How Do Worms Turn Garbage into Compost?


Everyone’s gotta eat. Carnivores like a meaty burger. Herbivores are salad fiends. 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 as “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 Slimey 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. Before we get to the chemistry, some biology
and physics. Earthworms are part of a superfamily 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. Up front 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 worm’s
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 earthworm’s intestine receives 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 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. Lipase 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-y 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 Slimey! 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 worms’ guts, we here
at Reactions call this chemically processed, calcium injected, black stuff, mana. So here’s why worm poop is big deal. Earthworms munch up indigestible garbage and
cast out soils that can support healthy ecosystems: Earthworms break down all that cellulose that
could clutter up, then choke out forests. A herd of earthworms can munch over 20 tons
of dead organic matter per acre per year: all around the world there are examples 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. Let us know in the comments what creature
chemistry you’d like to hear more about. Slimey hagfish? Poison dart frogs? Blue blooded horseshoe crab? Nature is weird. Anyway, thanks for watching, and thumbs up
on the way out.

24 thoughts on “How Do Worms Turn Garbage into Compost?

  1. I don't know what kind of research y'all could do on this, but there is a caterpillar known as the Marius Hairstreaks that turns the color of the flowers it eats. I'd love to know how on earth the chemistry of that works!

  2. You start talking about what comes out of earthworms, but then just say that the poop is called castings, and doesn't say anything about what it actually contains.

  3. would be cool if you could do something on nature's toxins. be it snake venom or nicotine. I think pretty much anything can be interesting

  4. you didn't mention that the worms are also eating the juicy microbes that are also decomposing plant debris…worms don't do it all by themselves

  5. Do the worms crawl into your compost bin? or does the "science" of composing create worms.. like dead meat can creat maggots…

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