected snails, But that doesn't prove 0:05:58.200 --> 0:06:01.560 that the same thing occurs in nature. Some animals have 0:06:01.640 --> 0:06:04.200 been known to change their habits in captivity. After all, 0:06:05.880 --> 0:06:09.400 research is actually ongoing. But when all said and done, 0:06:09.560 --> 0:06:12.400 there's still a lot we don't know about the relationship 0:06:12.400 --> 0:06:16.520 between the flukes and their hosts. If these parasites really 0:06:16.560 --> 0:06:19.960 do influence the snails, which seems likely, how the heck 0:06:20.000 --> 0:06:23.440 do they do it? And do the brood secks really 0:06:23.520 --> 0:06:27.240 fool wild birds into thinking that they're caterpillars? If not, 0:06:27.520 --> 0:06:30.000 then how to adult flukes find their way into a 0:06:30.040 --> 0:06:36.080 feathered host's kloeca. Maybe we'll have clear answers someday. In 0:06:36.120 --> 0:06:44.520 the meantime, we certainly have some nightmare fuel. Today's episode 0:06:44.600 --> 0:06:47.560 is based on the article do these nightmare parasites hack 0:06:47.680 --> 0:06:50.599 snail brains to survive? On how stuffworks dot Com? Written 0:06:50.600 --> 0:06:53.280 by Mark Nancini. Brain Stuff is production of by Heart 0:06:53.400 --> 0:06:55.720 Radio in partnership with how stuffworks dot Com and is 0:06:55.760 --> 0:06:59.080 produced by Tyler Klang. Four more podcasts my Heart Radio, 0:06:59.279 --> 0:07:01.880 visit the iheartrak a you ap Apple Podcasts, or wherever 0:07:01.960 --> 0:07:03.360 you listen to your favorite shows.