From the Vault: Thirst, Part 3

What is thirst? In this Stuff to Blow Your Mind series, Robert and Joe dive into the biological, cultural and mythological answers to this broad question. (originally published 02/08/2022) 

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Episode Transcript

Speaker 1 (00:05):
Hey, you welcome to Stuff to Blow your Mind. My
name is Robert Lamb and I'm Joe McCormick, and it's Saturday.
Time to go into the vault for an older episode
of the show. This one originally aired on February eighth,
twenty twenty two. It's part three of our series about thirst.
Let's jump right in. Welcome to Stuff to Blow Your Mind,

(00:27):
a production of iHeartRadio. Hey, welcome to Stuff to Blow
your Mind. My name is Robert Lamb and I'm Joe McCormick,
and we're back with part three of our series on
the question of thirst. Now, if you remember, in the

(00:47):
last episode, Rob we talked about the biology of thirst,
anticipation of anticipation of the quenching of thirst. Because there's
this interesting thing where after you drink a glass of
water when you've been dehydrated, it takes some number of minutes,
maybe on the order of tens of minutes before that

(01:08):
water actually gets absorbed through the digestive system and ends
up in the blood and makes a difference systemically throughout
the body. And yet you still feel that that thirst
quinchiness after you have just the first glass of water.
You're not continuously chugging for ten to twenty minutes at
least hopefully not. But to start off today, I wanted

(01:29):
to come back to the question of how it is
that the body detects, the anticipates the coming changes in
your blood and your blood osmolality, which again is the
concentration of dissolved substances like mineral salts in your body's
water content, and how it anticipates those changes to provide

(01:53):
you that delicious feeling of having your thirst quenched by
a glass of water. Now, in the previous episodes, we
already talked about a few ways that the mouth in
the throat might detect the introduction of water into the
body and sort of sin signals to the brain saying hey, okay,
you can put the thirst on hold for now, there
are soon coming changes to the body's hydration levels. And

(02:17):
one of the ideas we talked about was the possibility
that temperature plays a role, because maybe there's some evidence
that the power of water to cool the mouth and
throat sends quinching signals to the brain. And also there
was some evidence that rodents were using sour taste receptors
in the mouth to detect the presence of water. But

(02:38):
Rob maybeing set me straight on this one. I don't
think it was clear that triggering the sour taste receptors
actually led to the quinching of thirst. Rather, it seemed
to encourage more drinking behavior when the mouse was thirsty.
Is that right? Yes, that's my understanding of these findings.
But I was actually reading about a few more studies

(02:59):
on exactly this question of how thirst quinching happens. What
is the mechanism that leads to these changes in the
brain that tell you, aha, thou art now quinched. So
the first thing I wanted to talk about was a
study that I was reading about a New York Times
article from twenty eighteen by Verny Greenwood called you get
thirsty and drink? How does your brain signal you've had enough?

(03:22):
And this is referring to a paper that I think
came up in passing in the previous episode, but it
was by Vinnie Augustine at all in Nature in twenty
eighteen called Hierarchical neural architecture underlying thirst regulation. And this
research has been looking at exactly this question we just
brought up, and they confirmed that, of course there is

(03:43):
a complex of neurons in the brain that appear to
cease activity after a thirsty mouse drinks water. So there
are some neurons that are apparently signaling that generating that
thirst motivation state. But then when a rodent takes some
water in through the mouth, those rons shut up, they
go quiet. So this would be the neural mechanism to

(04:04):
register quenching. But the question is what is the direct
mechanism that leads to the changes in those neurons. Now,
this New York Times article summarizes the findings as explained
by the first author on that paper, Vanite Augustine quote, Intriguingly,
what these cells are responding to is not the presence

(04:24):
of water itself, mister Augustine said. The researchers discovered that
letting a mouse take big gulps of water would spur
the neurons into action, but giving it water in gel form,
which had to be chewed before it could be swallowed,
did not. Neither did providing water in tiny two second
long SIPs, even when the animals consumed the same total

(04:48):
amount of water. In fact, giving the mice oil to
drink had just the same effect on the neurons as
gulping water. So that last part is a little gross,
but based on this fine name, uh, it would kind
of imply that a major mechanism leading these thirst neurons
to to say, okay, thirst has been quenched would have

(05:08):
something to do with like muscular movements in the throat,
the kind of gulping that you do when you're guzzling
down a bunch of water really fast. But technically maybe
it doesn't even have to be water, it's just any
fluid that you're gulping. I mean, as humans, we don't
I guess, drink a lot of just straight oil, but
we do drink a lot of things that are that
are to varying degrees removed from from from you know,

(05:31):
from from just a neutral water. So this would make sense, right,
But if you if you hydrate yourself in some other ways,
so like the examples that you say, consuming water in
gel form where you can't like gulp it down really
that still hydrates you, but that apparently does not lead
to this immediate quinching signal in the brain. Similarly, with

(05:53):
drinking water in very small isolated SIPs, I guess in
those cases you would eventually hydrate your self and your
thirst will eventually go away, but it will be more
likely that your body has to just become systemically hydrated
before the thirst goes away. It's not that sudden quinching
reward feeling. Now, there was an interesting detail offered here

(06:16):
about reasons that the body might need to have this
reaction where we turn off thirst very quickly after getting
a drink, like why not just wait for your blood
osmolality to reach the ideal level. Well, in previous episodes,
we talked about one reason for this, which is that
you know, if you actually did have to wait for
your body's water content to get all leveled out right

(06:38):
before your thirst went away, you might you might like
kill yourself drinking gallons and gallons of water because you
know over the course of the tens of minutes that
it takes for this change to take hold. But there's
another reason, one of the authors of this paper brings up.
That's in this Greenwood article in the Times quote. Aside
from the specter of water intoxication, there are good reasons

(06:59):
to drink only the minimum amount necessary when an animal
lowers its head to drink, doctor Oka speculated, and that's
doctor Yukioka. It's in quite a vulnerable position. Quote, if
you double the time of ingestion, that should double the
risk of being prey, he said, And I thought that
was interesting too. I mean, I think it is true

(07:20):
that in the natural environment, as we brought up in
the previous episode, going for water is often putting yourself
in a vulnerable position, you know, maybe exposing yourself from
hiding or shelter and sort of turning your attention away
from scanning your surroundings. Yeah. I mean in many cases too,
they the access point of the water might not provide

(07:42):
much in the way of cover for smaller animals, and
then for larger animals there may be you know, bodily
positions they have to get into to drink that put
them in a greater state of vulnerability. Like I'm thinking
of a draft for instance. Though draft, of course is
already formidable animal U but but still there's a certain

(08:05):
awkwardness present when it actually has to drink water. Sorry,
I just started thinking about game or fuel. Um, yeah,
this is this, says. I have no research to back
this up. They're just observational material for me. But I
think everyone knows that I enjoy watching the squirrels, and
we have a bird bath outside near our feeders, and

(08:29):
the bird bath is positioned right up against the fence,
and the squirrels drink from that all the time. But
I wonder how much I wonder how much of that
is that they're able to drink from the bird bath
while essentially remaining in a vertical position attached to the
to the fence, like they don't have to, you know,
go across a clearing. They have, I guess, pretty good

(08:52):
cover for a squirrel. Those squirrels are bold in other
ways that, you know, make you think that they're they're
less concerned, or they're or they're in control of the
situation as far as potential predators go. So if you
happen to have sitter squirrels and rover squirrels, your bird
bath is positioned in such a way that even the
sitter squirrels could could get to it. I guess so.

(09:13):
But then, yeah, I don't know. I'd be interested to
hear what anyone else out there has observed with their
squirrels and drinking water from bird baths and other water sources.
They seem to like one thing versus the other. I
don't know. They certainly drink more water than my cat.
I'll give them that well. Anyway, there was another article
from the very next year, also in the New York Times,

(09:34):
also by Greenwood, covering follow up research from some of
the same scientists. So this was published May thirty first,
twenty nineteen, just called the Neurobiology of Thirst, and this
is summarizing a study published in twenty nineteen in the
journal Neuron where the authors oh again the first author
on this one was Vanite Augustine and it was called

(09:56):
Temporally and spatially distinct thirst satiation Sig and the authors
here found that the pleasure we get from drinking when
thirsty is once again not directly related to hydration. It
is a reward pathway separated by both time and space
from the body's hydration and osmolality monitoring mechanisms. And one

(10:19):
of the major findings in this paper is that though
drinking water is associated with a dopamine release, this is
a typical signal that the brain is expecting a reward. Right.
You know, things that you want, you want to get
and feel good when you get them. That's often that
involves a dopamine release. But the feeling of reward in

(10:41):
the brain here is apparently not tied to becoming hydrated
after being dehydrated, but specifically to the act of drinking
water through the mouth. So if you're dehydrated and then
you suddenly receive water through an iv or even via
a direct injection into the stomach, your thirst will eventually
go away after your body adjusts to the new fluid levels,

(11:04):
but you won't get that feeling of reward satisfaction or
the corresponding dopamine release. Those come specifically from the activity
of drinking, the gulping of water through the mouth. And
picking up on this, I was actually looking at one
more paper that had an interesting finding. I wouldn't have
mentioned this. Other one was a little earlier. This was
from twenty sixteen published in Nature called thirst neurons anticipate

(11:28):
the homeostatic consequences of eating and drinking, And this is
by Zimmerman at All And this study found, among other things,
a dual track monitoring system for thirst management. So along
the lines we've already been talking about. It found that
if you take mice and you give them some salt
and make them thirsty, drinking water rapidly inhibits neurons in

(11:52):
a region of the brain called the subfornical organ or SFO,
and that leads to thirst quenching. And of course this
is before there's any notable change in blood osmolality. But
it also found that if you take these thirsty mice
and you give them very salty water and the opportunity
to drink it, they will drink it, and initially they

(12:14):
will gulp it down and it will inhibit the SFO
neurons and apparently quench thirst just like the freshwater. But
the quenching doesn't last for very long, and they write quote,
this initial decline was reversed after approximately one minute. This
indicates that the rapid anticipatory response to drinking has at
least two components, an immediate signal that tracks fluid ingestion

(12:38):
and a delayed signal that reports on fluid tonicity, possibly
generated by an esophageal or gastric osmo sensor. So if
you put all of this together, it seems like you've
got at least three different time dependent levels of sort
of the body's quinch watch. So you put them all together,
and you've got one system that's like, are you gulping fluid?

(13:01):
If you are, oh, that's very good, very good thou
art quinched, But then there's a second system on a
slight delay from that one, roughly one minute of delay
in mice. It's like, wait a second, what exactly was
that you were just gulping? Was that oil or was
that super salty water? You know, what are you trying
to pull? And if it well, if it was not

(13:23):
good fresh water, then it will cancel, cancel the quinch
and return the thirst. And then finally I guess there's
just the direct blood volume in osmolality monitoring, which is
on a much greater delay than the other two. So,
first of all, reminder, if anyone else, if anyone's interested
in the whole drinking saltwater thing, we did a whole
episode on drinking saltwater a while back. You should be

(13:46):
able to find that in the archives. Not a good
idea was it was one of the main findings there.
But the other thing, I think, and we've kind of
we've kind of touched on this a little bit already,
but you know, it would be in a steak to
think of like, Okay, it's just you know, what's drinking water,
water in water out, you know, even if you you
then acknowledge, okay, well, you know, the levels have to

(14:08):
be just right. But it's it's more than that. It's
not like organisms just one day we're like, hey, there's
water we can drink that we should use this to
our advantage. Now, like we are of water. So it's
like water in am water evolved out of things in water, etc.
So it's it makes sense that there would be a
more complex relationship with multiple triggers that you know that

(14:33):
we're still trying to understand. Yeah, I mean, as we
said at the very beginning, you you are the direct
descendant of creatures that long ago lived in the ocean
and all of your ancestors, just like you brought the
ocean with you onto land. The ocean is now inside
your skin. Yes. Oh, and before I wrap up, this
last study I mentioned also documents interesting evidence for the

(14:56):
the oral cooling mechanism of thirst quenching that I brought
up in previous episode. So the authors here say that quote.
We found that a playing cold but not room temperature
metal to the oral cavity of a wake thirsty mice
was sufficient to rapidly inhibit SFO neurons. Thus, temperature dependent

(15:17):
modulation of SFO neurons may explain the enigmatic connection between
oral cooling and thirst, including why thirsty rodents will avidly
lick cold metal, and humans report that sucking on ice
chips rapidly relieves thirst. That's interesting. I hadn't really thought
about that with sucking on ice chips though, though obviously,

(15:39):
I mean that's I think that's something we all do
if we have access to iced drinks. Of course, the
thing with ice, of course, is that ice melts in
your mouth as well and actually serves to hydrate you, right,
but that the cooling effect of having the ice in
the mouth may provide a level of thirst quenching sensation

(15:59):
that goes beyond the actual amount of water you're taking
in from that ice. This gives me a great idea, so,
showrunners and so forth, of the Witcher, if you're listening,
I would love to see a scene where Henry Cavill's
Witcher character share some wisdom and he's like, sometimes when
when I'm thirsty, I just have a good lick of

(16:19):
my sword takes care of you know. That'd be great,
And you haven't seen there was just kind of licking
is the blade of his sword. I'd never heard this
before that apparently thirsty, thirsty rodents will lick cold metal.
But yeah, I had not seen it. Yeah, but it's
good enough for mice, it's good enough for the witcher.
I think all Garrold's just gonna that's that's how you
cut your tongue, buddy, That's how you cut your tongue.

(16:42):
Oh you know. It reminds me of brom Stoker's Dracula.
We have that wonderful scene where Gary Oldman's elderly Dracula
licks the blood from the straight razor. See, he was
thirsty and he quenched the thirst. But also hopefully the
blade was cold enough that that also had an fact.
I well, I guess after all these studies we looked

(17:02):
at on the quenching mechanism, I'm wondering, so the two
main different ones have emerged. One is the oral cooling
mechanism and the other is the gulping mechanism. You know,
the muscular movements in the throat is you're swallowing large
amounts of water. And I guess I'm not sure if
these two different explanations are competing or if they're complementary.

(17:23):
Maybe they both play a role in regulating these thirst neurons.
In the SFO. I'm not sure. Now, given all the
things we've discussed about the complexity of thirst, sensations, and
water acquisition by various organisms, I thought it might be

(17:44):
interesting to look at a couple of examples that, in
different ways seem to hijack mechanisms of related to thirst
and our relationship with water, not only ours, but also
some other organisms for the benefit of a life form.
Not the life form that is that is potentially thirsty,

(18:05):
but a life form that is that is hijacking that organism,
such as a parasite or a virus. Oh. Interesting. So
the first one I want to mention here is is
one that definitely affects humans, and that is rabies. Now,
I imagine I think everyone has heard of rabies. If not,

(18:26):
buckle in because I'm gonna share a little bit. Though.
This is obviously a topic that you know, we could
really bust out if we wanted to and give a
full episode treatment. But even if you're just vaguely familiar
with rabies, uh, you know, you might not grasp the
full danger and horror of this particular zoonotic viral disease.
I think a while back, I've read at least somebody
making the case that rabies is a contender for like

(18:50):
the worst disease known. Yeah, it is pretty horrifying and
for a lot of people in um in the world,
particularly and let's let's say United States, you're lucky enough
to live largely removed from it. I think that the
US is sometimes class of classified as being free of

(19:11):
canine rabies. Now, there are still cases of canine rabies
that pop up, and there are deaths that occur, but
not at the same rate as other parts of the
world where the problem has not been contained as well.
So it's rabies is caused by the virus Lisa virus,
which essentially means rage poison. It's named for the Greek
goddess Lissa, the goddess of rage, fury and rabies, the

(19:37):
daughter of Nicks, sprung from the blood of Lauranus, and
she pops up in different tales, like for instance, at
the urging of Hera, she inflicts madness on Heracles, and
in some tellings she's also involved in the punishment of
the hunter Acteon, who's torn apart by his own mad
hunting dogs, and in memory Serves. There are some interesting

(19:59):
treatments of the this latter tale in art. Yeah, I
think he looked at a god or something to that effect.
You know, you don't have to do much to get
to torn apart by dogs when you're dealing with the
Greek pantheon. Yeah. I don't remember all the details, but
I think he makes Artemis angry for some reason, and
then he's a hunter. But then he's transformed into the quarry,

(20:22):
like he's transformed into a stag or something, and then
his own hunting dogs hunt atch. Right, there's some transformation
involved there as well. So humans have been exposed to
rabies for a very long time. It's um. It's thought
that it probably originated in old world bats and especially
flourished during the heyday of of dog domestication. So it is,

(20:43):
you know, it is. It is definitely tied to the
canine world. According to the History of Rabies in the
Western Hemisphere by Velasco Villa at All, published in Anti
Viral Research, the earliest record of a disease affecting humans
that's consistent with rabies and associated with dogs is found

(21:07):
in the Eshnuna cuneiform law tablets in ancient Mesopotamia dating
back to the eighteenth through nineteenth centuries BC. Wow, Yeah,
and I believe memories served it. It concerns like laws
concerning dogs biting people, like if you you have a
dog and it bites somebody. And of course we have
other references to either cases that seem like they could

(21:32):
be rabies, or we feel pretty strongly are referring to rabies.
Aristotle wrote seemed to have wrote of it in three
thirty BC. Quote dogs suffer from the madness. This causes
them to become very irritable, and all animals they bite
become diseased. Democratus and Hippocrates also wrote of it as well,

(21:52):
and there are comparisons to raging dogs in the Iliad
that it seems like maybe you're less certain that this
is referring, because of course a dog can rage. I
guess it doesn't have to be rabid. But there are
also mentions of the dog star Ryan exerting a malignant
influence on human health, and rabies is just a terrible disease,

(22:15):
especially when you really get into what it can do
to an organism and what it can do to a
human being. Today, it's vaccine preventable, and the vaccines keep improving,
but once clinical symptoms appear, it is one fatal According
to the World Health Organization, in ninety nine percent of cases,

(22:36):
domestic dogs are responsible for spreading it to humans. Again,
in the United States, it is effectively we're effectively canine
rabies free, though you will still find cases that occur
and deaths that occur, so it's it's still possible, but
it is largely under control. In other parts of the

(22:56):
world it's not the case. And so you know, this
is all great reminder why it is important to get
your dog a rabies vaccine and to also get yourself
immunized if you come into contact with the disease, right,
and that time is very important there, right, Yeah, so
that the incubation period for rabies is typically two to

(23:19):
three months, but may vary from one week to a year.
And I think it depends on like the viral load
and you know, being introduced into your body and some
other factors. And then there are two forms of the
disease that are possible in humans. So once you know
this virus is in your system, one version is paralytic rabies.

(23:39):
This only occurs in about twenty percent of cases, and
it consists of gradual muscle paralyzation, coma, and death. It's
often misdiagnosed, but again, like twenty percent of cases, this
is what occurs. The other, however, is the the the
incarnation of rabies that certainly brings to mind these ideas

(24:00):
of strange curses from the gods, you know, the really
horrible stuff, and that's furious rabies. Symptoms here include hyperactivity,
excitable behavior, hydrophobia, the fear of water, and sometimes aerophobia
as well, fear of drafts of fresh air or you know,
blasts of air, that sort of thing. And death occurs

(24:23):
in these cases within a few days due to cardiac arrest. Now,
I gotta admit I've always heard rabies described as or
associated with this idea of hydrophobia, which obviously, yeah, that
means fear of water, but I never knew exactly what
to make of that, Like what does that mean in practice? Yeah,

(24:44):
because it's you know, when you start thinking about like
the things that a viral infection does, like you know,
to what extent is it about prolonging that virus or
or or you know, achieving something, and it's um you know,
in its cycle, and as you look into it, it's
it's really quite interesting. So again, this is the really

(25:07):
horrible fate the furious rabies. If one comes down with
this person's behavior and mood is drastically altered, anxiety, hallucinations, confusion, paranoia, terror,
and they tend to experience both a profound thirst and
a severe inability to quench that thirst. So what does
all this mean? Well, keep in mind that saliva is

(25:29):
central to rabies transmission. You know, if you think of
you just hear the words rabid dog, the image that
probably comes to mind is that of a dog frothing
at the mouth, right, with frothing saliva right, And it's
generally understood that I guess the saliva is what transmits
the disease. Like if you are bitten by a dog

(25:50):
that has rabies or by an animal that has rabies,
the saliva will transmit it to your blood. Is that
a real route of transmission? Yes, that is the primary
route of transmission. Bites and scratches are are the most
common ways that it is just transmitted. There are other ways,
you know, basically any infected fluid could do it, but

(26:12):
those are uncommon compared to bites and scratches, especially when
you're you know, think of a dog, think of think
of even you know, a bat or any other organism
that would carry rabies. The bite is the thing, and
it's steered in these cases by you know, enhanced aggression
and altered behavior. And seemingly, you know, the mouth is
primed to transmit the virus by excess infectious frothing saliva. Okay,

(26:38):
so much in the same way that respiratory viruses that
are spread by aerosols or droplets might tend to cause
the infected person to cough or sneeze in order to
further spread themselves to other people. Uh, this disease that
is spread often by saliva into blood through bites, Uh,
it would tend to cause the infected animal to froth

(27:01):
in the mouth with a lot of infectious saliva and
to be irritable or or aggressive in ways that would
lead to biting. Right, And that brings us back to
this question of hydrophobia. Like, then then for what reason,
you know, seemingly, like what role does does the fear
and does this carror at the idea of water have
to do with anything? So in humans this peers to

(27:24):
manifest as a kind of panic that sets in when
presented with water and difficulty in or inability to drink,
like attempts to drink may result in spasms. There is
some clinical footage you can find online of individuals that
have been diagnosed with rabies attempting to drink water, and
I do not, I do not very disturbing footage, so

(27:46):
I don't recommend seeking it out. But if you find
yourself in need of of of the visuals for this, uh,
there there is some documentation online. I believe a case
in Vietnam is typically typically cited here. Now, does the
difficulty with drinking water when someone is infected with rabies

(28:08):
usually have something to do with difficulty in muscle control,
for like swallowing through neurological routes. Yes, yes, definitely so.
And the insidious nature of all this, though, is that
since the individual is prohibited from drinking water by the infection,
or at least the drinking water becomes excruciatingly difficult, saliva

(28:31):
production increases. You have hypersalivation, and they can't swallow the
excess saliva, and that's and they can't wash away this
excess frau thing saliva. So, in other words, it primes
the victim's mouth to be this potent transmitter of the virus,
especially through a bite. So it's um. Yeah, it has

(28:52):
a real insidious quality to it. But as as horrible
as rabies is. Again, fortunately there are vaccines that exist, right, yes,
So again all a great reminder get your pet vaccinated
for rabies. And if you come into contact with a
with an animal that has rabies or may have had rabies,
you definitely need to go to a doctor. They can

(29:14):
take care of it. You don't want this, this, this
is not an illness you want running its course. Yeah,
thank now. I wanted to share another example though that
seems to go or potentially goes in the opposite direction. Uh.
Rabies inhibits thirst and and and alters thirst in that direction.

(29:36):
But if we look to to to the world of
the horsehair worm, we see something that that may possibly
be involved in generating excessive thirst in the host. So uh,
this would have to do with parasitoid worms from the
phylum Nematomorphah. They're known as horsehair worms because they're threadlike

(30:01):
round worms that resemble the hair of a horse's tail
or maine. Now, some people may have seen these before.
These are creatures that you'll sometimes fine living free in
a puddle or stream. I think I saw one once
like this while while walking on my mom's property. But

(30:21):
you can also see them occasionally burst out of the
body of a cricket, mantis, beetle, or other host organism,
very much like a xenomorph. Oh, now, maybe I was
seeing something else, but I know I've seen video of
something that was like a long, thin worm that was
just gradually spooling out of a cricket sexoskeleton to just

(30:46):
and it just kept spooling and spooling and spooling, almost
like the clown car where you know, fifty clowns get
out of a Volkswagen. But it's a worm that seems
bigger than the cricket it was inside, yes, and it's
it's crazy to watch. I have a very vivid memory
of being in a junior high band environment and there
was a cricket on the floor and somebody in a

(31:08):
neighboring section was grossed out by the presence of the cricket,
and so they stopped it. And then once they had
stomped the cricket, this horsehair worm began emerging from the cricket,
which of course only further grows out the individual who'd
stopped the cricket. So there's kind of there's some sort
of weird, horrific justice in that. Like if you think
the crickets grows, will just wait till you see what

(31:29):
the encore is. Surely it helped that in band practice
that day you were playing Carmena barana. Yeah, if only so.
The interesting thing here is that the adults of this species,
in these these organisms, they are free living in the water,
but the larva are parasitic and grow to adulthood inside

(31:53):
the body of an insect. So I think you can
all imagine how this probably goes down. A male and
male horsehair worms mate and damp soil and fresh water,
and then the female lays millions of the eggs. These
eggs hatch and the tiny larvae insist on vegetation near
the water's edge. And then what happens while a cricket

(32:14):
or some other suitable host drops by, it ends up
eating that larva one way or another, either either the
you know, like a cricket is eating the grass, or
like a mantis is going to eat the larva itself.
And so what happens then is a like a cricket
comes along and it eats the grass that has this
larva on it, or if it's a carnivorous mantis, well

(32:38):
then it eats a cricket that has already been infected
by the larva. In either case, the larva winds up
inside of another organism, the cyst dissolves, and then the
juvenile worm escapes, bores through the gut wall, and starts
absorbing nutrients from the host organism. This worm has a

(32:58):
move fast and things philosophy. It is a It is
a disruptor of the internal organs of its host. Right,
And at this point, it's kind of it's kind of
like you can imagine it like a stowaway in the
hold of a ship. You know, it's it's rummaging around,
it's eating some of the stored food supplies, maybe eating
the occasional crew member on that ship and minute and

(33:22):
otherwise also damaging the ship. But it doesn't need If
you're a stowaway human stow and a ship, what do
you want to do? You want to get to a
port somewhere, right and uh, And likewise, with this worm,
it needs to get to water or damp soil in
order to continue its life cycle. Now, if if something
happens to the cricket. If it's gets stomped in on

(33:43):
the floor of a middle school band room, it's going
to escape. It's going to you know, abandoned ship, but
it needs to get to damp soil or fresh water.
So it may be moving fast and breaking things, but
it's going to try to do so in such a
way that it ends up at a certain place when
when the whole thing goes to put right, it needs

(34:04):
to steer the host in the right direction. And so
this is where we get that bit of parasitic hijacking
in action um or at least that's that's one hypothesis
of exactly what's going on. That the worm instills a
crazed thirst in the host so that it seeks out water.
That's sometimes referred to as the thirst hypothesis. An alternate

(34:25):
hypothesis states of the worm simply waits till the host
finds water on its own, and then it jumps out.
And it's my understanding that we're really not one hundred
percent sure what happens. That there's some some interesting evidence
for both both hypotheses. Ed Young and a twenty fourteen
Ted talk um mentioned that there's research that indicates that

(34:46):
this may occur because the organism releases proteins that alter
the crickets brain functionality. So and there does seem to
be some sort of of It seems like there is
a strong case to be made some sort of hijacking
is taking place, and if that's occurring, it may be
pushing the animal towards water via thirst. Okay, so I

(35:08):
guess that would mean you might be able to notice
this if you had a place where a bunch of
insects were getting infected by this parasite, they would be
showing a lot of drinking behavior, a lot of water
drinking behavior, right. But then again, yeah, there's also the
other argument. Well, it's just it's waiting until the water
is until it's drinking. Even even that, that would be

(35:28):
pretty impressive because it's that like, how does the how
does the worm know what's going on inside the darkness
of the cricket or the darkness of the mantis that
enables the stowaway to know that there is water or
damp soil close at hand. But I was looking at
some of the papers that discussed this, there was a
this is of course, this is a much older paper

(35:49):
now but there was a two thousand and one study
published in the German journal zoo Logisha and Zeiger that
says that the thirst hypothesis has been supported by observation
of quote unquote suicidal behavior by infected mantis is in
southern France that would seemingly jump into the water and
then immediately outcomes the worm. So that would be a

(36:11):
case where yeah, like the mantis is not just going
to the water, it is to drink and then it
bursts out. It's actually jumping in. It's it's it's giving
up the ghost. So but I guess with that you
still would have to ask your question, at what point
is there some hijacking of behavior. Was it the seeking
the water to begin with or was it something that

(36:32):
kicked in when the creature was close to water. So
we're not sure exactly you know which way way to
go on this as far as I understand based on
the research I was looking at. But it seems like
either way you're getting into these interesting Um you're getting
into the relationship between the host organism and water. You
know something about its uh it's bodily awareness of water

(36:56):
or the thirst or desire to be in close proximity
to water, and of course that is ultimately what the
parasite wants as well. Right, So the parasite either needs
a mechanism of making the host to go drink water
or knowing when the host is drinking water. Right. Oh,
in case anybody's worried, it's my understanding that occasionally humans

(37:18):
end up ingesting these things, But I don't think there's
ever been any evidence or anything to support the idea
that they're capable of hijacking human behavior. Again, if that
is indeed what's happening in the case of crickets and mantises, well,
what happens when humans do ingest them. It's just kind
of gross. They could like bombit them up. I was looking.
There were two Japanese cases reported in twenty twelve due

(37:41):
to the accidental ingestation of infected insects. I think in
these cases that this has occurred via the consumption of
vegetables that had those insisted larvae on them. You're in
it a Some vegetables seem like they'd be a lot
better at hiding a little stowaways than others. Oh yeah,
I have this consistent problem with broccoli. I love broccoli.

(38:02):
I love cooking with it. But I a number of
times I've been like giving it a rinse before I
cook it or something, and then I'm like, oh, there's
just a bug up in the up in the tree
limbs there. It's hiding out in a little fork in
the in the florets. That's true. I mean, I guess
the it's kind of a this kind of the thing
about broccoli, right, is that the thing that makes it

(38:23):
so delicious, that's it's so great to cook because you
get you know, all the oil or the seasoning, it
ends up just getting embedded there in all the little
mooks and crannies. It also means they are all these
additional places that I guess something could potentially hide, or
you could just end up with some dirt or grid
in there. Maybe I'm just getting my broccoli from really
buggy sources. I don't know. Sometimes I get like CSA broccoli,

(38:46):
that's it's it's really nice, good stuff, but there's just
like a there's just a big old bug in there,
just just like tarantulas crawling out of it through your
kitchen and stuff. Almost. I mean, it's all just a
good reminder, you know, wash your vegetables everybody, even if
you're not sure they need it. You know, you give
them a once over? Why not? Right, you'll feel better

(39:06):
about it, especially if you're if you're listening to this
episode whilst cooking. All right, we're gonna go ahead and
close out Thirst Part three. What do you think, Joe?
Do you think we'll be back with Thirst four colon
Thirst for Knowledge the Return of Jack Thirst. Yes, yes, yes,
we will be back. I'm sure of it. Yeah, like
this Thursday back this Thirst today back, Yes Thursday, this Thursday,

(39:31):
Thirst Part four, Thirst for More Knowledge, the final chapter
on the final chapter only on Stuff to Blow Your
Mind or some other topic. I don't know. We'll see
I guess all right. In the meantime, if you would
like to check out other episodes of Stuff to Blow
your Mind, you know where to find them. They're in
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and Thursday. You can find it wherever you get your podcasts.

(39:54):
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(40:15):
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(40:38):
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