This episode is brought to you by the Music for Scientists album,
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Theft in nature isn’t exactly a novel idea.
I mean, animals steal stuff from each other all the time.
Squirrels steal food. Burrowing owls steal burrows.
Emperor penguins will even take each other's chicks.
But some of nature’s most extreme thieves might be the toxin-stealers.
Taking another creature’s poison is a little harder than just nabbing a nut or a nest.
To do it without hurting yourself, you need serious biological tricks.
But thanks to some clever adaptations,
animals have managed to steal all kinds of toxins — including these five.
First up are pore-forming toxins.
These are mostly produced by certain bacteria,
but they’re also used by cnidarians,
a group that includes sea anemones and jellyfish.
If you’ve ever been stung by a jellyfish,
you’ve experienced a dose of pore-forming toxin.
As the name implies, these toxins form pores in cell membranes,
making the membrane permeable.
In other words, the toxin puts holes in the target cells,
which can cause them to rupture. And when that happens,
the cell loses critical nutrients.
Even worse, those pores also give other toxins a way in.
So, even if the pores themselves don’t cause a cell to die,
some other substance might.
What’s weird, though, is that despite being super dangerous,
cnidarian toxins are also found in certain kinds of worm-like species,
including nudibranchs, flatworms, and at least one true worm.
And these worms don’t produce the toxins themselves:
They take them from cnidarians and use them for their own defense.
Take aeolid nudibranchs, for example.
Commonly called sea slugs, these animals are some of the few that can
successfully wrangle a stinging cnidarian, like a coral or an anemone.
After they catch their prey, the nudibranchs eat the animal's tentacles,
including the nematocysts, the part that delivers the venom.
Somehow, they do this without getting stung themselves.
But that’s still not the most impressive part.
Once the slug has ingested the nematocysts,
they travel through its digestive system to special glands in its cerata,
which are short, tentacle-like structures on the outside of the slug's body.
Then, when it's threatened, the slug can deliver its venomous payload
by detaching the cerata.
And this might be a sort of multi-purpose defense mechanism:
The detached cerata could sting the predator,
but could also just distract it while the slug makes its escape.
Next up, we’ve got cyanogenic glucosides,
which are toxins produced by plants for self-defense.
Chewing or digesting a cyanogenic glucoside releases hydrogen cyanide,
a compound just as deadly in real life as it is in the movies.
Hydrogen cyanide deprives cells of oxygen, and that can ultimately cause cell death.
Except, these glucosides are also found in some plants
that are regularly eaten by herbivores.
So in many cases, like for the birds-foot trefoil, these compounds don’t protect them
from large animals. Like, cows can pretty happily munch on this stuff.
But the glucosides do provide protection against
smaller predators like snails and insects.
That is, except for the six-spot burnet,
a moth that depends on birds-foot trefoil as a larval host.
Like cows, the burnet’s larvae can eat trefoil all day without suffering ill effects,
despite being much, much smaller than our bovine friends.
And to pull this off, the larvae have a few tricks.
For one, they eat fast, which limits the amount of time
they’re in contact with the cyanogenic glucosides.
But most importantly, the environment in their gut
just doesn’t break down those compounds.
In an acidic gut like ours, those molecules would be digested and release
hydrogen cyanide, but the burnet larva has a gut that’s more basic than acidic.
The burnet isn’t the only member of the moth and butterfly family
that doesn’t digest these molecules, but what happens next is the special part.
See, the burnet larvae don’t just leave the glucosides alone.
Instead, they move them into their own tissues.
Scientists don’t know much about how they do this, but they know that
once the glucosides are in place, they act as a powerful defense mechanism.
In fact, the intact molecules remain in the insect’s tissues
even after it turns into a moth.
The moth keeps the glucosides in “defense droplets” inside cavities in its skin.
And then, when the moth tangles with a predator, it releases the droplets.
In small doses, this means the moth tastes bad.
But in large doses, it might be deadly.
Most predators never find out, though,
because they know better than to bother a six-spot burnet.
Up next are the cardenolides.
These are cardiac-active steroids, which broadly means they mess with the heart.
Once inside your body, they block the sodium-potassium pump,
a structure responsible for transporting those elements across cell membranes.
Blocking them can cause an irregular heartbeat, and if it’s severe enough,
can lead to heart blockage or even cardiac arrest.
Cardenolides are found in plants all over the world,
including the African Acokanthera tree, which has a cardenolide called
ouabain in its bark and roots.
Indigenous Somalis use this toxin to poison their arrow tips
and make it easier to bring down big game like elephants.
And the usefulness of ouabain hasn’t been lost on the African crested rat, either.
It deliberately steals the tree’s toxin by chewing its roots and bark,
mixing it up with its saliva.
Then, the creature applies this mixture to the specialized guard hairs that cover its
body, kind of like how you might slather on a conditioner or a styling gel.
The guard hairs absorb the toxin and then deliver it
to any predator that’s foolish enough to bite the rat.
What’s especially wild is that cardenolides are the same toxins used in rat poison,
yet they don’t seem to harm this particular rodent.
Scientists don’t really know why, but it might be because their salivary glands are
unusually large and may produce secretions that can somehow process the toxin.
Now, like cardenolides, bufadienolides are steroidal toxins.
And they also affect sodium-potassium pumps.
They cause an increase in sodium and a decrease in potassium in the cell,
which prevents the cell from conducting electricity.
That can lead to a heartbeat that’s too fast or too slow.
And again, in severe cases, it can cause cardiac arrest.
But don’t tell that to the tiger keelback.
This snake keeps bufadienolides in special glands on its neck called nuchal glands.
But again, it doesn’t make these toxins itself.
This time, it gets them from the toads that it eats.
Luckily for the snake, it’s resistant to bufadienolides.
In fact, a lot of snakes have a natural resistance to these toxins,
including ones that don’t even eat toads.
Studies have found that these snakes seem to get their immunity
from unique amino acids on the part of the pump that binds to the toxin.
But the tiger keelback goes beyond mere protection:
It puts the toxin to work for its own defense.
When a predator damages the snake’s nuchal gland tissue,
it gets rewarded with a mouthful of stinky, yellow toxin.
As for how the toxin gets there, a 2007 study found that
the tiger keelback’s nuchal glands are full of tiny blood vessels called capillaries,
suggesting that the toxins are transported there in blood plasma.
And when the snake doesn’t eat toads,
it also doesn’t have bufadienolides in its glands at all.
Instead, they fill up with really benign stuff, like water, lipids, and carbohydrates.
So toad-eating isn’t just about food: It’s also important for self-defense.
And as a nice bonus, mother snakes can pass the toxin
along to their offspring, as well.
And finally, batrachotoxins are poisons that affect the nervous system.
These toxins affect the sodium channels in nerves and muscles,
changing their sensitivity to voltage and their ability
to choose which ions to transfer across membranes.
The result is that nerves that can no longer send signals to muscles,
which is pretty bad news, especially for the heart.
Humans famously steal batrachotoxins from poison dart frogs,
so-named because the toxin can be used to make darts a whole lot more lethal.
But other animals steal these toxins, too, though not necessarily from frogs.
New Guinean passerine birds get batrachotoxins
from the melyrid beetles that they eat.
Like poison-dart frogs, the birds aren’t affected by the toxins, possibly because they
have special sodium channels that have evolved resistance to them.
Regardless, somewhere along the evolutionary road,
the birds developed the ability to store these toxins
and secrete them in their feathers and skin.
Instead of, you know, just digesting them.
Scientists aren’t completely sure how they do this, but the result is clear:
The birds themselves become toxic.
See, feathers in general act as a barrier between a predator and a bird’s flesh.
For most birds, it isn’t a super effective barrier
because the predator can just pluck out the feathers.
But if you’re a passerine, predators that mess with your feathers
will get a nasty surprise.
The toxin dose isn’t usually large enough to kill,
but it can cause respiratory irritation and other unpleasantries.
The toxin also seems to help the passerine ward off parasites, like lice.
In fact, a 1999 study found that lice seem to deliberately avoid
the feathers of toxic birds.
Lice that do come into contact with the toxin also had shorter lifespans.
So, fewer lice to start with, and a shorter irritation from those that do attach!
Some studies also suggest that the passerine may be able to transfer batrachotoxins
from their feathers to their eggs, potentially protecting the eggs from nest robbers.
So, whether it’s something they do deliberately,
or bit of a happy accident, nature’s thieves can be pretty crafty!
Also, toxin-stealing is still an active area of research,
so it’s probably a lot more common than scientists even realize.
Still, there’s a lot to appreciate about what we do understand.
How these animals sequester and use toxins can teach us important things
about how structures in their bodies evolved and how species interact.
Just, you know, make sure you handle with care.
If all of these toxin-stealing animals have got you pumped up about
the wonders of the world, you might want to check out Music for Scientists after this.
It’s an album that was inspired by the beauty of science.
The songs were written and recorded by Patrick Olsen,
and the whole project is an homage to people of science.
If you want to check it out, we recommend starting with Aristarchus in the Rain,
which is a bit of a bop.
You can start streaming at the link in the description.
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