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Poisons are substances that can harm organisms. When an animal comes into contact with a poison, the poison interferes with the way its body works. For example, some frogs have poison in their skin. When another animal touches them, the poison damages their nerves. Some snake bites stop blood from clotting. That can cause an animal to bleed to death. Poisons can even be harmful to plants!
This little fat-tailed scorpion is one of the world’s deadliest. It has extremely toxic venom!
Why do such harmful substances exist? They’re actually a natural way for plants and animals to defend themselves. Organisms use poisons to survive. Many spiders use them to capture prey. Many plants use them to defend against hungry animals.
The effect of poison depends on different factors:
The Target
Chocolate doesn’t hurt humans, but it can kill dogs.
The Dose
We need salt to live, but too much can kill us.
Exposure
Some poisons cause harm right away. Others, like lead, build up over time.
The seeds and stems of the cycad plant are an important food for many people. People grind them up into flour. But the plant contains a dangerous nerve toxin. It builds up in the body and can cause loss of muscle control. Lengthy soaking and repeated rinsing makes the flour safe to eat.
Scientists are testing the venom of the funnel-web spider in hopes of developing new treatments for cancer.
How do organisms deliver poisons? Lots of ways! Fangs, spines, stingers, and seeds. Those are just a few delivery mechanisms.
Poisons can be useful to people, too! Scientists have developed many medicines from toxins. For example, aspirin comes from a poison found in willow bark. And they’re studying other toxins to see if they can make them into medicines too.
Where are poisons found?
All over our planet! An enormous number of species are poisonous. These include amphibians, fishes, jellies, insects, bacteria, fungi, and plants. Poisons are useful for survival, so they evolved many times.
- Animal: Some animals, like longwing butterflies and poison dart frogs, eat plants, insects, and other things that make them poisonous. Others make their own poisons. Distinctive markings or bright colors warn predators of mortal danger.
chili peppers
- Vegetable: Over more than 450 million years, plants have evolved an amazing array of chemical defenses. They protect the plants from organisms like insects and bacteria that want to eat them. Defensive poisons are what make mint leaves taste cool and chili peppers burn your tongue. Plant poisons can even defend against other plants! For example, coffee plants poison the soil near them with caffeine. That stops other plants from growing there.
mercury
- Mineral: Some minerals can be toxic. A heavy metal called arsenic, for example, seeps into groundwater from bedrock. Mercury, another heavy metal, gets into soil and air through pollution. It eventually ends up in the oceans and in our seafood.
How do poisons work?
So many different ways!
Poisons that affect nerves are called neurotoxins. There are many kinds of neurotoxins. For example, strychnine is a neurotoxin found naturally in the Strychnos tree in Asia. It stops nerves from carrying signals properly. So does mercury, a heavy metal.
Strychnos tree
castor beans
Poisons that affect the way cells work are called cytotoxins. That’s how ricin (from castor beans) and arsenic, another heavy metal, do their damage.
American
medicinal leech
Poisons that affect the blood are called hemotoxins. Hemotoxins found in leech saliva stop blood from clotting. So do hemotoxins found in the spines of a Lonomia caterpillar. And so do many snake venoms.
white-lipped pit viper
Poisons that destroy muscles are called myotoxins. Some snakebites harm several different parts of the body. That’s because their venoms are a mix of neurotoxins, myotoxins, and hemotoxins.
How do we use poisons?
Sometimes what makes things toxic is also what makes them useful. For thousands of years, humans have used natural poisons to kill pests and weeds. We even use natural poisons to make our foods taste better. Do you like mint, vanilla, cinnamon, or chili? Those are some of our favorite flavors that plants use to repel insects.
mint
cinnamon
Gila monster
And poisons can be great medicines. For example, cone snail venom paralyzes prey painlessly. That makes it useful in medicine. The toxins block pain signals and provide powerful relief. An anti-cancer medicine started as a poison from yew trees. A medicine to treat diabetes comes from Gila monster venom. And those are only a few examples. The search for new medicines from natural toxins has barely begun.
Image Credits:
banner, beetle, poison bottle, snake, CC-BY-SA; Yellow Fat Tailed Scorpion, Shutterstock; chocolate bar, iStockphoto; salt shaker, iStockphoto; lead, iStockphoto; cycad illustration, CC-BY-SA; funnel-web spider, Can Stock Photo; golden poison frog, © AMNH/T.Grant; chili peppers, Håvar og Solveig/CC BY 2.0; mercury, iStockphoto; Strychnos nux vomica, by Franz Eugen Köhler via Wikimedia Commons / public domain; castor beans, Adam Freidin/CC BY-NC-ND 2.0; American medicinal leech, courtesy of Mark Siddall; white-lipped pit viper, Tontan Travel/CC BY-SA 2.0; mint leaves, iStockphoto; cinnamon sticks, Kobiz7/CC BY-NC-ND 2.0; Gila monster, Carla Kishinami//CC BY-NC-ND 2.0.