When you hear the phrase “killer hair,” you probably picture a sick mullet - you know, some super cool ‘do.

You’d probably never mistake  it for anything literal. But, if you venture outside the mammalian branch of the tree of life and onto another limb, you’ll find the owners of some truly killer hair.

From switching on the immune system to fighting off insects in the most metal way possible, here’s what plants do with their killer ‘dos. [intro song] So what we’re actually talking about t here are tiny protrusions called trichomes, and a wide variety of plants have them on  their stems, leaves, and other surfaces. While they generally resemble tiny hairs, they come in a handful of varieties– some even secrete chemicals to  help the plant defend itself. And that’s only the beginning of what a bunch of teeny tiny hairs can do.

For example, how does growing more food with less water sound? In a 2017 study in the journal Rice – yes, that’s a journal – researchers bred a gene into a domesticated strain of rice that caused them to grow more  trichomes on their leaves. Their “hairy” strain lost less water during photosynthesis compared to the original, though the plants also got hotter during the day.

The researchers think the extra hairs are affecting something called the boundary layer, which is a layer of air around the leaf, and making it harder for water to pass through and escape the leaf. They hope this could help us develop crops  that resist drought or require less water, which could be useful in the future! But unlike me, if you’ve ever used a blow dryer, maybe you’re thinking, yeah, I know hair traps water.

Don’t worry – I’m just getting started. Trichomes in Arabidopsis, a plant in the mustard family and  darling of the plant genetics world, not only help the plant detect rain – they also help it fire up its immune system. Publishing in the journal  Nature Communications in 2022, researchers showed that trichomes are able to detect the  physical impact of raindrops, as well as other mechanical signals.

Once the trichomes detect raindrops, they send out a pulse of calcium to the surrounding cells . That pulse cranks up the expression of genes that help the plant recognize invading pathogens. But, why rain?

The plant hasn’t detected any  viruses or bacteria or fungi, just a gentle shower. The researchers emphasize that a lot of plant pathogens are spread by raindrops. Just like how your mom told you not to go ou t in the rain or you’ll catch a cold, it seems plants gear up whenever it rains to protect themselves from what comes next.

But while that’s cool, I promised you metal. And now I’m going to deliver. The horsenettle plant uses its hairs to tear apart caterpillars that try to eat it… from the inside.

These plants have spiky, resilient trichomes that pass through the digestive tracts of caterpillars intact. What’s more, they’re wreaking destruction as they go. In a 2017 paper, researchers documented the guts of tobacco hornworm caterpillars being “stretched, punctured, and torn” – their words!

They also showed that caterpillars preferred to avoid diets full of spikes, and it’s no wonder why. They even went the extra mile and showed that silverleaf nightshade, a plant with similar trichomes,  produced similar results. But tobacco, which has different trichomes, didn’t put them off.

There’s at least one strategy even more brutal than ripping apart a herbivore’s guts. See, plenty of plants have defensive trichomes like the horsenettle. Some of them are specifically referred to as hooked trichomes, and can actually capture insects that encounter them.

And for a while, researchers assumed this was a relatively passive process that would occur when insects walked across or bumped into a trichome. But in yet another study from 2017 in the journal  Frontiers in Plant Science, one group showed it can be a bit more… personal. In the paper, they looked at  leafminer flies interacting with plain, boring old kidney bean plants.

And… some flies’ legs did get trapped, which is about what fly part you’d expect to bump into the trichomes first. What the researchers saw most often, however, was that flies became impaled when they extended their mouthparts to feed. And second most often after that?

Well, female flies have an organ called an ovipositor that they use to deposit eggs. And when a female fly went to lay eggs in the presence of a trichome… Well, ouch. These flies remain trapped until they struggle free, and that… That just can’t be comfortable.

Even if they escape, they’re scarred for life. On the list of effective predator defenses, I have to rate this one pretty high. And pretty hardcore.

So there you have it. These are only a few examples of what trichomes can do, which just goes to show that, before we invented “the Rachel,” Mother Nature already came  up with totally killer hair. Thanks to our patrons on Patreon  for supporting this channel.

We couldn’t get to dive into these killer topics without our community of Patreon backers. Plus, our patrons get access  to a whole bunch of perks, like our patron-only Discord server, a monthly exclusive podcast, and even our blooper reels. If that all sounds good to you, head on over to Patreon.com/shishow to learn more.

That’s Patreon.com/scishow. Thanks for watching! [ OUTRO ]