Meet the animals with built-in antivenom
How do some creatures survive being bitten and stung by the most venomous nasties on Earth?
Whether it’s the bite from a viper, a sting from a scorpion or the subtle swipe of a jellyfish, the world’s venomous species have evolved the ability to deliver a killer cocktail of chemicals. However, there are those that have also evolved immunity to their fatal effects. There are roughly three types of venom among the more notorious of the 600 venomous species of snake. Neurotoxins affect the body’s nervous system, blocking communications between nerves and ultimately shutting it down altogether, resulting in paralysis. The second, hemotoxins, bring about a particularly gruesome demise. These toxins attack the body’s red blood cells, making them coagulate to form gelatinous blood clots. Finally, cytotoxins are those that begin to digest the body’s cells before the snake has even swallowed its prey.
As predators and as prey, venomous snakes are formidable opponents, but certain species are able to tackle them head-on without fear. The mongoose is the deadly cobra’s worst nightmare. In order for this snake’s neurotoxic venom to work the toxin must be able to bind with receptors on nerve cells. However, the mongoose’s nerve receptors have mutated in a way that prevents this kind of bind, thus immunising it to their paralysing effects. The mongoose is not alone in its fight against the forces of neurotoxins: honey badgers, ground squirrels and even hedgehogs are among some of the mammals able to endure an otherwise fatal dose of neurotoxin from the fangs of a snake.
The North American opossum is also well-equipped for a battle in the bloodstream with the ability to neutralise the venom of around 12 species of venomous snakes. The western diamondback rattlesnake, for example, is one such species. This snake’s particular brand of toxin is a hemotoxic venom, infiltrating the bloodstreams of their prey or aggressor, hijacking its blood cells and destroying their internal organs and circulatory system. The opossum, however, has a blood cell bodyguard in the form of a chain of amino acids in its blood that are able to neutralise invading venom.
Arguably the world’s most venomous species, the box jellyfish is able to disable and kill many living creatures in seconds. With each tentacle equipped with 5,000 stinging cells, these formidable creatures don’t seem like potential food, yet leatherback turtles feast on jellyfish almost exclusively. Unlike the other mammal antivenom members, leatherback turtles have a physical adaptation to defend against one of the world’s most venomous jellyfish. Lining its thick oesophagus that leads towards its stomach are continuous rows of inward-facing papillae, or protrusions. Made from hard keratin, the same material found in fingernails, the sting of a jellyfish is rendered useless.
The sting of a scorpion can be fatal to many rodents who come in close contact with them. There is one, however, that has baffled researchers for not only its ability to prey on these sting-equipped insects, but to do so unscathed. Native to the southwestern United States the grasshopper mouse has taken a liking to the taste of bark scorpion. Deadly to other animals, when stung the desert-dwelling grasshopper mouse simply licks its paws and finishes its meal. It’s still unclear exactly how the mouse is immune to the scorpion’s sting, though it is thought to be related to a protein released at ion channels on the rodents’ nerve cells. By binding with the injected toxin, these proteins are thought to actually create a numbing effect, reducing any pain felt by the mouse.
Snakes not only have to fear the threat of attack from land, but also the skies. Winged kung-fu killers, secretary birds have developed a martial arts method to feast on snake flesh. While not strictly anti-venom – they do not possess an internal immunity to tackle snake venom – these birds avoid bites by delivering several rapid-fire blows to a snake’s skull. One study found that on average it took just 15 milliseconds for the bird to strike the snake’s head. Delivering a 20-kilogram-force blow to the head, secretary birds are able to disarm a venomous snake without feeling the force of their bite.
This article was originally published in How It Works issue 123
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