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Some animals are so deadly just a drop of venom can kill a full grown adult in minutes. But how did these animals get so deadly? Which animals are the most venomous? Join SciShow for a fun and spooky episode all about our poisonous friends!

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References for this episode can be found in the Google document here:

Thanks again to Dr. Bryan Fry at the University of Queensland.



There are a lot of ways to kill and be killed in the animal kingdom, but only a lucky few use the powers of venom. This toxic tribe includes species of snakes, spiders, scorpions, snails, jellyfish, bees, and even a few weirdo mammals. Clearly not all these animals are closely related, so how did they acquire these same defenses? Where did venom come from and how does it work? Also, you're curious, I bet, just what animals can kill you the quickest. But do you really wanna know? Really?

[intro music]

Just like birds, bats, and bees all have wings but are found in very different places on the tree of life, so too are our venomous friends a good example of convergent evolution, where diverse animals evolve similar features separately at different points in time.


 Evolution of venoms and toxins

Member of the Cnidarian phylum, like anemones and sea jellies, are by far the oldest venomous creatures, from five hundred to seven hundred million years old. Scorpions and centipedes have been around for at least four hundred million years, making them the oldest venomous land lineage, and venomous snakes share a common ancestor with venomous lizards like the Gila monster and the komodo dragon, whose toxic ways go back some two hundred million years.

Venoms didn't just come out of nowhere. They all evolved through the mutation of protein genes. Some venoms are closely related to digestive enzymes, like those found in saliva, while others are more similar to immune system proteins designed to fight off invading bacteria. Although there are loads of different venoms in all sorts of crazy animals, they seem to mostly all into two broad categories: those that attack neuron receptors, and those that mess with the blood's ability to clot. These are the two best ways to chemically kill something quickly, which is why all venoms are similar, whether you're an octopus or an ant.

Yes, there are venomous octopuses.

 â€‹Venom vs. poison

Venom is technically different than poison. Poison must be ingested, inhaled, or absorbed, whereas venom is always injected via fangs, spines, beaks, tales or tentacles. Venomous creatures brew their own toxins, while some poisonous creatures acquire them from the environment, which is something I'll get back to in a minute.

 â€‹So who's the biggest baddest most deadly toxic avenger of the animal kingdom?

Now it's time to discuss who the biggest baddest most deadly toxic avenger of the animal kingdom is. Well, the answer is that we really can't say for sure. There are just too many variables in species behavior and physiology and environment to say authoritatively who is the deadliest of them all. But we do know that certain animals have acquired the most devastating combination of toxic potency and quantity of poison delivered in a single strike.


 Australian box jelly fish

The Australian box jelly fish, for example, is no doubt one of the most venomous creatures on Earth. This ancient bad Larry has a body the size of a beach ball that trails about sixty thin three meter long tentacles, each equipped with millions of nematocysts, harpoon-like mechanisms that spring on contact, injecting venom into its victims. Those little things are a pretty amazing adaptation. After all, if you're a gelatinous blob lacking both tooth and claw you can't just blob your prey to death and risk your own fragile jelly body. You have to totally immobilize it before it can struggle. And the venom the box jellies carry is one of the most powerful concoctions known: a cocktail of neurotoxins which mess with the nervous system, cardiotoxins which try to shut down your heart, and dermonecrotic chemicals that kill living flesh. Just rotten zombie flesh.

When a swimming human is unfortunate enough to be stung by one of these blobs, the venom can cause respiratory failure and cardiac arrest, two things you don't want to have happen to you. In fact, the stings are so intensely and immediately painful that victims often go into shock and drown before they even ever reach shore.


 Cone snails

And while you're avoiding beach balls that you're not familiar with at the beach, don't be picking up pretty shells willy nilly either. Cone snails, found in warm waters all over the world, have extraordinarily long venom glands, like tiny transparent harpoons that can pierce a wetsuit and inject you with the world's fastest acting venom. Which you may not actually even feel because it also contains a painkiller.

Most venomous creatures produce one or just a few toxins, but the cone snail has up to one hundred different toxins in its arsenal, each designed to target different parts of the nervous system. For example, tests on lab mice have shown that one component causes tremors in mice while another puts them to sleep. It's possible that cone snails can produce so many different types of toxins because they duplicate their genes faster than any known organism in the animal kingdom. This fast and continuous turnover of their venom genes basically throws their defense mechanisms into evolutionary overdrive.


 Venomous snakes

So now you're thinking to yourself: oh, I'll just avoid the ocean completely, and I'll be safe, right? Well, think again. Over one hundred thousand people world wide die each year due to bites from one of the more than six hundred species of venomous snakes on Earth.

Snakes prove that having the most powerful toxin doesn't always make you the most dangerous. For example, banded sea kraits, found in tropical Indo-Pacific waters, have incredibly potent venom, but they're shy and docile and not likely to attack humans. Whereas puff adders, vipers found throughout sub-Saharan Africa, have weaker venom but are more aggressive and have killed lots and lots and lots of humans. 

King cobras, found in South-East Asia, are the world's longest venomous snake, reaching lengths up to nearly six meters -terrifying!- and can unleash enough venom in a single bit to bring down an adult elephant in a few hours. Why? Why do you have so much venom? What are you gonna do with an elephant?

And yet the king cobra's venom pales in comparison to that of the Australian inland taipan. Largely recognized as the most venomous snake on the planet, their venom is loaded with taipoxin, the most lethal known serpentine neurotoxin, along with a dash of protease enzymes that help digest proteins, and procoagulants, which interfere with blood clotting. But while the inland taipan's venom is record-breaking it's a shy snake, and nearly all recorded bite victims have been pushy herpetologists who were really kind of asking for it. Relax, they have the anti-venom.


 Golden dart frog

While the next creature is technically poisonous and not venomous, it's also amazingly potent, so we had to include it. Meet the golden dart frog, found in the Amazonian rainforest. These five centimeter psychedelically colored frogs secrete the most powerful animal toxin in the world, an extraordinarily poisonous alkaloid called batrachotoxin. It's at least twenty times more deadly than any other poison frog species' poison and about two hundred and fifty times more potent than strychnine.

Alkaloids are complex bitter organic bases, typically found in certain seed plants. Morphine, nicotine, and caffeine are all types of alkaloids that distinctly affect humans who consume them. Now batrachotoxin is an insanely potent neuro- and cardiotoxin, which means it sucker punches you in your brain and in your heart, which are both very important to being alive, quickly stopping the transmission of nerve impulses, and leading to near immediate paralysis of vital muscles, like the heart.

The frogs use their poison solely for defense against hungry birds, but indigenous tribes long ago learned how to exploit this deadly resource by dipping their arrows in the poison. Hence the name, dart frog. A drop of this juice is so potent that a dipped dart can remain deadly for two years. *whispers* Two years.

Now what's especially interesting with dart frog's poison is that it comes from the animal's diet. Wild frogs eat a specific diet of beetles, termites, and especially alkaloid-rich ants, which make them poisonous. The same frogs in captivity are typically fed fruit flies, and their toxicity drops over time, losing their mojo like Popeye eating iceberg lettuce.


 Brazilian wandering spider

And how could I talk about toxic animals without mentioning a spider? Well, beat their venomous king: the hairy hand-sized Brazilian wandering spider. Called 'wandering' for its tendency to rove around at night, during the day these guys like hide under logs and in clusters of bananas. They're on a perpetual walkabout and not just in Brazil. In 2005 one turned up in England when it crawled out of a fruit bowl full of imported bananas and bit some poor chap right there in his kitchen. He was fine. After a week in the hospital.

Unlike many spiders these guys are pretty aggressive and use modified fore limbs that act as fangs to inject their venom into anyone who honks them off or looks good to eat. The neurotoxin PHTX3 is one component of their venom. It overstimulates serotonin receptor sites on nerves throughout the body, causing intense pain. Meanwhile the juice gets to work on paralyzing your muscles, which can be especially problematic when your diaphragm freezes up, leading to asphyxiation. Luckily there is an anti-venom - if you can find a dose quick enough.

If excruciating pain and the threat of death weren't enough, this spider's venom has another bizarre side-effect. For men it triggers the release of nitric oxide which can cause priapism. That is a intense involuntary and painful erection that can last for hours. Yep. And the odd silver living to this is of course that scientists are now studying the way that that works in hopes with coming up with alternatives to Viagra.


 Silver linings

The fact is these natural poisons aren't all bad. Lots of medical research is being done today to explore the potential healing powers of venom. New studies are looking at snake venom to treat arthritis, scorpion venom to fight brain cancer, and the golden dart frog's alkaloid toxins for use as a pain stronger than morphine. Just goes to show that German renaissance alchemist Paracelsus had it right when he famously said: "There are no poisons, only poisonous doses."

And that, folks, is how you take lemons, and make lemonade.



Special thanks to doctor Fry at the University of Queensland for his help with this episode, and thanks for watching this episode of SciShow. If you have any questions, comments, or suggestions you can always find us on Facebook and Twitter or of course down in the comments below. And if you wanna keep getting smarter with us here at SciShow you can go to and subscribe.