Plants may not be able to do math or post on Instagram, but that doesn’t mean they can’t protect themselves in complex, or even crazy ways. From thorns to chemical cries for help, check out some of the wild ways that plants keep herbivores at bay.
Everybody knows thorns as those sharp, curvy, little spikes on rose stems, right? Actually, wrong, but more on that below. Thorns are sharp branches with leaves growing from their base, which create a nasty surprise for any leaf-hungry animals that come around. The spiky hooks that dot the stem of a rose are actually…
Prickles are sharp bumps that grow from a plant’s epidermis (the fancy word for “skin”). They can grow on bark or leaves and can be super, super spiky. If you’ve ever pricked your finger on a rose, you don’t need any more proof. Prickles will keep bigger animals away, but some bugs are teensy enough to glide between the prickles and have a nice plant snack. Some insect species even mimic the spiky appearance of prickles so that they won’t be attacked while at lunch.
Thorns, prickles, and spines are all related, but if you’ve ever touched a cactus, you probably remember spines the best. They’re super sharp and needle-like to help defend water-filled cacti from thirsty predators and even offer desert-dwelling cacti some shade from the grueling sun—kind of like an umbrella with a sword inside.
If you’ve ever crossed paths with stinging nettle, you probably aren’t quick to forget it. Its lingering sting is due to the fur-like coating of trichomes covering it. You may notice less-painful trichomes on other plants like marijuana, where they look more like a frosty coating than a minefield. These tightly-knit protuberances can absolutely eviscerate any creepy crawlies that decide to come by for a snack. Some species even have glands that will inject a poison after they’ve wounded you, which can paralyze or even kill those that cross its path. Suddenly, the lingering pain of a stinging nettle doesn’t seem so bad….
Idioblasts look harmless, but if you try to eat them, they won’t hold anything back. This type of defense mechanism is only enacted when unsuspecting predators make the first move, and then a set of specialized cells attack with either poisonous chemicals or hidden, sharp crystals. Take, for example, the leopard lily. This common houseplant may look sweet, but if you try to bite into it…. It’ll fire razor-sharp crystals into your mouth, followed by a second course of a poisonous chemical that can cause paralysis. Yikes!
Some plants don’t have any barbed-wire fencing or poisonous bombs to help protect them, and they have to get by on their charm alone. But surprisingly, charm works. Some plants recruit bodyguards to help keep predators at bay and offer up nectar or other foods in exchange for protection. Some types of trees are home to ants species that angrily defend against predators, and even ward off fungus. Not only are they protective, but these ants can also be vindictive: if another plant gets too close, the ants will trim their neighbor’s hedges to keep their property line clear.
If you’ve ever been to a botanical garden, you may be familiar with the mimosa pudica, also known as the “sensitive plant.” You’ll recognize these emo little guys from their signature move: when they’re touched, the immediately recoil and play dead. Watching them react to physical touch is a haunting reminder that even though plants don’t have brains, they’re still very much alive.
If you’re looking for the weirdest, most terrifying, plant defense mechanisms, they’re almost entirely in this category. Many species of plants can release volatile organic compounds (VOCs) when they’re attacked, or even when they’re under stress from drought or infection. These compounds can either be repellant to the predator in smell or by tasting yucky or could even attract their predator’s predators, giving a whole new understanding to “the enemy of my enemy is my friend.”
One wild example of chemical signaling can actually be found in one of your favorite smells. When you get a waft of freshly cut grass, that nostalgic scent is a VOC released by the grass to let nearby friends know it’s under attack. In some ways, it’s kind of like you’re smelling the grass screaming for help. Maybe not so sweet-smelling, after all….
Ah, poison, a classic defense mechanism. This crafty killer can even be tailored to injure specific predators of the plant and is often harmless to friendly creatures. For instance, if you were to touch urushiol (the oily, incredibly irritating sap you might find on poison ivy or poison oak), you’d break out in an itchy, painful rash and likely never touch those plants again. But birds are completely unfazed and could nest in a poison sumac tree without ever being disturbed.