A Great Lakes bush viper

Most venomous reptiles use their teeth to deliver their toxins. Vipers, like this Great Lakes bush viper (Atheris nitshcei) administer theirs through hollow, retractable teeth. © reptiles4all/ Shutterstock

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Bite or be bitten: What is the difference between poison and venom?

Venom and poison can both be deadly, but they're two distinct natural weapons.

The terms 'venom' and 'poison' are often used to mean the same thing: a toxic chemical produced naturally by an animal. However, the key difference between them lies in their delivery.  

Dr Ronald Jenner, venom evolution expert at the Museum, explains the similarities and differences between these two fascinating toxic substances.  

What's the difference between venomous and poisonous?

A fundamental difference between venom and poison is how the toxins enter the body of the victim.

Ronald's rule for telling the difference is straightforward: 'If you bite it and you die it's poison, but if it bites you and you die, that's venom,' he says.

The hallmark of venom is that it's introduced via a wound. It can be injected through a number of means, including teeth, a sting, spines or claws.

'Poison is different as there is no wound involved. It can be absorbed into the bloodstream through the skin, inhaled or ingested,' he says.

A lionfish

The venomous dorsal spines of a lionfish are used for defence. Although the toxins are not deadly to humans, the venom causes extreme pain and other uncomfortable side effects such as nausea and headaches. © Michael Gäbler via Wikimedia Commons

Why venom needs a wound

The reason venom requires a wound for application, but poison doesn't, boils down to the difference in chemical composition.

'Poison has very small chemical molecules that can easily pass through your skin. The molecules of venom are too big to be absorbed, so they have to be injected,' says Ronald.

Although possible, drinking venom is certainly not advisable. Even the smallest ulcer or cut anywhere in the mouth or throat would allow venom to be absorbed, resulting in the same effect as being injected.

'I wouldn't recommend anyone do it, but this is why it is technically possible to drink venom. It can't be absorbed through tissue, and then stomach acid messes up the peptides and proteins, destroying the venom.'

Poison is usually used defensively or as a predator deterrent. In most cases it is absorbed through the mouth and digestive system.

Venom can be used defensively. But it has a broader range of roles depending on the animal using it. Some harness it as a tool for hunting, whereas others use it in parasitism or in competition with others of its own species.

Double threat

Some species are both venomous and poisonous.

A cobra spitting venom into the air

Cobras [pictured] are best known for their spitting behaviour. Other species, such as the closely related rinkhals (Hemachatus haemachatus), and the red spotted assassin bug (Platymeris rhadamanthus) choose to spray their venom. © Stuart G Porter/ Shutterstock

'The spitting cobra bites its prey so it is paralysed when the cobra eats it. But it also spits. If that lands in your eye it can cause blindness and horrible pain. That venom is now by definition a poison, because it is absorbed rather than injected through a wound,' explains Ronald.

The blue-ringed octopus makes its own venom like other squids and octopuses.

But the deadly nature of this cephalopod comes from tetrodotoxin (TTX), a poison acquired from bacteria that live in various places in the body, including venom glands.

'You sometimes find drowned green sea turtles that have been grazing on seagrass and have accidently eaten one of these tiny octopuses, which paralyses them.'

TTX can act as either a poison if a predator eats the octopus, or as venom if injected through a bite.

'The venom they naturally produce isn't that powerful, but the tetrodotoxin from the bacteria blocks the transmission of nerve impulses to muscles, and the diaphragm paralyses, causing suffocation.'

A blue-ringed octopus on the seafloor

The blue-ringed octopus steals tetrodotoxin from bacteria living on and in its body, making it venomous and poisonous. This technique is also used by other animals, including some newts, flatworms and arrow worms. © Chanwit Polpakdee/ Shutterstock

Painful doesn't always mean fatal

Not all venoms and poisons are fatal to humans. An envenomation can just be painful, as the substances may be being used as a deterrent.

The bullet ant is regarded as having the most painful sting of all insects. The pain can last up to 24 hours, but a human victim is likely to walk away otherwise unharmed.

Bees and wasps can both provide an uncomfortable sting, but for the most part, neither is deadly - except in cases of anaphylactic shock, an extreme allergic reaction to the venom.

Similarly, some poisons will cause swelling, nausea or other unpleasant side effects if the toxins are absorbed.

Venom resistance

Some animals are so frequently at risk from venom and poison that they have developed a total resistance to them.

Meerkats prey mainly on insects but are also known to feast on lizards, snakes and spiders. Because of their varied diet, they tend to come up against some venomous bites and stings.

Meerkats are part of the mongoose family (Herpestidae), several members of which have evolved resistance to venom. This means they can freely hunt venomous prey with limited risk.

A golden poison frog

The golden poison frog (Phyllobates terribilis) uses its bright colouring to warn predators of its particularly potent poison, which is powerful enough to kill humans © Brian Gratwicke/ Wikimedia Commons

Almost all animals have receptors that transmit chemical messages around the body. Venom works by binding itself to these receptors, blocking vital impulse conduction pathways that allow the body to function normally, such as nerve-muscle communication.

Animals that have developed venom resistance have evolved mechanisms to stop the toxins from binding to the receptors. This results in an animal that can withstand venom with little or no side effect.

So far scientists fully understand venom resistance in only four mammals - mongooses, honey badgers, hedgehogs and pigs - as well as several snakes.

The golden poison frog is one of the most toxic animals on Earth, deadly to almost all animals except one. Their skin is covered in a potent poison that prevents nerves from transmitting impulses, rendering muscles inactive.

These frogs' only predators are a single species of snake, Liophis epinephelus, which has developed a resistance to their powerful poison.

But with the enormous variety of animals on the planet, there is a whole world of venom and poisons left for experts to explore, from the toxin cocktails to the animals that might be resistant to them.