Pleased to meat you by Mark Freeth

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As far as most kids are concerned, the Venus flytrap is the coolest plant in the world. I remember wanting one as a pet(?) when I was little. I would watch on TV as an unsuspecting fly would land in the flytrap’s mouth(?), and it would snap shut locking the fly inside. I always wondered what it would feel like to be bitten(?) by one. Of course, pop culture only increased my curiosity: Super Mario Brothers had monsters that resembled the flytrap poking up out of pipes, and the Venus flytrap in Little Shop of Horrors actually ate people.

Apparently, kids’ fascination with Venus flytraps continues, even today. We are discussing ecology in my 7^th grade science classes, so we were talking about producers and consumers. Of course, they already have a basic background in this topic from 5^th and 6^th grade, so it was just a review for the most part; but, I was surprised at the number of kids who asked the questions, ”Would Venus flytraps be considered producers or consumers, since they are plants, but they eat flys?” and ”Since they eat flies, do they do photosynthesis?”

Sounds to me like another “Kids Want To Know” article is in order!

Dionaea muscipula

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If you’re like me, you probably always imagined that the Venus flytrap was some exotic plant only found deep in the Amazon rainforest or some place similar. I was very surprised to learn that they are actually native to the United States; specifically (very specifically, I might add) the Carolinas. In fact, they only occur at 100 different known sites along a 100 mile strip that spans the wetland pine forests of northern South Carolina and southern North Carolina. It is estimated that only about 150,000 individuals remain in the wild, and that number is declining due to habitat loss. It is listed as vulnerable on the IUCN Red List, and petition has been made to the U.S. Fish & Wildlife Service to add it to their endangered species list. Though it remains unlisted at this time, a few protective actions have been taken. For example, it is illegal to remove them from the wild; so, if you would like to grow one at home, you’ll have to buy it from a nursery.

Producer, Consumer, or Both?

This is the big question that all of the kids ask, and it makes for a good teachable moment. In school, we tend to teach things in a very linear, structured way. There are producers, and there are consumers. They are two separate categories. In reality, very few things in nature fit in one nice, neat compartment. The Venus flytrap is a perfect example. Sure, they are plants made up of plant cells, so they have all of those organelles that you learned about plant cells having back in elementary school - including chloroplast; and, like other plants, they make their own energy through the process of photosynthesis; so, they are producers. However, the flytrap (along with most other carnivorous plants) lives in an environment where the soil contains very little nutrient content. Plants need things like nitrogen and phosphorus to survive. In most environments, they absorb those nutrients from the soil via their root system. Since they weren’t available to the Venus flytrap (or its ancestors), adaptations had to be made, and the work-around that they came up with were nothing short of ingenious.

The actual trap part of a Venus flytrap is made up of a modified leaf sitting atop a petiole. The petiole is the stalk-like portion that attaches the trap to the rest of the plant. The center of the leaf hinges on a small projection called the midrib that connects the trap to the petiole. When the trap is open, each lobe of the leaf is convex, bending outward around the edges and bulging in the center. The outer fringe of each lobe is lined with a series of teeth that interlock when the trap closes. The act as prison bars to capture large insects but allow smaller insects to escape. The leaf is also covered with stiff hair-like structures called trichomes that act as triggers for the trap. When it snaps, it can close in as little as 0.04 seconds! A single plant will usually have anywhere from 4 - 7 traps on it.

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How The Trap Mechanism Works

As I read about how the trap worked on these Venus flytraps, I was absolutely amazed at the mechanism and how efficient the entire process is. The plant is actually quite selective about what it chooses to trap so that not a drop of energy is wasted.

The process begins when an insect is attracted to the sweet smelling nectar and inviting pink coloration on the plant’s leaf. When a fly lands on an open trap, it is very likely to activate one of the trigger hairs. The trigger mechanism causes a release of calcium ions that is detected as an electrical signal. It is actually pretty similar to how action potentials work in the human nervous system. I always imagined that the plant would then react immediately, trapping the insect and devouring it. But, the flytrap is very patient. If you think about, anything could have moved that hair: the wind, a raindrop, debris blowing in the wind. If the trap snapped every time anything touched it, a lot of energy would be wasted closing and then resetting the trap. Instead, the plant starts a 20 second countdown. If another nothing happens within that 20 second window, the plant ignores the signal. However, if another hair is triggered before the countdown ends, the trap closes in the blink of an eye. This happens by hydrostatic pressure. The leaf lobes quickly fill with water causing them to flip from a convex shape to a concave shape. Still, though, the plant doesn’t commit to the kill. It is still analyzing its prey to see just how much effort it will have to put into the job. The bigger the insect, the bigger the struggle; and with each trigger hair that is tripped, the flytrap primes itself a little more by producing a hormone called jasmonate. It tells the gland containing the plant’s digestive enzyme how much it needs to secrete. This way, the Venus flytrap can release an amount proportional to the size of the insect. Nothing goes to waste. The glands don’t even begin producing until after the fifth trigger is detected. This goes on for 6 or 7 hours before the trap closes entirely forming an airtight seal. The insect will suffocate, and all of those digestive juices that the plant has been measuring out will begin to flood in. While not all of enzymes within the digestive cocktail have been identified, they seem to work most efficiently in the acidic environment (pH ~2) created inside of the trap. They don’t digest the entire insect, but instead target the yummy on the inside; leaving behind the chitinous exoskeleton. It usually takes at least a week for the entire insect to be digested, and studies show that the flytrap has a way of knowing precisely when the job is done. It has chemical receptors that can taste the chemicals in the insect’s blood. When it not longer tastes those chemicals, it knows that the process is over, and it cansuck its digestive juices back in to begin absorbing the nutrients like nitrogen and phosphorus from them. Interestingly, it also absorbs the sodium from the insects. Most plants cannot live in a high sodium environment, but the Venus flytrap uses it perhaps as a part of the electrical signaling system activated by the trigger hairs or as a way to control water uptake in its boggy environment.

But, Would It Hurt To Be Bitten By One?

This is always the next question. The quick answer is no. while the trap does close extremely quickly, the teeth are actually quite soft compared to a human finger.

In Conclusion

The Venus flytrap is way cooler than I had ever imagined it to be when I was a kid! Not only can it count, but it has the ability to start its own internal timer. While it does use photosynthesis to make its food and to procure most of its carbon (making it a producer), it has also adapted an ingenious way to digest insects to get the other nutrients that their native soil lacks (making them carnivores, and therefore consumers). It is a perfect example of how science is usually anything but exact, with blurred boundaries between just about every category that we try to group things into and exceptions to almost every rule (note I didn’t say law). After writing this article, I think I will look into getting one to keep in my classroom!

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Sources
UCSB ScienceLine

Venus Flytraps Are Even Creepier Than We Thought by Ed Yong

The International Carnivorous Plant Society

The Venus Fly Trap’s Lethal Allure by Abigail Tucker

IUCN

Comparative kinematical analyses of Venus flytrap (Dionaea muscipula) snap traps by Simon Poppinga et al

Venus Flytrap's Speed Secret Revealed by Robin Lloyd

Facts About Venus Flytraps

Larry Bird Johnson Wildflower Center