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  • [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.

[WARNING! SPIDERS IN THE VIDEO ]

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