TOXIC, VENOMOUS AND POISONOUS ANIMALS

VENOMOUS, POISONOUS AND TOXIC ANIMALS

Diversity of venomous animals and their venom apparatuses: A) The starlet sea anemone, Nematostella vectensis; B) cone snail, Conus legatus, with extended proboscis; C) African rain spider, Palystes sp, showing chelicerae; D) scorpion Parabuthus sp with stinger; E) platypus, Ornithorhynchus anatinus; F) the Mediterranean banded centipede, Scolopendra cingulata, with forcipules; G) bluespotted stingray, Taeniura lymma, with spines on the tail; and H) spitting cobra, Naja mossambica, spitting venom from its fangs [Source: Researchgate]

Venomous is the correct term for animals with poison. If you call them poisonous technically that means they are poisonous to eat, like poisonous mushrooms. Ethan Freedman told Live Science, The terms "venom" and "poison" are not interchangeable. Venom is injected directly by an animal, whereas poison is delivered passively, such as by being touched or ingested. "If you bite it and you get sick, it's poisonous. If it bites or stings you and you get sick, then it's venomous," said Jason Strickland, a biologist at the University of South Alabama who studies venom. In a research article published in 2013 in the journal Biological Reviews, scientists proposed a third category of natural toxins: the "toxungens." Toxungens are actively sprayed or hurled toward their victim without an injection. For example, spitting cobras can spew toxins from their fangs. [Source: Ethan Freedman, Live Science, March 27, 2023]

Ethan Freedman wrote in Live Science: Venom alone has independently evolved more than 100 times, in creatures as varied as snakes, scorpions, spiders and cone snails, Strickland said. They're also pretty common — by at least one estimate, around 15 percent of all animal species on Earth are venomous. And many of these natural toxins are made up of compounds that work in different ways. For example, the neurotoxins (like those found in mamba snake venom) assault the nervous system, while the hemotoxins (like those found in copperhead snake venom) wage war on an animal's blood. Some Mojave rattlesnake (Crotalus scutulatus) venom actually has both neurotoxins and hemotoxins, making these venomous animals potentially "a very unpleasant species to get bitten by," Strickland said.

Yet some nontoxic creatures have managed to keep pace with their toxic adversaries. Opossums seem to have developed resistance to snake venoms, and grasshopper mice actually appear to get a pain-relieving effect from the stings of bark scorpions. If the distinctions between poisons, venoms and toxungens seem a little arbitrary, it's because they sort of are; in some languages, there is only one word for both "venom" and "poison." In Spanish, for example, both are translated as "veneno," and in German, both are translated as "Gift."

Toxins Found in Venomous and Poisonous Animals

Poison and venom don't always work the same way. For example, venom won't necessarily hurt someone unless it enters the bloodstream, according to the University of Florida Department of Wildlife Ecology and Conservation. No matter how they're delivered, these toxic chemicals are highly effective weapons in the evolutionary arms race between predator and prey. And in some cases, a single animal can employ its toxins on both offense and defense.

Toxic pretty much means the same thing as poisonous and a toxin is a poison. Biologically, the toxic substances found in animals is incredibly diverse. Different attack modes can reflect how the toxin is used. For example, venomous ants often use their venom as a defense mechanism, so it causes immediate pain to banish intruders. Snake venom, by contrast, incapacitates its victim so the snake can feed, Strickland pointed out. Meanwhile, some poisonous animals can cause immediate death if ingested, such as poison dart frogs in the genus Phyllobates. These creatures use batrachotoxin, which impairs electrical signaling in the body, effectively stopping cardiac and neuronal activity. Any predator that eats them won't live to eat another poison frog.

Powerful toxins (lethal dose): 1) anthrax (0.0002); 2) geographic cone shell (0.004); 3) textrodoxotine in the blue ring octopus and puffer fish (0.008); 4) inland taipan snake (0.025); 5) eastern brown snake (0.036); 6) Dubois’s sea snake (0.044); 7) coastal taipan snake (0.105); 8) beaked sea snake (0.113); 9) western tiger snake (0.194); 10) mainland tiger snake (0.214); 11) common death adder (0.500). Lethal doses is defined as the amount in milligrams needed to kill 50 percent of the animals tested.

How Animals Attain Their Toxins

regulatory elements and mechanisms detected in different animal lineages that influence transcriptional and posttranscriptional regulation of venom genes

Bioexplorers looking for potentil drugs in the animal world, Robert George Sprackland wrote in Natural History magazine, “are well advised to seek the help of seasoned systematists — taxonomists with a solid grounding in the evolution and natural history of organisms. For one thing, the chemicals that a species produces by itself must be distinguished from the ones it gets from its diet or its environment. And if the target animal isn’t ingesting the right bacteria or other toxin producers at the right time, bioexplorers may not be able to extract the chemicals they want. [Source: Robert George Sprackland, Natural History magazine, October 2005]

Some toxin carriers, for instance, including sea slugs and puffer fish, feed on toxic species only seasonally. Bioexplorers once noted, to their dismay, that long-term-captive and captive-bred dart-poison frogs produced less potent poisons than their wild counterparts — or even no poisons at all. Systematists were able to resolve the puzzle. Many precursor chemicals for the poisons come from specific prey insects. Deprived of their natural prey, most of the frog species became harmless.

Systematists can also save both time and money once a particular species has been identified as a source of a particular biomolecule. It is then well worth determining whether a close relative of the species might produce an even more useful version of the molecule. But related species — particularly the ones belonging to the so-called lower taxa — may be hard or impossible to pinpoint without the knowledge of a qualified systematist. Ranging even more widely through the tree of life, systematists might also help show the way to multiple, alternative sources of a specific biomolecule.

Tetrodotoxin — The Toxic Chemical in Japanese Pufferfish

Robert George Sprackland wrote in Natural History magazine: Tetrodotoxin, also known as TTX, is a powerful nerve agent, first identified in the tissues of certain puffer fish of the family Tetraodontidae. In Japan the fish is best known for those puffers belonging to the genus Fugu, an expensive, high-thrill delicacy, which is served after the poisonous bits have been skillfully carved away — or so the diner hopes — by specially licensed chefs. (Alas, there are some 50 to 150 accidents each year, in which the Fugu feast becomes a last meal.) [Source: Robert George Sprackland, Natural History magazine, October 2005]

After tetrodotoxin was identified in puffers, it started turning up in a variety of places around the globe. In 1982 the ethnobotanist and independent scholar Wade Davis announced that TTX is a major component of the voodoo elixir that turns people into zombies. (A person in a zombie state cannot move, but is fully conscious of everything around him.) TTX was later identified in the skin secretions of the American rough-skinned newt (genus Taricha), an amphibian often kept as a pet, and in the venom of Australia’s tiny blue-ringed and blue-lined octopuses (genus Hapalochlaena).

Perhaps most remarkably, it also turned up in the feathers of two genera of birds, Pitohui and Ifrita, in New Guinea. The source of the toxin turned out to be bacterial. Such microorganisms readily disperse across great distances and throughout a variety of habitats. Thanks to studies by systematists, bioexplorers no longer need to find a particular species of puffer fish in order to obtain TTX.

Toxic Animals as Sources of Drugs

Robert George Sprackland wrote in Natural History magazine: Animals, like plants, have long been known as a source of a vast array of chemicals, many of the with great potential for human use. Many frogs, for instance, secrete compounds through their skin that have powerful antibiotic properties, enabling them to thrive in stagnant water teeming with pathogens. Clown fish wear a coat of slime that informs the anemones with which they live that clown fish is not on the anemone menu. Corals exude chemicals that protect them from sunburn at low tide; derivatives of those chemicals are already being marketed as sunscreens. Even compounds from sponges have led to valuable drugs: acyclovir, a treatment for herpes, and cytarabine, for a kind of leukemia. [Source: Robert George Sprackland, Natural History magazine, October 2005]

The chief attraction of animal biomolecules, particularly the toxins, is their staggering potency: they are often hundreds of times more powerful than plant compounds that deliver a similar medicinal effect. For example, the analgesic alkaloid epibatidine, derived from South American dart-poison frogs, is about 200 times more powerful than an equal amount of morphine, derived from poppy flowers.

But why seek potency for its own sake? Why not play it safe, and simply use more of some less potent agent? After all, it goes without saying that the more powerful the toxin, the less of it is needed to achieve its effect, and so the greater the risk of an overdose. The answer lies in the highly specific way that the most potent animal toxins attack certain kinds of cells or cellular processes. That very specificity of chemical action is often a highly prized medicinal property. It enables a drug to attack the site of a disease — a highly localized cancer, for instance — without crippling side effects. A precisely targeted drug can also act as a carrier for some other drug, bringing the second agent to the part of the body where it can do the most good. Hence, investigators reason, pharmaceuticals derived from modified but potent toxins may prove useful in targeting drug treatments.

Many animal toxins, for instance, have evolved that exploit the vulnerability of nerve cells. That makes sense — from the point of view of the attacker — partly because nerve cells, in most cases, cannot be replaced or even repaired. But nerve cells have two other liabilities that make them particularly vulnerable to even small-scale structural problems. First, they can be shut down by minor interference with any one of several critical components [see illustration below]. For example, a toxin could block neurotransmitter sites either upstream or downstream from the synapse between two nerve cells, making it impossible for a nerve impulse to travel across the synaptic gap. A toxin could bind to the neurotransmitter molecules themselves, rendering them useless.

Nerve cells can be attacked by animal toxins in any of several ways, as shown in the schematic diagram. Nerve signals depend on the opening and closing of ion channels along the nerve axon, and on a mechanism that enables neurotransmitter molecules to cross the synapse, or gap between upstream and downstream cells. Interference with any one of the mechanisms can cut off an entire signaling pathway.

Or a toxin could block the channels that enable sodium and potassium to pass through the nerve-cell membrane, and thereby halt a neuroelectrical impulse along the length of each nerve cell. Finally, a toxin could degrade the myelin sheaths that insulate the axons of a nerve cell, causing the nerve impulses to lose strength and dissipate.

The second liability, related to the first, arises simply because part of each nerve pathway is usually made of a single strand of nerve cells in sequence, like the links in a chain. If any single nerve cell is shut down, the entire pathway is neutralized. That’s why the system is so readily sabotaged by minute doses of highly target-specific animal neurotoxins. In some cone shells, for instance, the venom needed to kill those dozen adult humans would fit on the head of a pin.

Because a given toxin may target only a specific section of a particular kind of nerve cell — say, the myelin sheath of cardiac nerve cells — bioexplorers have to screen many toxins to identify which ones attack which targets. Suppose, for instance, screening leads to the identification of a toxin that attacks myelin. That toxin then becomes a key factor in a strategy for repairing some of the damage caused by myelin-degenerative disorders, such as multiple sclerosis.

One way to use the toxin might be to modify or remove just its toxic part, while leaving the myelin-seeking part intact. Then, in place of the toxic part, the bioexplorer might substitute a therapeutic chemical agent, which could restore or mimic the function of myelin. Because the newly engineered drug would be so target-specific, virtually all of it could act only within the nerve cell’s axonal region, making it an efficient fix in small doses. Similarly, other drugs might be designed to retard or alleviate the symptoms of diseases such as Alzheimer’s and Parkinson’s.

Why Venom Attracts Scientists

Wilson da Silva wrote in Australia Geographic: Venom is becoming increasingly attractive to medical researchers and it’s easy to see why. “One of the most diverse, versatile, sophisticated and deadly biological adaptations ever to have evolved on the planet,” is how biologists Ronald Jenner and Eivind Undheim describe it in their book Venom: The Secrets of Nature’s Deadliest Weapon.

“A venom,” they write, “acts more like a battalion of snipers than a machine-gun loaded with one type of bullet. Because the most complex venoms contain hundreds or even thousands of distinct components, they are able to overcome the defences of almost any victim. Moreover, venom toxins act as self-guided bullets.” [Source: Wilson da Silva, Australia Geographic, January 28, 2021

This sort of complexity makes venom attractive to scientists seeking to better understand how the human body works. They can use it to tweak the body’s internal machinery to correct problems, fight disease and improve health. That’s because our bodies, like those of most animals, have an astonishing galaxy of components — from multitudes of proteins and enzymes, fatty acids such as lipids, vitamins, salts such as sodium and potassium, trace elements and signalling molecules that all interact with each other, under the control of genes. And all of this works in mostly unknown or little-understood ways.

Having evolved during millions of years to alter or subvert the molecular machinery of so many species — including humans, either deliberately or accidentally — and in a dizzying array of pathways, venoms represent a treasure trove of potential insights into the ways our bodies work.

How Venoms Are Collected

Wilson da Silva wrote in Australia Geographic: In an underground room behind a double steel door is an insectary where some 100 rectangular plastic trays and round takeaway food containers are each filled with a little soil and a single spider. There are various species of huntsman, tarantula, wolf, trapdoor, funnel-web and mouse spiders — just some of the world’s 50,000 named arachnid species — and a collection of venomous centipedes and scorpions. [Source: Wilson da Silva, Australia Geographic, January 28, 2021

Samantha Nixon, a PhD student of Glenn’s, shows me how she milks venom for research. She places a small container with a single Sydney funnel-web at the centre of a larger tub. Taking a long pipette with a thin, hollow extender, she gently pokes the spider around the head, triggering its attack mode, and then swiftly drains its venom gland with one squeeze. Not bad for someone who, she admits, was once an arachnophobe.

It’s not just spiders, snakes and cone snails that yield venom. Researchers are exploring plants too. Back in Irina’s office, a fuzzy-leafed Gympie-Gympie sapling is perched by the window. Irina picks it up to show me the dense hairs on the surface of the leaves, which, if touched, act like hypodermic needles to inject a potent neurotoxin.

In a study recently published in the journal Science Advances, her team reports on the discovery of toxins that had only been seen before in the venom of spiders and scorpions, although their chemical composition is very different. They cause pain in the same way — by modulating sodium channels in pain-sensing nerves — but do so in a way that makes pain that can last for days or even weeks.

Why would a plant evolve a neurotoxin? Irina has no idea. But being a pain researcher means she’s interested in the mechanisms of pain and how we feel it, so she can develop new treatments. That occasionally means being on the receiving end, as she has been with the Gympie-Gympie: “You get redness and weals, it starts to burn, the pain becomes wavelike and can radiate to your lymph nodes, and you get a deep aching sensation in the shoulders,” she recalls. “It’s very strange.”

Pain Research with Animal Venom

Associate Professor Irina Vetter is co-director of the Centre for Pain Research in Brisbane. “Nature has provided us with this amazing library of millions and millions of compounds, and they all do something,” she says. “And if you’re looking for tools to help you understand how sensory nerves function, or how to affect them, venom is just a treasure. Sometimes it’s really unexpected where it can take you. You can actually learn a lot about how pain-sensing nerves work, how the channels are activated, and new ways to modulate them — and hopefully create new treatments.” [Source: Wilson da Silva, Australia Geographic, January 28, 2021]

Wilson da Silva wrote in Australia Geographic: Venoms have already given the world six new drugs, one of which is Ziconotide, derived from a species of marine cone snail and which is highly effective against severe chronic pain. Another nine are presently undergoing clinical trials. Irina says that while Ziconotide proves venom-derived peptide painkillers are possible, it has to be injected into spinal fluid, “which is less than perfect”. Her team hopes to develop easier-to-use painkillers that could be taken once a week or less.

An area of the institute’s focus are the nine different sodium channels in humans — multi-layered biological switches that create and respond to the body’s electrical signals. They are implicated in a variety of diseases including epilepsy, irregular heartbeat and nerve pain caused by trauma, surgery, disease or chemotherapy. One subtype is predominantly in the heart, another almost exclusively in skeletal muscle, and three subtypes are only found in pain-sensing nerves. But Irina’s team has discovered, thanks to scorpion venom, that a subtype for touch sensing also plays a part in pain.

“In pain research, we’re at a stage where cancer research was maybe 30 years ago, where people started to realise, ‘It’s actually way more complicated than we thought’,” Irina says. “If you have cancer, I can chop out a bit of the cancer and study it. If you have pain, I can’t really chop out your pain-sensing nerves to understand what’s going on. So it’s really difficult to correlate pain you’re describing to a molecular mechanism.”

Image Sources: Wikimedia Commons

Text Sources: Animal Diversity Web animaldiversity.org , National Geographic, Live Science, Natural History magazine, Australian Museum, David Attenborough books, Australia Geographic, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The Conversation, The New Yorker, Time, BBC, CNN, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated June 2025