[♪ INTRO] If you’ve ever called snakes “poisonous”
around a herpetologist or, you know, that friend of yours, you know which one I mean,
there’s a good chance you’ll receive a lecture about the difference between venoms
and poisons. And it’s true that most snakes aren’t
considered poisonous. But nature loves an exception.
Meet the tiger keelback. They’ve got the best of both worlds: poison
for their predators and venom for their prey. It can be easy to confuse the terms venom and
poison, but the difference does actually matter. Both are made up of toxins, biological chemicals
that mess with body functions in small amounts. The technical difference has to do with how
they get into a victim’s body. Poisons enter passively, by being eaten, breathed
in, or absorbed through the skin. And because of that, they’re usually defensive,
an organism’s way of saying “Hey! Don’t touch me! You will regret that!” Venoms, on the other hand,
are actively injected into the body, like, via a pair of pointy
snake fangs, for example. Venom can certainly be used defensively, but
often, venomous animals are predators that use their toxins offensively, so they can enjoy
a meal without all that troublesome struggle. Since venoms and poisons tend to be used differently,
they usually contain different kinds of toxins. So a doctor would want to treat a snake poisoning
differently than a snake bite, or what’s known as envenoming. And the distinction is particularly important
if the snake in question is a tiger keelback. These snakes can be found across Southeastern
Asia, and they belong to a huge and diverse family of snakes called the Colubridae. These are sometimes referred to as “rear-fanged”
snakes because unlike rattlesnakes or cobras, which pump venom forcefully through hollow
fangs in the front of their mouths, colubrid fangs sit further back in the jaw
and deliver venom along open grooves. And they have to kind of chew on their prey
a bit to get the venom moving. Most of the time, tiger keelbacks use their
venom to take down tasty fish, tadpoles, and their favorite: frogs and toads. They rarely bite humans, but when they do,
it’s not a fantastic experience for the human. The venom can cause hemorrhaging and mess
with blood clotting, leading to excessive internal and external bleeding, and in several
known cases, death. Thankfully, antivenom is usually an effective
treatment, if delivered in time. Now, all this talk of killer
snake bites might sound scary, but it’s important to remember
that snakes don’t want to bite you! Really, they don’t! They’d much rather
save their venom for their prey. They don’t want to waste it on something
they can’t eat. And that may be partly why the tiger keelback
usually fends off threats another way. On the back of these snakes’ necks are several
pairs of nuchal glands. If the right pressure is applied, these glands crack
open and spew out a stinky, toxic yellow-ish pus. The poisonous nature of this stuff was first
noted in 1935, when a scientist who was dissecting a keelback cut into its nuchal glands, accidentally
spraying the poison right into his eye! Which is just one of the many stories that
science teachers have heard, and why they get so fussy about
you wearing your safety goggles. The poison contains bufadienolides, which
can cause acute pain and temporary damage to the cornea if they get in your eyes. When ingested or inhaled, they can irritate any
tissue they touch and even cause heart problems. And the snakes know how to use their poison. When confronted with danger, they assume an
arched posture and aim their neck towards the threat. Sometimes, they’ll even swing their neck
at an attacker, poison glands first, in a maneuver that scientists have delightfully
named a “neck butt.” Maybe the most interesting thing about this
poison is that they don’t make it. They pick it up from the toads they eat. Research has shown that tiger keelbacks living
on toad-free islands don’t have these poisons, but they can become
poisonous if given toxic toads. And you’d think that a lack of poison would
be a problem for a newborn snake, but it turns out mama keelbacks
can pass toxins along to their young. It’s unclear if she adds it to the yolks
or just bathes her eggs in the stuff. Experiments have shown that keelback babies
absorb toxins through their eggshells. Either way, by the time baby keelbacks hatch,
they’re ready to defend themselves. And here’s something super weird: the snakes
are more likely to flee from threats than face them neck-on if they’ve
been deprived of toads, suggesting the animals somehow
know when they’re poisonous. Also, the snakes don’t just take the toad
toxins as-is and stick them in their glands, they actually modify them chemically to make
them even more potent. The tiger keelback is definitely the
best-known example of a poisonous snake, but it’s likely not the only one. Other related species have nuchal glands,
so they might have poisons of their own that
simply haven’t been studied. Research has found that other snakes, like
garter snakes, can eat so much poisonous prey their organs become toxic to predators. Since most people don’t usually eat snakes,
there could be a number of species that would make us sick that we just don’t know about. So future studies may reveal that the tiger
keelback isn’t that much of an exception after all. In the meantime, you can tell that pedantic friend
of yours that there definitely are poisonous snakes. So Mleh! Thanks for watching this episode of SciShow! And a special thank you especially to our
patrons on Patreon. We wouldn’t be able to have all this fun
making awesome educational science videos like this if it weren’t for the support
of our patron community. If you’d like to learn more about joining
that community, or how you can help us do what we do, you can head on over to Patreon.com/SciShow [♪ OUTRO]
Venom helps kill prey and deter predators/clumsy players, poison can only be used to take an opponent down after you've died. Either way toxins are expensive so I'd wager venom with some dry bites thrown in is the best method rather than always on poison you gather from something else and having to give up stealth stats. Or I guess both, no need to attack if they see you're poisonous.
Both venom and poison...Why?