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Carnivorous plants exist all around the world. Mayra from education talks about where Venus fly traps are found (surprise, it's North and South Carolina), why they evolved the ability to digest bugs, how they do that, and yes, what happens when you stick your finger in one (not much)! This Pulsar podcast is brought to you by #MOSatHome. We ask questions submitted by listeners, so if you have a question you'd like us to ask an expert, send it to us at firstname.lastname@example.org.
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ERIC: So I've wanted to do this episode for a while because it's one of my favorite unexpected surprises here at the museum. You teach a program about carnivores, you bring out a snake and talk about its adaptations. And then you put it away and take out a tiny little plant, but it's also a carnivore. So what does it eat?
MAYRA: That's a great question. And yeah, it's one of my favorite surprises. Because everybody is expecting another carnivore, we get questions like, oh, it might be a tiger, or it might be something big. And I bring out this little plant and everybody's like, that's a carnivore, but yes, it very much is, and it eats insects. But other carnivorous plants can even eat slightly bigger things that aren't just insects and bugs.
ERIC: So the Venus flytrap is not alone. There's lots of different kinds and even different forms of carnivorous plants.
MAYRA: There are so many different species of carnivorous plants. And there are different kinds of carnivorous plants. So the Venus flytrap is not alone. But it is probably the most famous one.
ERIC: And they are carnivores for the same reason that animals are, they're just obtaining the materials they need to survive.
MAYRA: Exactly, only slightly different. We humans and other animals eat other animals for energy. But Venus flytraps, similar to most plants, can actually photosynthesize. They don't need insects for energy. Instead, they need insects for nutrients.
ERIC: So that's things that you normally find in the soil that plants kind of absorb and then use in their structure. But they get them through bugs instead of the soil in some cases.
MAYRA: Exactly. So most plants usually find nutrients in the soil, that's phosphorus, that's nitrogen, things that they need to grow. But Venus flytraps and other carnivorous plants are usually found in soil that doesn't have those nutrients they need. So they had to develop a different way to get those nutrients. And insects were the way that they developed it.
ERIC: Yeah, so the location of where you find them. You mentioned the soil that doesn't have the nutrients. It was the most fascinating part the first time I watched the program, because in my mind, I'm thinking carnivorous plants, deep in the remote jungles, far, far away from the United States. And the Venus flytrap is only found in...
MAYRA: ...the United States. Yeah, it is found in swampy areas where the soil isn't great. So that is one of the criteria. But it is found in the United States. It is found in North and South Carolina. I was also surprised by that because I thought that Venus flytraps would be tropical, or they would at least not be from here.
ERIC: Yeah, it was super surprising. It was kind of unbelievable that it was like yeah, you can find them in North Carolina, like, okay, that's not what I expected at all. So can you talk about how it works, how could a plant possibly know that a bug has landed on it, because it has that like closing trap. But it doesn't have eyes, plants don't have a sense of touch the same way we do. So what causes it to snap shut and start digesting that bug?
MAYRA: Yeah, so they don't have a brain unfortunately, as cool as that would be. So instead, they have what we call trigger hairs. And basically when the plant is open, it has three little trigger hairs inside of the trap on each side. When something touches it, then an electric pulse goes through there, making the trap close. Except not really, at least not the first time. That's not enough to make that electric pulse strong enough to close. So it needs at least two or more touches within about 30 seconds for it to fully close.
ERIC: So it's really trying to make sure there's actually a bug, that doesn't want to close on a false alarm because that would take a long time to open back up, too much energy expended, something like that.
MAYRA: Exactly. And the more that bug or whatever's in there struggles, the more those trigger hairs are touched, the faster it'll close. So more of those electric pulses will cause that trap to close faster and tighter. Which is important because that trap needs to close air tight before it can start digesting anything.
ERIC: So then after it's closed, the digestion, what happens there? Is it similar to like, digestion like we're familiar with, like acids in our stomach?
MAYRA: Kind of. So it releases what we call digestive juices. So it's not as strong as our stomach acid, it doesn't need to dissolve things as strong as we would eat. But it is strong enough to be able to dissolve the insides of most insects. What I find super cool is that it actually cannot dissolve the outer exoskeleton of most insects. So once it opens up again, after about two weeks or so, you still have the exoskeleton of its last meal just waiting there for you.
ERIC: So it doesn't need to eat that often. If you can call it eating, it doesn't need to catch an insect, that often, if it takes two or three weeks to digest just one, it's not like eating one and then waiting for the next one to come along right away. It's kind of a long process, but it just needs that little bit of extra nutrient from the insects that it can't get out of the soil.
MAYRA: Exactly, it only needs to eat every so often, definitely not as often as we would eat. And it also has a lot of traps per plant. And not all of them need to eat, and not all of them need to eat at the same time. So eventually it'll catch something, especially in the wild, where it's not being fed, it just has to catch whatever happens to come along. Hopefully one of them will catch it. And that will sustain it for a while until another one can catch another insect.
ERIC: It's kind of an awesome example of evolution doing something to solve a problem in a wacky way that's completely different from everything else around it, you know, like, one plant that can start to absorb nutrients in another way starts to, over many generations, turn into a plant that has this, it looks like a mouth, it's got like the spikes on the end of it that kind of look like teeth and the bug lands on it and digested. It's unbelievable that evolution could result in that.
MAYRA: Yeah, it looks so much like a mouth that we expect it to act like an animal or act like a mouth. And it kind of does in some ways, but not the ways that we would expect. And what I find super interesting is that carnivory in plants evolved several times. So these plants aren't necessarily all related to each other. They all just found, like you said, that same solution to the problem.
ERIC: Yeah, it's just the conditions of one specific place. I mean, in North and South Carolina, that one little area has just the different soil composition that led to some plants eventually evolving the ability to get nutrients from somewhere else. And that somewhere else happened to be by absorbing bugs. And the one other thing you mentioned in the show is they still need to reproduce by flowers. And that involves insects coming, landing on the flowers, bringing pollen to other Venus flytraps. And that's kind of a problem, because you don't want to eat the bugs that are going to do that for you. Can you talk a little bit about how those insects stay safe from the parts that actually digest?
MAYRA: Yeah, so a lot of people tend to think that the Venus flytrap, the traps themselves are flowers, but they're actually modified leaves. They just look very flowery to us because they're red and beautiful. But it does grow its own flower. And the really cool thing is that flower will be about a foot or more higher than the rest of the plant, which is very important, because a lot of those insects that are pollinators, like butterflies and bees, tend to be flying insects, so they'll fly from flower to flower. But the Venus flytrap, despite being called a fly trap, doesn't actually eat flies for the most part. In fact, about 80 to 90% of what it would eat are spiders and ants. Those are things that are crawling on the ground and get stuck in those traps. So if you've ever looked at one, the traps are really really low to the ground. But that flower gets really high.
ERIC: Yeah, you definitely have to elevate that to separate your two goals. You want to attract two kinds of bugs, one to absorb and one to help you carry on your genes. When we picture carnivorous plants, sometimes we picture something that's big enough to fit a squirrel, or maybe even a person inside. How big are the leaves on a venus flytrap that trap something?
MAYRA: So the traps on a Venus flytrap tend to be a few inches, max. They're pretty small.
ERIC: Alright, so our big question for today, we get this every time that I've seen the program, some students ask: what happens if you stick your finger in a Venus flytrap?
MAYRA: Everybody wants to know and I wanted to know the exact same thing so I had to look it up and watch some videos. And it turns out that if you stick your finger into a trap, nothing's really going to happen. If you move your finger around a little bit to trigger those trigger hairs then the trap will start to close. But the thing is that the trap needs to close airtight before it starts sending out digestive juices and if your finger's there, that's not gonna happen. However, if you happen to get some of those digestive juices on your finger somehow, well still not much is going to happen except maybe you'll get a blister at the most. Remember, these plants have a hard time digesting even the exoskeleton of an insect, so they're really not going to do much to skin, much less bone.
ERIC: Myra, thanks so much for telling us about Venus flytraps.
MAYRA: Thanks for having me, Eric.
ERIC: You can see video of our Venus flytraps being fed in our Sparks of Science video series, part of MOS at Home, or you can meet them in person at our Garden Walk and Insect Zoo in our Blue Wing. Until next time, keep asking questions.
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