You Have Never Been Stung by a Poisonous Jellyfish: Venom vs. Poison vs. Toxin

If I am going to blog about venom, I would be remiss to not write a “venom versus poison” post right from the get-go. The misuse of “venom” and “poison” is a pet peeve widely shared within the field of biology, let alone within the specialized field of toxinology. And yes, I said TOXINology, not toxicology. Toxinology is the study of the toxins, poisons, and venoms from plants, animals, and microbes; toxicology is the study of the effects of toxins, as well as other chemical substances, on living organisms.

Toxins are singular chemical substances that cause physiological harm to an organism. Put another way, a toxin is a single chemical that elicits a very specific kind of harm or bodily damage to a living creature. Here, I am also considering two addition criteria: 1) toxins must be capable of biological harm in small quantities (anything can be a toxin in large quantities) and 2) toxins are substances that occur in nature (artificial toxins are known as toxicants). Venoms and poisons are both complex mixtures of toxins, though within either of these chemical cocktails may be dominated by a specific toxin or toxin group.

The main difference between venom and poison is the method of delivery; venoms are actively delivered, whilst poisons are passively delivered. Venom requires a delivery mechanism, by way of fangs, spikes, pinchers, spurs, stinging cells (personal favorite) or some other devious method nature has conjured to cause a wound, transferring this venomous cocktail directly into the bloodstream or body cavity. Poisons are absorbed through the skin, ingested, or inhaled, thus these toxins enter the body by means of a natural opening to inflict direct internal damage. The passive nature of poison delivery is a reference to the lack of control a poisonous animal has to deliver its chemical mixture; the predator trying to eat (or the human unintentionally picking up) this animal has inflicted harm upon itself rather than the poisonous animal intentionally trying to cause harm. If you want to be fancy, there is a term for actively delivered posions: toxugens. Toxugen toxins fall into a gray area where they are not delivered via a wound, like a venom, but they are not passive means of defense, like most poisons.

So, in theory, you could drink venom. In fact, it has been done medicinally in the past. But I would certainly not recommend it. I would highly, highly, HIGHLY not recommend it.  Not only because it would likely cause a mad stomach ache, and the fact that any scratch or opening in your gastrointestinal track would be essentially inviting envenomation internally.

I would not recommend drinking venom because some components found in both venom and poison are actually the same toxin. You have heard that eating pufferfish is dangerous right? It is because these fish contain high amounts of tetrodotoxin (TTX), a potent neurotoxin that blocks the sodium ion pumps of nerve cells. No sodium pump, no action potential between your neurons, so no communication between your nerves and your muscles. That means no control of the muscles you need to breathe, leading to extreme respiratory paralysis. Death from respiratory failure can be 4-6 hours after consuming TTX.  You only need to ingest a few milligrams to kill an adult male. National Geographic estimates there is probably enough to kill 30 people in one fish, but it really depends on the concentration of TTX in individual pufferfish and the tolerance and/or body composition of the person ingesting TXX. Still, seems risky…

And TTX is not just found in pufferfish. If you have not done so before, I highly recommend googling blue-ringed octopus, the cephalopod genus Hapalochlaena. These adorable octopuses are some of the world’s most venomous creatures. These centimeter-long animals can easily kill a person in minutes with just one bite. What makes their venom so dangerous to humans? TTX.  Compared to the few milligrams you need to ingest, less than half a milligram of injected TTX is also lethal to an adult human male (the exact lethal amount of TTX for a human as either a poison or venom is not entirely clear, based on a review by the European Food safety authority).

Even more terrifying, TTX in the blue-ring octopus works whether this animal bites you or you bite it. Yes, this animal is both poisonous and venomous at the same time using the same chemical compound. According to Venoms: The Secrets of Nature’s Deadliest Weapon, a four-centimeter-long blue-ringed octopus could paralyze and drown a 240 lb sea turtle that accidently consumed it.

If you want to learn more about the chemistry of TTX and all the various animals that contain this potent toxin, check out this review from 2014.

So blue-ringed octopuses are both venomous and poisonous. Other animals, such as soil centipedes (Geophilomorph centipedes) and the Asian tiger keelback snake (Rhabdophis tigrinus) are also simultaneously venomous and poisonous. Each carries a venomous bite but also sequesters toxins from their diets into gland along their body. The slow loris could also be considered poisonous and venomous, since they produce poisons from glands in their elbows that they spread around their bodies but also mix this poison in their saliva for a “venomous” bite.

Venoms and poisons have a few other key differences, such as how they are made. Often poisons are produced exogenously, that is the toxins are actually acquired from the environment rather than synthesized within the animal. Take a poison dart frog out of its natural environment and give it a non-toxic diet, and it will lose its poisonous edge. However, there are some toads that do produce their own poisons as well. Venoms are almost always produced endogenously, which means toxins are produced within the animal. This means it is metabolically costly to produce venoms, so venomous animals play a dangerous game of balancing energy during their lifetime. You may have heard that snakes will sometime deliver a “dry” bite or that younger snakes are more dangerous than their elders. This relates to that tradeoff in metabolic energy in producing venom, referred to as the venom optimization hypothesis, or the behavior venom metering. Because venom costs metabolic energy, it behooves the venomous animal to be picky when to use it, since it would have to “pay” to produce more. It would also make sense to maintain some control over how much venom to use, thus saving yourself energy in the future on the chance of encountering a larger meal or needing for fight an angrier predator, or just making it to the next meal without starving. Younger animals may not have learned how to “meter” their venoms yet, meaning they do not have the instinct to dry bite as opposed to envenomate, making them more dangerous (though this is not a well validated idea).

Venoms are also utilized in multiple functions, beyond the typically defensive purpose of poisons. While often venoms are used to deter predators, their other main purpose is to capture prey. Spiders would not do so well evolutionarily without venom; their leggy and relatively soft bodies would have a hard time attacking and consuming the larger, more chitinous insects they prey upon without their chemical weaponry. Parasitic insects use venom for prey capture and prey manipulation: jewel wasps bite cockroaches first to paralyze the roach’s front legs and then bite a second time right into the brain to turn the roach into a zombie. These envenomated roaches meticulously clean themselves and allow the mother wasp to walk them roach a hole, lay an egg on top of its body, bury it, and the newly hatched larva to consume it, all while the roach is still alive. Why keep this animal alive? You know, to keep the food as fresh as possible. The western diamondback rattlesnake uses its venom to track down prey that it has bitten after it runs away. Assassin bugs use venom to digest meals from the inside out, liquefying the internal organs, while blood feeding animals like bats and ticks use their venom to stop blood from coagulating and analgesic components to keep their bites from being painful and their hosts from picking them off. Sea anemones use venoms in specialized stinging cells to fight with other anemones for space. Male platypus’s, and only males, use their venomous spurs during the mating season to fight off other competitors for a female.

So, let’s put it all together:

Toxin: biologically-derived chemical substance that causes physiological harm to an organism

Poison: either a singular toxin or mixture of toxins delivered passively, by means of absorption, inhalation, or ingestion, to another organism that causes illness, impairment, or other biological harm at a physiologically-dependent amount for the purpose of defense; often acquired exogenously

Venom: complex cocktail of toxins delivered through a specialized delivery mechanism from one organism to another for the purpose of predation, defense, digestion, competition, or other benefit of the organism delivering the venom; often acquired endogenously

And after that mouthful, a delightful visual summary of what this article is about.

29572267_584813261882468_6969849227810840584_nI don’t know who made this meme, but this article is dedicated to you.

I also hope you will check out these articles on Smithsonian.com and Discover (the latter by Venomous author and toxinologist Christie Wilcox) to learn even more about the difference between venoms,  poisons, and toxins.

Interested in testing you venomous versus poisonous skills? Science Friday featured a quiz on the very subject in February of this year.

References:

 

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