[WARNING! SPIDERS IN THE VIDEO ] Why are the most venomous species found in the warmest places on Earth? I mean, take Australia for example. Depending on who you ask, it has all or nearly all of the ten most venomous snakes in the world, plus the funnel-Web spider, the blue ringed octopus, box jellyfish, paralysis tick and stonefish, all found in Australia, are the most lethal of their kind and even this cute platypus has an ankle spur, which in the male, secretes a venom that can kill a dog. In humans it would merely cause excruciating pain. This question, why do the most venomous species live in the warmest places, is one that I've wondered about for most of my life. Perhaps it's because I was born here in the small town of Traralgon, Australia. This is the first house where I ever lived. As my mum recalls {Derek's Mum}"in the backyard there was a shade where we found red backs, and I used to play in the shed? {Derek's Mum}"I don't think once we found the red backs that we let you in there.". Yeah, that's very comforting. Thanks mum. Now if you don't know what a red back is, it's a very poisonous spider. Hold up. I gotta tell past Derek something. You see it's important that we say venomous and not poisonous because poisonous means it'll be harmful if you eat it, whereas venomous means it'll try to eat you and that will be harmful. Continue. So thankfully they never bit me, otherwise, I wouldn't be standing here today. Now before we go any further, it's probably worth asking, is it true, do more venomous species really live in hot places? Well apparently I'm not the only one who thinks so because I found this reddit thread on the topic. Though, it really didn't explain why that was the case. But what about the data? Well, here is a map of the global average temperatures. Compare that with this map that I've colored in according to the number of venomous species in each country. The country with the most venomous species is Mexico with eighty different organisms with the power to kill you. That's followed closely by Brazil and then Australia. Well this seems to all match up very well with the global average temperatures. So why is it so? My first hypothesis was that there's something about the heat which enables the formation of these venom molecules. So I ran that idea past Professor Polyakov of Periodic Videos {Professor Polyakov}"no intent filter" [alright] "because the reason is that if you go up a ten degrees centigrade change in temperature round about room temperature [okay], will only double the rate of most chemical reactions and I don't think anything evolutionary is likely to evolve to such a big difference based on just a factor of two in the rates." So maybe it's worth asking what are these venom molecules exactly? Well, in most species where the venom is delivered by fangs it is evolved from saliva. In the funnel-web spider for example, the lethal effect seems quite accidental. What you've got to understand about venom, it's there, it's a secondary thing that it actually kills. The actual reason that spiders have got venom is to digest their prey. That they happen to do most of it before they actually eat it. Injecting the venom and the venom will start to liquefy whatever they've caught and, once it's turned to liquid, all spiders live on soup. The funnel-web evolved without any humans or other primates around and yet, ironically, its venom is most potent for exactly this group. Biggest evolutionary joke ever, the only group of animals with backbones that's actually allergic to their venom are the primates. We don't have primates in Australia. All right, so it's lemurs, monkeys, apes and us. Thus most species deliver, not just one type of venom molecule but a whole cocktail of different proteins that range in length from short chain to very long chain molecules and these molecules can serve a range of functions. Some are neurotoxins which can disable your nervous system. Others are hemotoxins which actually attack your blood cells and can dissolve tissues, but since we're talking about cocktails, what would happen if you drank some venom? You could take a vial of taipan venom and happily have it with your scotch and it wouldn't be a problem as long as you didn't have any irritation on the mucosal lining or any stomach ulcer or things like this. It's got to get into the bloodstream to be a problem. Okay, so since drinking the venom is not gonna kill you, what should you do if you get bitten by say an inland taipan? That's the world's most venomous land snake. What you do? Don't panic. Stay calm. I think that would be easier said than done. The venom travels through the lymphatic system, so it doesn't usually travel through the veins or the blood vessels, so that's just quite close on under the skin, and if it reaches your nervous system it'll shut down the signaling pathways that keep your heart beating and your lungs breathing, and so what actually kills you is suffocation. So what you need to do is stay very still and bandage up the limb that's been bitten from the tip all the way back to your torso. Now the bandage needs to be really tight to trap the venom within the lymphatic system, but not so tight as to cut off the blood flow to the limb. Now once you've got it bandaged up, you need to find some anti-venom. What is anti-venom? Well, it's made by injecting a large organism like a horse with a dilute solution of the venom. The horse then produces antibodies for that venom which you can harvest and inject into yourself in case you get bitten. Making anti-venom is tough work. It would take seventy milkings of a funnel-web spider to get enough venom to make a single dose of anti-venom and what's worse anti-venom can only be used on an individual a limited number of times because over those uses your body will build up antibodies to the anti-venom making the anti-venom ineffective. So you might wonder well, why can't you just inject yourself with dilute amounts of venom and build up your own antibodies to the venom? That would work except for the fact that when you get bitten you need to have a lot of antibodies in your system and to keep your antibodies at that high level you would need to keep injecting yourself with the venom, say every month and that's probably not the best thing for you. But why is it that people in warm climates need to worry about this and not people in cold climates? Well, I went to the experts to find out about this trend. You know broadly, yeah, there's really not much of a pattern happening. Really? What about that reddit thread and the map I made? If you're saying, is there a global pattern showing that you get more venomous animals in hot places, I don't know if there is. In snakes, which is the group that I'm most familiar with, in Australia the pattern is the diametric reverse of that one. If you wander around Southern Australia, every snake you find on that Kosciusko is venomous. If you wander around the tropics of Darwin, you're very unlikely to see a venomous snake. They're all pythons and harmless colubrid snakes. Now this is unexpected. The most venomous snakes in Australia live in the coldest places and the reason for that is? 20 million years ago an itinerant sea snake coming down from Asia as Australia drifted up to Asia, got to Australia. It was venomous to start with. There were no snakes in Australia at the time and so venomous snakes radiated through Australia. This big family called the elapid II the Cobra family. Okay, but on a global scale, my point remains. There are more venomous species in hot countries. There's gonna be vastly more venomous snakes in a warm climate area than in a cold climate area. The problem is that there's vastly more snakes. So as a proportion of the snakes that are there, the venomous guys are probably going to be about the same and maybe even less in the case of a place like Australia than they would be in a cold area. So why are there more venomous species in warm places? Well the truth is there aren't, at least not as a proportion of species. The majority of venomous species on Earth are ectotherms. Those are organisms whose body temperatures are regulated by their surroundings. Now that means that they can only really have short bursts of energy, so instead of chasing down prey and running away from predators, they needed a different strategy to allow them to survive and so many of them evolved venom. There is a greater diversity of ectotherms in warm climates, so it only stands to reason that there will be a greater number of venomous species. But that's not to say that there aren't venomous species in cold places. The only snakes that get into the arctic circle are European vipers, a venomous species. But biodiversity alone isn't the complete answer to this question. It also depends on evolutionary history. If you had come to Australia 20 million years ago, there would have been no snakes at all. The venomous ones got here first and the non-venomous came after. I think it's a really lousy explanation, but it's the best one that we've got. Why is that a lousy explanation? Well it's doesn't invite any lovely complicated piece of ecological theory or anything else. It's just relying on history. But this is a pattern that's very strong and doesn't seem to be explicable any other way and nowadays in Hawaii there are no venomous snakes and the same goes for Jamaica. These are warm places that just haven't evolved or have lost any venomous snakes that they may have had. So it might just be a lucky accident that we've been fortunate enough to be blessed with a few venomous spiders. I am also reminded that we're living in a particular point in time, roughly 15,000 years after the last ice age. Now that would have wiped a lot of the ectotherms from the Northern Latitudes of the Northern Hemisphere. For example, in Ireland there are no snakes because the place was wiped clean by an ice sheet and snakes haven't managed to get back to the island yet. My point is the distribution of species depends on what happened. It may be an unsatisfying explanation, but I'd rather know the truth than just believe in a trend that's not actually there. Really? [you're] a decimal What do you think is gonna happen to the spot on the screen as I narrow... The color of the blue morpho is created by the structure of its scales Which is what you do - butterflies? But see all your organs [are] where the signs are getting lost - wings makes mathletes [a] trap the light and if you should not flare out Would never realize with the size learns and certainty [prints] directed alert so... As I started to go through this big investigation, I realize just how complicated this is and how many mysteries are still out there. For example, why are some species deadly venomous and in others the venom is is pretty weak, and I didn't end up with anything. The deadly guys turned out to have ecologies that are very similar to the guys with very weak venom and it may be a historical accident. Another strange observation is that a lot of snakes that have evolved more recently have actually lost the ability to produce venom. The big success story in snakes worldwide are the harmless ones. They've actually evolved from venomous snakes Venom is an ancestral characteristic in modern snakes. The successful snakes are the ones that left it behind and they gave it up and they're proliferated despite not having venom, Apparently the cost of making venom isn't much more than the cost of making saliva. So it seems curious that they would lose what seems to be a killer advantage over other species. If you have thoughts about this or any other mysteries regarding the global distribution of venomous species put them in the comments below.
Not any more!
So primates never evolved in the direction of spider resistance?