Venomous snakes are truly fearsome animals. Every year, about 100,000 people are killed by snake venom around the globe. In contrast, the animal kingdom has produced a few exceptional animals that can resist venom. With impressive resilience, they can shrug off the effects of a snake bite as if nothing happened.
Certain animals have evolved to be near-immune to snake venom. These include the California ground squirrel, domestic pig, hedgehog, and honey badger. Interestingly, several have not only developed venom-resistance – but a resistance unique to them. A honey badger has thick skin, but mongooses have cell-coding to repel venom. Likewise, a hedgehog pairs its own bacteria and spikey defenses with blood-based antivenom.
Prey and predator animals each build venom resistance in different ways. This helps suit their unique needs when escaping or hunting snakes. Scientists understand a great deal about how snakes cause harm with their venom. However, mystery still shrouds exactly how immunity works. A few interesting workarounds – like using horses – helps to advance studies on venom-resistance.
Venom Resistance in Prey Vs. Predators
To appreciate the animals themselves, we must first understand how uniquely this resistance develops. In fact, an animal’s status as prey or predator can influence how their venom-resistance works.
Snakes hunt many animals. To match this, venomous snakes also have predators of their own. It would be impossible for these predators to attack, kill, and eat snakes unless they could weather the fight. In fact, predators of venomous animals are more likely to develop immunity compared to prey animals present in that same area.
It’s theorized that food scarcity motivated this evolutionary trait. If the mongoose, for example, was unable to hunt snakes, its feeding options would be far more limited. In response, this species developed immunity over time and out of necessity.
In this vein, you’ll find venom resistance is different for prey vs. predators. With predators, it’s developed to contend with certain situations. For example, fighting the snake, not fleeing. In contrast, prey mostly need to survive the first bites so they can escape.
This is displayed in the hedgehog’s limited resistance. It’s intended to keep it alive while its spines deter the snake. Meanwhile, a honey badger’s thick skin helps it in the long, sometimes drawn-out fight against snakes.
How Are Animals Immune To Snake Venom?
Scientists are still exploring the ways that venom immunity develops. Some animals have it, and others don’t. While its exact molecular or genetic markers are still a mystery, we do understand some factors to venom immunity.
Antivenom, also known as antivenin, is a term used to refer to any compound that can neutralize venom. When it occurs naturally, like in various animals, this is often due to mutations present in the blood. Certain receptors block off venom from binding to the blood, which stops it from affecting the body.
Antivenom is best for when venom still gets into the bloodstream. At low enough dosages, the animal will continue to go on with its day.
In contrast, there’s a more resistant form of antivenin blood. This is found in the mongoose. Certain mutations in this species’ cells make it almost entirely immune to snake venom.
Unlike other animals with antivenin blood, venom simply bounces off a mongoose’s cells. This is outlined in an article published in the Proceedings of the National Academy of Sciences. The average creature (or human) would experience a breakdown in red blood cells, proteins, or enzymes. In contrast, a mongoose seems to experience no such effects.
Interestingly, this is similar to the mutation that snakes themselves demonstrate. We don’t yet understand this protection fully. Even still, scientists hope that uncovering the root will help to develop more effective antivenoms for humans.
Really Thick Skin
Venom, unlike poison, has its greatest impact once it enters the body. Skin contact alone will not cause damage, irritation, or rashes of any kind. This means that bites that do not puncture are rather useless. Snake hunters use this to their advantage.
The honey badger is a prime example. A snake’s fangs will struggle to pierce the thick dermal layer. It may take several bites to do so. Matched to its general immunity, when the honey badger limits the number of bites that actually make contact, it creates a near-limitless advantage.
You can also see this in prey animals – like the domestic pig. What the pig lacks in flexibility, it compensates with a strong protective layer.
Animals That Can Survive A Snake Bite
Without further ado, let’s explore the animal kingdom’s greatest answers to snake venom.
Honey badgers are the poster child of venom immunity. Also known as the ratel, honey badgers are a mammal commonly found in Africa, Southwest Asia, and the Indian subcontinent. This species has a long, black body. That’s matched to a small, flat head with a short muzzle, and topped off with small eyes and ears. Its legs are short but study, with sharp claws used to fight viciously.
These small, fuzzy-looking mammals sure aren’t pettable. But would you imagine that snakes fear them too? Honey badgers are impressive snake predators. They also regularly take on animals much larger than them, such as lions and hyenas.
The honey badger is omnivorous, with one of the most varied diets in the weasel family. It’s known to eat berries, roots, and bulbs. It also prefers small animals like insects, birds, and rodents. Of course, this badger sometimes aims for larger, more challenging animals, like lion cubs and snakes.
What Gives Honey Badgers Venom Immunity?
Honey badgers have a double resistance to snake bites. Their blood can develop antivenom, which easily stops any bites from venomous snakes. Aside from their blood, it can be hard to land a bite on this animal in the first place. Because of the thickness of their hide, it’s extremely difficult to pierce any part of a honey badger’s skin.
Other than snakes, honey badgers are immune to bee venom. After all, honey badgers take their name from their love of honey. They regularly climb up trees and take it straight from beehives. While doing this, bees will sting them repeatedly. Unperturbed, these fearless animals simply continue eating as if the insects weren’t there at all.
In the regions these badgers call home, it’s common to find snakes of every shape, size, and toxicity in these very trees. No wonder badgers need two kinds of venom resistance!
Hedgehogs are often regarded as one of the cutest animals in the animal kingdom. Measuring at between 5 to 14 inches, they weigh about 2 pounds, even when fully grown. Despite their cute features, though, this small mammal can pack a punch.
Hedgehogs are easily recognizable by the spines on their back. These are hollow and made of the same material as hair: keratin. The spines are not poisonous, but are often coated in bacteria that hedgehogs cultivate in their mouths. Depending on the subspecies, hedgehogs may be able to eject a few spines when attacked.
If threatened, hedgehogs always prefer to roll up into a ball. It may appear simple, but this interesting defense mechanism is often enough to defend hedgehogs from larger predators. Within this a tight ball, the spines on the hedgehog’s back point defensively outwards. In this way, hedgehogs can protect other parts of their body that are not covered in spines. These include the face, legs, arms, and belly.
Some hedgehogs do more than just go on the defensive, however. A few subspecies are known to attack with their spines. That’s accomplished by rolling into a ball and ramming themselves against attackers. For these kinds, hiding in a ball is used as a last resort.
What Gives Hedgehogs Venom Immunity?
Considering their defense mechanism, it’s no surprise that hedgehogs have developed an immunity to snake venom. After all, when balled up, hedgehogs can only rely on their spines. If attacking snakes are dedicated, they’ll accept the painful stabs in exchange for biting the hedgehog. With immunity, hedgehogs can just safely wait out the attack.
This immunity comes from the protein erinacine. It can be found in the hedgehog’s muscular system. With that said, because of their size, hedgehogs can only handle a small amount of snake venom. A single snake bite – especially from more fatal species, like vipers – is sometimes enough to kill a hedgehog.
Additionally, bites to areas that do not have spines are more fatal. One bite to the face, belly, or extremities can be enough to kill this animal. That’s mainly from damage caused by the fangs to soft, unprotected flesh or organs.
Interestingly, hedgehogs are one of four mammals that have immunity against the a-neurotoxin. Other mammal groups include pigs, honey badgers, and mongooses.
An unlikely candidate for venom-resistance is the domestic pig. Also known as the swine or hog, pigs are well-known farm animals. They have a relatively long and pointed head, with short, stubby tails, and pink flesh. When full-grown, an adult pig can measure up to 6 feet long, and weigh between 100 to 700 pounds, depending on the breed.
While a popular animal, it’s not always thought of as tough or hardy. However, pigs are a subspecies of the wild boar, which is an incredibly durable animal. In fact, domestic pigs may have been domesticated from wild boars, with remains dating earlier than 11,400 years ago.
What Gives Pigs Venom Immunity?
Like the mongoose, honey badger, and hedgehog, the domestic pig has a natural resistance to the a-neurotoxin in snake venom. Specifically, pigs have a mutation in the receptors that respond to the a-neurotoxin. The mutation prevents the neurotoxin from binding, which effectively renders the venom useless. This allows them to be resistant to the venom of many different species, including rattlesnakes.
Additionally, the thick layer of fat on a pig’s body also helps to ward off snake venom. More often than not, a snake’s bite is unable to penetrate the fat. This stops the venom from reaching the bloodstream, where it does the most damage.
Interestingly, pigs aren’t just resilient to snakes. They’ve been known to actively try and kill these reptiles on sight. It’s believed to be caused by maternal instincts, since snakes prey on the juveniles of many species. Juvenile pigs are susceptible to snake venom, as their immunity only develops with age.
Because of this, many pig farmers have reported their pigs stomping snakes that have slithered into the pen. With that natural advantage, several farms use their swine as a guardian against reptile invaders. Cats and guinea hens are two other favorites for the job, but they rely on dexterity and stamina to fend off snakes. Pigs simply outclass them with durability and immunity.
California Ground Squirrel
When it comes to venom-resistance, not everyone thinks of squirrels. However, squirrels can do more than just defend against snakes. They match immunity with several wily defense mechanisms.
Squirrels are a part of the Sciuridae family, which includes small and medium-sized rodents. Other animals in this family include:
- Tree squirrels
- Ground squirrels
- Flying squirrels
- Prairie dogs.
Within the squirrel family itself, there can be many variations. Each has their own appearances and defense mechanisms. Perhaps the most interesting of these defense mechanisms belong to the California ground squirrel.
How Do California Ground Squirrels Defend Against Snakes?
California ground squirrels are partially immune to their main predator, rattlesnakes – but that’s just the beginning. They are known to pick up a rattlesnake’s shed skin. They chew up this skin, then lick themselves and their pups. This allows them to smell just like rattlesnakes. Brilliantly, it camouflages them from their biggest predator, who hunts primarily by smell.
Squirrels don’t just stop hiding. They are known to go on the offensive, too. California ground squirrels have the ability to heat up their tails at will and shake them aggressively. They often do this when faced with a rattlesnake, which can scare away the feisty creatures. Indeed, it seems that two can play at the tail-rattling game.
This tail-shaking also emits an infrared signal. This radiation can be particularly scary to rattlesnakes, which are sensitive to infrared. That’s supported by a study published in the Proceedings of the National Academy of Sciences.
In this study, infrared was measured as emanating from the tail-flagging display of the California ground squirrel. In particular, when provoked by a rattlesnake. If faced with gopher snakes, which aren’t sensitive to infrared, the squirrels did not use this technique. Additionally, the study tested a robotic squirrel that deployed infrared signals when tail-flagging a rattlesnake.
As expected, the rattlesnakes were more defensive when the robot gave off infrared signals, but less-so when it didn’t. Though it appears cowardly, this is certainly a fascinating win for the squirrel. Of course, even if it weren’t so effective, squirrels still have their venom resistance to fall back on.
Last, but not least, is the humble mongoose. Despite how it looks, the mongoose is perhaps one of the hardiest animals when pitted against a venomous snake. They’re prolific hunters of these reptiles, with no real preference for one species over the other. In many cases, both modernly and historically, they have been used as a method of population control. If an area has snakes in abundance, mongooses can easily dampen the numbers.
Mongooses are small carnivorous mammals. They’re native to southern Europe, Asia, and Africa. They have long bodies, with short legs, long faces, and short ears. Of course, their most defining feature is their long, tapered tail. Despite their weasel-like appearance and skinny bodies, these animals can easily take on a venomous snake.
What Gives Mongooses Venom Immunity?
Mongooses have a mutation in their cells that allows them to resist snake venom. Unlike other animals, however, mongooses are extra-resistant. The venom simply ‘bounces off’ their receptors. This is because of a glycoprotein that coats the cells, rendering the venom ineffective.
As mentioned, they’re one of the greatest hunters of snakes. Because of this, mongooses have yet another advantage. Not only is their blood extra venom-resistant. Mongooses are quick and agile. If forced to wrestle a snake, they can easily keep up with the twists, bends, and thrashes.
That leaves snakes at a disadvantage, struggling to wrap around or hold onto their predators. In fact, king cobras are known to avoid mongoose for this very reason. Once in their grip, snakes will very rarely escape – and certainly can’t flee quickly enough.
Venom-Resistant Vs. Venom-Immune Animals
Although used interchangeably, venom-resistant is not the same as venom-immune.
An animal that’s generally considered venom-proof can survive being injected with venom. In fact, they may shrug off a dose that would immediately kill any other animal. However, they still may die from a large or constant dose of venom. Bites to certain areas may also kill them, as demonstrated with the hedgehog.
In the wild, this is an unlikely scenario. Animals of every kind possess a fight or flight instinct. When bitten, most will flail, run, or even claw and bite back. This prevents snakes from dosing their victims indefinitely. That’s especially true if the venom doesn’t take hold, weakening the prey.
After all, that’s why venom exists – to give snakes a killing advantage. Without it, they rely solely on strength. As we see with the mongoose, not all snakes can count that as a winning skill.
Because of this ‘immune-but-not-quite’ technicality, many scientists and animal researchers use the term “venom resistant” instead. In practice, however, one can consider most venom-resistant animals to simply be venom-immune. They can mostly shrug off incredible doses – or, in the worst cases, at least survive. A lethal dose is unlikely – or for some animals, like the honey badger, nearly impossible. It would require almost clinical-level exposure to take them out.
What Causes True Immunity In Animals?
To understand true venom immunity, we must first understand venom. Snake venom works by releasing toxic proteins and enzymes into the body. For snakes, this is produced through modified saliva glands. Using a saliva-venom covered bite, they quickly inject the toxins into their victim’s:
While the toxic protein causes the most damage, the enzymes are what speed up the deadly effects of snake venom. By demolishing the chemical bonds between molecules, venom can result in:
- Ruined muscle control
- Dropping blood pressure
- Damaged red blood cells
The Evolution of Immunity
As of now, scientists don’t quite understand how venom resistance or immunity works in certain animals. However, according to an article in Integrative and Comparative Biology, some believe it starts with the molecular evolution process. Snakes developed their intense venom through “positive selection, gene duplication, exon shuffling,” and other factors. Meanwhile, venom-resistant animals developed their ability to fight off those effects, more or less, out of genetic necessity. Their species would struggle or cease to exist unless they did.
The effects of venom will vary, depending on the snake. Some contain powerful neurotoxins, while others do not. It also depends on the dose of venom, and the body weight of the creature being bitten. In general, the effects may include:
- Paralyzed muscles
- Thickened blood
- Shut down of nerve function
- Damage to the heart and, thereby, induced cardiac arrest
Animals with resistance to venom belong to an extra special category. These creatures evolved over thousands of years to thwart a toxin meant to kill, disable, and weaken. As we learned above, however, some animals don’t just stop at being venom resistant. Some actively use this resistance to fight back – turning the tables on who is prey and predator.
Why Are Horses Used To Make Antivenom?
You may be surprised to learn horses are a leading tool in creating antivenom. Despite not being very resistant themselves, they help humans around the world survive venom-filled bites. This is because of their body weight, ability to create resilient antibodies, and their domestic nature.
Despite being fragile in many ways, horses are excellent at developing antibodies. After snakes are milked for their venom, horses are exposed to this venom. At small enough dosages, this doesn’t hurt the horse at all. Once a horse has built up a tolerance, researchers can extract the newly developed antibodies. These are then used to create antivenom, which can be administered to snake-bite victims across the globe.
Part of their resilience comes from their body weight. A horse can weigh between 840 and 2,200 pounds, depending on its breed. If injected with a small amount of venom, this mass helps to balance out the true impact of the toxins. Since it can’t overwhelm the horse’s system, its body can adapt and build a resistance. The end result will be powerful antibodies, making the horse stronger against future exposure to venom.
Finally, horses are great test subjects because they’re well-domesticated. Amicable to humans, they’re less likely to retaliate at the sight of a needle. They’re easy to keep, easy to care for, and simple to harvest antibodies from. In contrast, sharks are another great candidate for developing antivenom. Unfortunately, though, they’re much harder to work with.
Are Snakes Immune To Their Own Venom?
Snakes are indeed immune to their own venom. This is helpful for many reasons.
Venom Is Secreted Through The Same Glands That Produce Saliva.
If they were not immune, snakes would risk swallowing a toxic substance regularly.
Accidental Bites Happen
Struggling with prey often involves a great deal of thrashing and tumbling. This can make it easy for snakes to accidentally bite themselves as they try to inject more venom into their prey. Without immunity, that would be comically fatal.
Snakes Are Often In Contact With Other Snakes
These creatures are born in clutches. As such, they’re exposed to other venomous snakes regularly as they age. Accidental bites, or full-blown fights, could result in mass death among a batch of hatchlings if they lacked immunity.
Snakes Often Fight During Mating Season
All species of snake work to prove their superiority, or defend their claim, with new mates. This can result in fighting and biting among males. If every bite was lethal, this would quickly bring the mating season to an end (and the species with it).
However, there is a caveat to this.
Are Snakes Immune To All Snake Venoms?
A snake is only immune to the venom of the species it belongs to.
If a snake is bitten by a snake of a different species, it suffers just like any other animal. As mentioned, venom can differ widely between snake types. One species may be resistant to the chemical and molecular structure of their own venom. However, another species could be entirely different. Their body will have no natural defenses against this foreign substance.
Likewise, it’s suspected that part of a snake’s immunity is from exposure. By ingesting its own venom on a regular basis, its body learns how to accept it. The play-bites (and real bites) from members of its own species also help to build a resistance.
This happens with small, safe doses over time. However, a sudden new bite from a different species will not be a gentle introduction to the venom. With no partial immunity, the venom can be heavy enough to kill.