No, we’re not talking about Marvel’s Venom. But when you think about venom, you might think about snakes and stinging insects. But there are plenty of venomous animals you wouldn’t have ever thought of — even mammals, or worms.
Some animals are more toxic than others, and most of them have completely different ways of producing their killer chemical cocktails or using them on their attackers, or prey. Many of the molecular concoctions that have evolved in the animal kingdom are so unique they could be even used to cure human diseases in ways science cannot yet fathom. While there is still more to learn for scientists, here's what we do know so far.
1. Don’t Mistake Poison for Venom
There are two different types of toxicity – poisonous and venomous, according to Tim Lüddecke, head of the animal venomics lab at Fraunhofer Institute in Gießen, Germany. Poisonous animals are animals that have toxins they can secrete passively — like if they are touched or ingested. That’s the case for the poison dart frog of South America: a colorful killer that releases poison through its skin and is considered one of Earth's most toxic creatures.
“On a molecular level, the toxins of poisonous animals are very, very small, because only if they are small, they can be obtained passively in an efficient manner,” says Lüddecke. This is usually most helpful against predators.
Venomous animals, on the other hand, need a method of injection for their toxins to have an impact — through a sting, or a bite, for instance — and their toxins make it straight into the metabolism of the victim so they’re a little bit larger, molecularly speaking. This method comes in handy for hunting, attacking and overpowering prey.
2. Venom Can Help Against One’s Own Kind, Too
Adding to how venom can be used to both fend off predators and attack prey, there is actually a third use for toxins called intraspecific competition, according to Lüddecke.
For example, the Australian platypus often engages in male-on-male combat to win over the mating competition. During their feuds, the male platypus deploys a tiny prick on its back legs to jab their competitor with potent venom and debilitate its opposition through pain.
3. It’s Not Just Biting or Stinging… But Shooting, Too
As the Australian platypus battles and the poison dart frog secrets toxins, other species have a more sophisticated way to use their secret weapon.
“The weirdest venomous animals are in the species where you wouldn’t even look,” says Lüddecke. “Like, there are venomous snails.” He’s talking about cone snails, colorful yet highly venomous sea snails.
What makes them special isn’t just that they are unexpectedly lethal, but that they have evolved extremely sophisticated ways to inject this venom. They don’t have stingers, instead, they have a proboscis through which they shoot venomous arrows, like harpoons, even over a long distance, to paralyze their prey.
“It’s part of the tongue, but it's been weaponized into a harpoon,” says Lüddecke. Two species of this snail have even killed humans, according to the Carnegie Museum of Natural History.
4. The Target Selects The Toxins
While there’s a plethora of methods to distribute venom, there’s also a wide variety of toxic cocktails that animals can create, and a broad spectrum of effects the venom can have on any unlucky victims.
“It always depends on what kind of prey you're hunting, and if you have a high diversity of diet or if you're super specialized,” says Maik Damm, a Ph.D. student of snake venomics at the Technische Universität Berlin. Among venom experts, the consensus is that “the target selects the toxins.”
Many vipers prey on small mammals with a fast metabolism, so they’ve evolved venom that works on the blood system and disrupts coagulation. This causes blood clots in the brain, which leads to rapid strokes and bleeding into the lungs and brain. Other snakes like cobras, for instance, have evolved to deliver venom that disrupts the nervous system’s signal transmissions instead — aka “neurotoxic” venoms. That's because most of these species like to snack away at cold-blooded prey, in which a fast acting venom is needed, else they are quickly gone. Neurotoxins also are highly effective against spiders and other arthropods, in which blood-centered venoms wouldn’t have much effect.
“I think the most important point is venom is not just ‘venom,’” says Damm. “It's so unique from each animal to the other, and this is the biggest challenge to investigate venom.”
The same species of snake in one large country, for example, can have a completely different type of venom according to where it is regionally. Meaning, antivenom that works in one geographic area doesn’t work in another one.
5. Almost All Animal Families Have a Venomous Sibling
There aren’t many reliable numbers on exactly how many species on this planet are toxic, according to Lüddecke. Some researchers estimated that 15 to 20 percent of animals are venomous, but since there’s a huge diversity of poisonous animals — those numbers grow massively.
“Each animal lineage, no matter how weird they are, or how advanced or primitive they are, they very likely have a venomous member,” says Lüddecke. “What we see all over the evolutionary tree of life is that venom has reinvented itself numerous times independently.”
The slow loris, an adorable-looking primate from South East Asia, actually secretes a flesh-rotting type of venom from its teeth when it bites. It is one of the few venomous mammals known to science — in addition to the platypus, the shrew and vampire bats. And just like the platypus, it often uses venom to settle territorial or familial disputes with its own kind.
6. Dinosaurs Might Have Been Venomous
Given this reasoning, of how all animals seem to have at least one venomous member, Lüddecke and his team actually speculate that dinosaurs may have been venomous, too. Although the glands and tissues of dinosaurs have not been preserved throughout history, there may be hints of this on their teeth, according to Damm.
“They have some grooves into their teeth, ones that you can also see on snakes and lizards,” Damm says. “So there are some hypotheses that dinosaurs might also be able to inject some kind of bioactive secretion of mucus or saliva. The hints are relatively big.” However, a lot more research in this field is still necessary.
7. Some Animals Have Lost Their Venom Over Time
Venom is ecologically expensive — it takes up a lot of energy for animals to make their own killer cocktails, meaning they need to be well-rested and well-fed at all times. So, if something changes in an ecosystem and venom is no longer necessary, an animal species might lose its ability to be venomous over time.
“A very, very famous example is sea snakes, which are usually among the most toxic snakes known to science,” says Damm.
Since they were fish eaters at the bottom of the sea, they originally needed venom to kill fish that would have otherwise fled too quickly to catch. Now, at least one species of sea snake has switched from fish feeding to feeding on fish eggs, which are easier to munch on because they can’t run away. Suddenly, they no longer needed venom.
8. Learning More About Venoms Could Massively Advance Medicine
“It depends on how you calculate it, but we have between 11 and 16 drugs on the market that stemmed from animal venoms,” says Lüddecke. “And most of them actually come from reptiles, especially snakes.”
One brilliant example of this, he says, is Captopril, which is based on the toxin from the Lancet Viper from South America, and saves millions of lives every year. Other venomous cocktails are currently under investigation in labs for other diseases and conditions — like recovery after stroke, chronic pain, or epilepsy.
“And these are only the creatures we already have looked in,” says Lüddecke. “But now we finally have the technological methods to also look into the small often overlooked animals.”
Spiders, for instance, are estimated to represent 50 percent of all biomolecules that are present in venoms, but only less than 1 percent of all spiders have been investigated for their venomous properties.
“We now live in the age of biodiversity loss, but we haven't investigated the vast majority of venomous species,” says Lüddecke. “All the components in the venoms are unique to this species, which means every venomous species we lose to biodiversity loss, we could also lose the next blockbuster drug.”