Why Do Warm Climates Have More Poisonous Animals than Cold Climates?
July 3, 2004 10:49 AM   Subscribe

Why do warm climates seem to have more poisonous animals than cold ones?
posted by gimonca to Science & Nature (8 answers total)
At a guess, I'd say it's because most of the commonly-known poisonous/venomous animals are reptiles, which are exothermic, and as such, generally require warm temperatures to survive.
posted by biscotti at 10:55 AM on July 3, 2004

But then there are spiders. Yet the nasty ones of these are also in the warmer places.

However the cool climates have their problems. Mosquitos and biting flies mar the peace in poison-free places like northern Michigan.

As for snakes, there are plenty non-poisonous ones in places without the poison ones. Even plenty of pit vipers (rattlers, cotton mouths, copperheads etc) in places that freeze in winter. The nastier ones like coral snakes, cobras and taipans (neurotoxic) are in warm climates.
posted by Goofyy at 11:47 AM on July 3, 2004

Not a biologist, only an amateur, but I haven't heard anything correlating venom/poison/toxins with warmer climates.

There's more stuff in the tropics. A hectare of Costa Rican rain forest will have more species than ten million hectares of Canadian tundra, or something along those lines. So you've got a larger sample to draw upon: Canada ends up with fewer poisonous plant species, but a whole whopping shitload of poison ivy, for example. So it's a question of biodiversity: 80 per cent of snake species, for example, are non-venomous; there's just a lot more species in the tropics, and you don't hear about the obscure little harmless slug-eating tree snakes that are neither deadly nor boa constrictors.

Ironically for your hypothesis, venom helps snakes in colder climates. Snakes require warm temperatures to digest their food. Venom, in addition to subduing prey that would be otherwise dangerous to take out, begins to digest it before it's swallowed. Fun! But it means that timber rattlesnakes, for example, digest their food better at colder temperatures than they otherwise would. (Snakes actually do better in cold temperatures than any other reptile, because they're all core and no extremities.)

The big invertebrates are found in the tropics; though size and toxicity don't seem to be correlated, I'd still feel better encountering a one-inch centipede than its foot-long monster tropical holy shit that's big cousin . . .
posted by mcwetboy at 11:52 AM on July 3, 2004

Another WAG, but it may also have something to do with an animal's energy budget. In cold regions, you need to dedicate more energy to just staying warm. An animal in a cold climate that's maintaining venom sacs is taking that away from what may be more immediate needs, making it less fit from a natural-selection standpoint.
posted by adamrice at 12:00 PM on July 3, 2004

I think it's just out of a sense of fairness. We get the dark and the cold, those born in permanent good weather should suffer somehow.

Or what mcwetboy said. A place like Canada doesn't generally have the wide variety of species here, especially in bugs, that you see in the tropics.
posted by Salmonberry at 12:55 PM on July 3, 2004

yeah, I was gonna throw in the "there's just more of everything there" hypothesis, too. Of course, that's true for the rain forest, but probably not for the desert... or anyway, less true for the desert. So does the desert have more poisonous species than an average northern forest? I have no idea. I guess in northern forests, you're more worried about large, strong mammals than about small, poisonous snakes, on average... perhaps that's just supporting biscotti's answer, that snakes, reptiles, insects might be poisonous, but mammals generally aren't (though they may carry diseases), and the species native to the different climates tend to break down that way too.
posted by mdn at 1:08 PM on July 3, 2004

It's interesting that it doesn't matter whether or not there actually *are* more poisonous animals in warm climates than cold climates, but that the perception exists that there are. I don't have any idea whether that's true. Let's see.

Contrary to mcwetboy, I think that size and toxicity are related, though not in an absolute way. I know that baby copperheads are more poisonous than adults. And are there any poisonous anythings bigger than a cat? Poison exists as a defense mechanism primarily among small animals, or as part of a predatory strategy among other small animals. Larger animals rely on their physical size or speed for predation and escape.

Now up to a point, large animals are better adapted to surviving in cold climates than small animals due to issues of body mass and heat retention. It follows then that if poison is a trait of small animals, and small animals aren't well adapted to cold environments, then there are fewer poisonous animals in cold climates by virtue of the fact that there are fewer small animals.
posted by Jeff Howard at 4:15 PM on July 3, 2004

"If it don't stick, stink or sting, it ain't from Texas."
posted by jfuller at 8:23 PM on July 3, 2004

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