What's really going on inside an insect-munching Venus flytrap
- Venus flytraps mostly catch spiders, ants, and other critters that can’t fly.
- The trap is made of modified leaves containing three trigger hairs and when the hairs are brushed, it sends off an electrical signal.
- That signal sets off a countdown. If the prey escapes in under 30 seconds, nothing else happens. But if it brushes against another hair, the trap slams shut and the Venus flytrap will begin to digest the insect.
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Following is a transcript of the video.
Narrator: When it comes to deadly predators, plants generally don’t come to mind. After all, they’re typically at the bottom of the food chain. But the Carolinas are home to one vicious vegetable: The Venus flytrap.
Using its famous trap, it can catch prey faster than you can blink. But what happens next…inside a Venus flytrap?
Funny thing about Venus flytraps: They don’t usually trap flies. In fact, winged insects only make up 5% of their diet.
Sorenson: We really ought to be calling it the Carolina spider trap. Because it’s only found in a little piece of the Carolinas, and it mostly eats spiders and ants.
Narrator: But regardless of the species, that bug is going to have a bad day. It all starts when the victim wanders into the trap, possibly lured by the bright-red hue or fragrant scent. Or maybe they’re just unlucky.
Sorenson: We think the spiders mostly just blunder.
Narrator: That trap itself looks like an open mouth. It’s made of two pads attached to a hinge.
Sorenson: On each one of those pads there are usually three little trigger hairs in a triangle. And those trigger hairs are very, very sensitive to being disturbed.
Narrator: The first time the spider knocks into a hair, it sets off an electrical signal, sort of like the electrical currents in your brain. That signal starts the countdown.
If the bug escapes within 20 to 30 seconds, nothing else happens. That way, the plant doesn’t waste energy. But if the bug brushes against another hair… SNAP! In just 100 milliseconds — about four times faster than you can blink — the trap slams shut.
Sorenson: The trap rapidly goes from convex to concave on each side, and the long little spikes on the rims of the pads interlock to form kind of a cage.
Narrator: Now, the spider isn’t happy with this turn of events. So, it tries to escape, which is exactly what the plant wants.
The more the spider struggles, the more it knocks into the trigger hairs, the tighter the trap closes. And after an hour or two, the trap locks completely. Cells on the edges of the pads secrete moisture, which glues the edges together to form an airtight seal. Suddenly, that trap isn’t a mouth anymore.
It’s a stomach. Digestive juices flood into the closed compartment, dissolving the spider’s soft organs. And the trap’s lining sucks up that nutrient-rich slushy.
After about a week, all that’s left is an empty husk — the spider’s exoskeleton. Next, the trap opens and the husk tumbles out. The trap’s now ready for its next meal.
But bugs aren’t the only food the trap captures. Just like leaves on other plants, the trap’s surface contains a green pigment that lets it convert the sun’s energy to sugar through a process called photosynthesis. So then, why bother with the bugs?
Well, Venus flytraps live in acidic, waterlogged soil that doesn’t have many nutrients. So instead of slurping up nitrogen and phosphorus through its roots, it needs to borrow some from the bugs. That explains why it shares its home with other hungry carnivorous plants like pitcher plants and sundews.
Which means one thing: North Carolina is not a fun place to be a bug.
EDITOR’S NOTE: This video was originally published in September 2019.
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