[♪ INTRO]
When you hear the term carnivorous plant, your mind might
conjure up a few dramatic images. Like a Venus fly trap snapping
its jaws around its prey, or a small mammal using a pitcher plant as a toilet.
But in the nearly 100 million years carnivorous plants have been on Earth,
they’ve evolved a bunch of different tricks for catching prey.
And some are a lot more subtle than others.
In fact, some plants have developed ways to trap their
unsuspecting prey…underground.
And scientists have found a few types of underground traps that get the job done.
If carnivory works so well above ground,
why might a plant want its traps buried in the soil?
Carnivorous plants of all types tend to live in environments where the soil
can’t provide enough of the nutrients they need, like nitrogen and phosphorus.
So instead, they’ve evolved to get those nutrients from critters.
But critters can serve another important role in a plant’s life.
They can help the plant reproduce.
And you don’t want to accidentally eat your pollinator!
So one advantage of underground traps is that it puts a lot of space between
the structures used for killing, and the structures needed for making babies.
Take Philcoxia, a genus made up of three Brazilian plant species
described back in 2000, living in low-nutrient and shallow sand.
Philcoxia’s underground traps are made from
modified leaves and are pretty unassuming.
They’re tiny…only about a millimeter in size…and produce a sticky goo
that stops microscopic prey dead in its tracks until it’s, well, dead.
Plenty of non-carnivorous plants use adhesive substances as a kind of defense,
so before scientists could call these plants carnivorous, they needed to figure out
if they were actually eating the stuff they catch,
including tiny worms called nematodes.
In order to be considered a carnivorous plant, that plant must trap, kill, digest,
and absorb nutrients from prey, and then use those nutrients to help the plant grow.
So there was a chance Philcoxia was catching microorganisms,
but not actively digesting them.
It’s not carnivory if you just take advantage of that decaying animal body
leaching nutrients into the soil, even though it died after getting stuck on you.
To untangle this mystery, one team of scientists fed nematodes
a diet laced with nitrogen-15, and then fed these worms to their plants.
Compared to most of the nitrogen atoms found in nature,
nitrogen-15 has an extra neutron, which makes it a little bit heavier.
Plants can’t really tell the difference,
so they’ll use it just as readily as they will the standard stuff.
So the team tracked how fast this nitrogen started showing up in Philcoxia’s leaves.
If it happened really quickly, like within a few days,
that would suggest the plant wasn’t waiting around for the nematode corpses
to decay on their own.
They were actively digesting their food.
Since it took less than a day for the leaves to start incorporating the nitrogen,
the evidence suggests Philcoxia really is carnivorous.
Sticky traps like these are referred to as passive traps,
because the plant doesn’t move to trap its prey.
And our next example of underground carnivory:
the African genus Genlisea uses another kind of passive trap.
Their so-called eel traps are long,
thin tubes with an entrance at one end and a digestive chamber at the other.
Small hairs line the inside of each tube, and all point away from the entrance.
That makes it hard for the prey to turn around and go back the way it came.
It would be like trying to push your way through
a narrow tunnel lined with a bunch of swords pointing at you.
The eel traps look just like a small root, so at the microscopic level they can
blend in with the damp surrounding soil and offer
a nice surface for unsuspecting prey to crawl along.
Like Philcoxia, Genlisea plants prey on microscopic animals and bacteria.
But some underground traps can catch larger prey.
In 2022, scientists reported the discovery of a Nepenthes pitcher plant
which can catch insects in its underground pitchers.
This species is found near the top of a dry and windy mountain ridge
on the island of Borneo, and may have evolved underground traps because
the environmental conditions and food supply are more consistent down there.
Now, this species does produce some above-ground pitchers much
higher up on the plant, but most are below ground.
Usually, they take advantage of the empty space created near tree roots,
but occasionally, they move a bunch of soil aside while growing.
That means they have to be made of sturdier stuff so they don’t collapse.
And to provide that extra support, these pitcher plants have to invest even
more energy into growing them…which they have to recover in order to survive.
This suggests there’s quite the food supply down there.
Early research suggests that ants make up most of their diet.
Now a tunneling ant falling over a pitcher’s ledge to its doom may sound pretty
dramatic, but our last example uses an active trap that sucks you in. Literally.
Bladderworts, or Utricularia, are a genus of
over 200 species found across the globe.
They’re named for their bladder-shaped traps,
which are either fully submerged in water or buried in damp soil.
The traps work like a suction bulb, relying on negative pressure.
The plant invests energy to pump water out of the
little bladders and create a vacuum behind the trap door.
When unsuspecting prey brushes against a trigger hair,
the door opens and the prey is sucked right in!
The whole thing happens in just a few milliseconds.
Imagine feeling something brush up against your leg, you blink,
and next thing you know you’re trapped inside a giant stomach.
But the traps aren’t perfect.
Sometimes the sensitive door is triggered by accident,
and the plant will have to spend time and energy resetting itself.
As a silver lining though, that false alarm might suck in nutrients dissolved
in the water, or maybe a wayward microbe that wouldn’t normally trigger the trap,
but has terribly bad timing.
There is one type of trap scientists haven’t seen underground,
the active snap traps like those used by Venus fly traps.
But a new discovery could update this list anytime.
So insects and microbes beware!
If you think you can escape the plants hunting you
by tunneling underground, think again.
And if you, dear viewer, think you can escape this video
before I tell you how awesome you are, think again.
You are awesome!
Just watching this video makes you awesome, at least to us, because it means
you’re thinking about the world complexly and you’re interested in learning stuff.
It also helps us reach more eyeballs and earholes.
So thank you for watching SciShow!
And if you wanna help us reach even more eyeballs and earholes,
you can become a patron at www.patreon.com/SciShow.
Thank you for being awesome!
[♪ OUTRO]