Season 4 Episode 10 | 4m 49s | Video has closed captioning.
How is it that these detritivores – literally dirt eaters – turn what humans find inedible into beloved compost? After the biology and physics of swallowing and “chewing”, like us it’s all chemistry for digestion. But earthworms have an extra enzyme that allows them to munch through cellulose, the ultimate fiber of that makes tree bark a non-starter in human diets.
Aired: 04/19/17
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(musical chord) - [Narrator] Everyone's gotta eat.
Carnivores like a meaty burger, herbivores are salad philes.
But do you know who really takes the cake?
If by cake, you mean a grimy meal of dirty, nutrient rich, dead leaves and other forest litter?
Detritivores, literally, trash eaters.
Well, for today's video, what you think of is Earthworms, but these little subterranean monsters appetites give us the bountiful world that allows us to farm food for our hungry, omnivorous bellies.
The question is, how does slimy turn dead plants, decomposing animal bits, weird fungi, and even mold and manure into beloved compost?
Let's take a chemical digestion journey, a straight shot from mouth to anus through a munching earthworm's gut.
(upbeat music) Before we get to the chemistry, some biology and physics.
Earthworms are part of a super family of invertebrates called, Megadriles, that have fascinated for centuries.
Charles Darwin himself, wrote his last book on the creatures.
As we said, worms process food in a straight shot.
Their guts don't twist and turn like ours.
Upfront is a toothless mouth, then a series of muscles that suck Detritus in.
Just after the earthworm mouth is a curious set of glands that secrete a milky liquid containing Calcium Carbonate, the same stuff that makes up seashells.
The dirt where worms make their home has a lot of CO2 in it which can mess up a worms body chemistry, making its blood more acidic.
So this gland is a nifty way for worms to balance out their CO2 with soil calcium, which, by the way, means less CO2 makes it into the atmosphere.
Earthworms have a Gizzard too, where churning muscles crush the incoming food, thanks to bits of sand and rock, the earthworm has hoovered up.
Hey, you do what you can if you don't have teeth, but eat all kinds of crunchy stuff.
So the earthworms intestine receive some crushed dirt including plant bits like dead leaves and bark that no human could hope to digest.
For us, a happy human gut is one that regularly has a bit of fiber pass on through, but earthworms eat almost entirely fiber.
So how do they get any nutrients?
Enter a quartet of enzymes, Amylase, Lipase, Pepsin, and Cellulase.
These specialized proteins chop up and modify swallowed food into molecules the body can take in.
We humans, have three of these enzymes.
Amylase in our saliva breaks down starches.
Worms just happen to keep their spit in their guts.
Lipases breaks down fats, so earthworms can digest plant oils.
Then Pepsin breaks down proteins to digest animal bits.
But earthworms can make a dinner of all that vegetable fiber, thanks to Cellulase.
As its name suggests, this enzyme breaks down Cellulose, the hard fiber that gives leaves structure, and lets trees stand tall with wood and bark.
Given enough time, no dead tree is a match for slimy.
All forest litter is not a tasty dirt sandwich, however.
Many plants contain toxins that defend them from hungry creatures.
Polyphenols contain a class of toxic molecules that cause illness or death to insects.
But earthworms, who can't avoid munching polyphenols up, have molecules in their gut called Drilodefensins.
It seems only soil dwelling Megadriles contain Drilodefensins, which is why they can chew right through those dead plants.
A few enzymes aren't the only digestive trait we share with earthworms.
We both have gut bacteria showing just how tiny microbes are.
Not surprisingly, gut microbes in earthworms are soil bacteria that chew nitrogen out of the plant material taking in nitrates and nitrites and expelling nitrogen gas in a process called, Denitrification, which leads us to consider what comes out in the end of the earthworm.
Biologists call earthworm poop, castings.
Given what happens in worm's guts, we here at Reaction, call this chemically processed, calcium injected, black stuff, mono.
So, here's why worm poop is a big deal.
Earthworms munch up indigestible garbage and cast out soils that can support healthy ecosystems.
Earthworms breakdown all that Cellulose that could clutter up, then choke out forests.
A herd of earth worms can munch over 20 tons of dead organic matter per acre per year.
All around the world, there are examples of where they've transformed bad grazing land into bountiful fields.
This is why composters love earthworms.
They're like earth's little garbage people.
Thanks, little guys.
Of course, it's worth saying that there are invasive earthworms disrupting ecosystems in some places.
It's not all sunshine and ponies in the earthworm world.
The nitrogen returns to the atmosphere, eventually completing the nitrogen cycle.
So other plants can mine that vital element anew and make food for organisms like us.
And all those worms drill little tunnels through the soil to let air and water get deeper to feed strong roots of plants and trees.
So, thank you, little garbage people, earthworms.
Your poop is really valuable!
