- Hey, smart people, Joe here. Here's what your preschool teacher probably taught you about
how butterflies are made. Cute little caterpillar
just eats and eats and eats, and gets all fat, and
then it eats some more, and then it builds itself a sleeping bag, crawls in, and something happens. And voila, a butterfly pops out. Well, I'm here to tell
you that it's a lie. In fact, no book has done more to mislead the world's young people
about the biological marvel known as metamorphosis than this one. That might be a little bit extreme. What actually happens
when a caterpillar morphs into a winged marvelous
adult is so flippin' cool, some of nature's most
remarkable biological processes and all of that mind blowing stuff happens in this part that
the book just skips over. The transformation is less
"Very Hungry Caterpillar" and more "Gremlins." Unlike humans, who come outta the womb looking like little, squishy
versions of our adult selves, caterpillars transform their entire bodies into something completely different with entirely new body parts. They basically live one life, but as two completely different animals. Today, I'm gonna unlock the secrets of what actually happens inside
this little sack of magic. All with the goal of
answering one question. Why do butterflies and other insects actually do this metamorphosis thing? What's it really for? So forget everything you thought you knew about how a caterpillar to
butterfly pipeline works. It turns out the truth is so much weirder. (mysterious music) When I was a kid in elementary school, we raised butterflies in science class. Maybe you did it too. And maybe you're like some people and you did it again as an adult. It's me. Hi, I'm some people. It's me. I still play with
caterpillars, but I digress. Back then you probably watched
a squirmy, little caterpillar wrap itself up in whatever this is. Then a whole different
flippin' thing comes out complete with wings and legs. How'd that happen? If we wanna uncover the real
truth about metamorphosis, there's no better place
to start than with Tim. Tim's in charge of the
thousands of butterflies at the California Academy of Sciences butterfly rainforest exhibit. - The process of
metamorphosis for a butterfly is pretty fascinating and they grow through
four different stages. Egg first, and then a larval stage where they're feeding on the foliage. And then they really go through what some people call
that black box period. They are pupating into a chrysalis, and that's where a lot
of changes really happen before they enter the adult
stage as an adult butterfly. - This process where an
animal completely changes from one form into another
is called holometabolism. Going through this type
of complete metamorphosis is surprisingly common. About 8 in 10 insects,
including beetles, flies, bees, and ants live and grow this way. Butterflies just get all the attention because this is much cuter than this. But those groups of insects
are vast and numerous, which means that about 60%
of all earth's animal species use holometabolism and live
different phases of life as completely different forms, which means this real-life
Pokemon evolution must be a pretty useful way to live. Like Pokemon, the magic
starts with an egg. So a mommy and daddy butterfly meet, like what happens- - So butterflies will mate end to end. So you might see their abdomens connected, but that is what it looks like when butterflies are copulating. And the male will transfer a
spermatophore to the female, essentially, a packet of sperm. She'll hold onto that. - [Joe] So she's holding onto sperm, and then when she lays that egg does the fertilization not happen until like the moment
she's about to lay the egg? - [Tim] Pretty much, yeah. The caterpillar doesn't really
start forming or developing until that egg is laid, and then the clock really starts ticking. - Most female butterflies lay eggs on very specific host plants, since nearly all caterpillars
eat plant matter. I said nearly all, because a
few have been known to dabble in the occasional side of cannibalism. Yeah, Eric Carle didn't
mention that part, did he? Anyway, female butterflies
choose the ideal leafy nurseries based on leaf color, plant shape, or by tasting leaves with their legs. Can you imagine a human mom choosing a baby crib at Target that way? The things we call caterpillars
are butterfly larvae, the second stage of this strange life. All caterpillars come out of the egg equipped with all the genetic programming and cellular building
blocks that they'll need to morph into butterflies later. These building blocks come in
the form of imaginal discs. Basically little seeds made of cells that'll eventually grow
into adult butterfly parts like antenna, eyes, and wings. But that happens later. Right now, caterpillars
are basically stomachs with mouths on a mission to get chonky. - Their primary goal as a larva is to consume and acquire
as many calories as they can to really fuel their
process of metamorphosis. - During this chow down phase of life, caterpillars can grow up to
100 times their original size. For example, monarch
butterfly caterpillars can fit on a pencil
eraser when they hatch. But in a matter of weeks, they'll get more than five times longer and nearly a 1,000 times heavier, sometimes eating more
than 100 leaves a day. But caterpillars are
doing more than eating, and pooping, during this life stage. They're starting the next stage
of their metamorphosis now. As caterpillars grow,
they shed their skin, or molt, multiple times. Each time they look
just a little different on the outside and on the inside. And this, this is where we bust the biggest butterfly myth of all. I feel like when I was a
kid, I was just taught that, you know, they just
like liquefy their body and then a butterfly magically emerges from that soup or whatever. - Yeah, it's kind of like
a tale as old as time. - Look, if you think about it
even for like five seconds, bug soup turning into a butterfly isn't even biologically realistic. I mean, how would that actually work? But this gooey myth overlooks what I think is the absolute coolest
fact about metamorphosis. A while back when I visited
butterfly researcher Arnaud Martin, he made a small incision in the side of the caterpillar
and pulled out this. That is, that's a larval wing. - [Arnaud] That's a baby wing, here we go. - The future adult wing of the butterfly already growing inside the caterpillar. As they grow, caterpillars
develop wing buds, like internal proto-wings
that will one day grow into the full-size thing. These proto-wings, along
with many other proto-organs like eyes and reproductive business, are already partially there in the larva. They're just waiting
for one special signal that tells them when to grow. Once caterpillars finish
their second to last molt before chrysalisification, their bodies release a big
dose of a growth hormone that tells 'em to stop eating
and look for a good place to hang out, literally, for a few weeks. This stage is basically butterfly puberty and it's pretty awkward for them too. Once the caterpillar
finds the perfect spot, it secretes a little dab of silk. Yeah, spiders aren't the only
ones who make that stuff. And it hangs itself from it. - [Tim] So at that stage,
instead of having a new skin underneath it that looks
like a caterpillar, the next skin is really
the cuticle made of chitin of that chrysalis stage. And it's a really cool
transition because you can see a lot of the outlines
of the future butterfly on that pupil case. - [Joe] It just hit me like,
butterflies are like onions, they just keep layers inside.
- [Tim] Yeah, one layer time. - So yeah, a chrysalis is
not a silk sleeping bag that they spin and then crawl into. It's their skin. They take off their
old skin like a jacket, and their new body is inside. This isn't kids book stuff this is more like "Silence of the Lambs." So now we're on metamorphosis stage three, where the caterpillar is now a pupa. Thanks to all the energy and protein stored up during the larva phase, the pupa is physiologically
self-sufficient and lives off the nutrients
it consumed as a caterpillar. And if you thought the run up
to the pupa stage was weird, just wait, things get even
stranger and cooler from here. So if the caterpillar doesn't
like completely dissolve, turn into butterfly soup, then abracadabra it's way into a new body, what is happening inside
that bag of mystery? For starters, a whole lot of dying. See the cells that a caterpillar
doesn't need anymore, they self-destruct. (bomb exploding) This cell death is also
triggered by hormones. Those hormones tell cells to
activate digestive enzymes to break apart the cell's
proteins and other parts, and the pupa recycles this protein to fuel the rest of metamorphosis. So, yeah, pupae
essentially eat themselves. A caterpillar's muscles,
jaws, most of its gut, and stubby little legs,
they all break down because an adult butterfly
doesn't need them. And while things are reorganizing and growing inside the chrysalis, the new parts the future
butterfly will need are already there on those imaginal discs, growing into their final form. For a long time, we couldn't
see what was going on inside of a chrysalis. But with modern technology like CT scans, we can watch the science happen. This is the inside of a chrysalis. And you can see that at the beginning, not a lot going on. You can see the digestive
tract in the middle, and the caterpillar's breathing tubes. You can even see the proto-wings. But none of this really
looks like a butterfly, yet. But over time, the butterfly's eyes get bigger and more
complex, it grows antenna, its body shape changes, and of course, those proto wings-grow into
their full, flappy splendor. Now that the caterpillar is done becoming a completely new animal, the adult butterfly is ready
to emerge from the chrysalis. And this part of the process
is known as eclosion. It starts when the butterflies' brain releases yet another hormone
that gives it the strength to bust through the chrysalis
wall like the Kool-Aid Man. - [Kool-Aid Man] Oh yeah! - And once the butterfly's free, it hangs upside down, pushes
a blood-like substance through its wings to help them expand. This finally allows the wings
to dry and harden enough so the butterfly can
take its first flight. One of the coolest things about this total metamorphosis process is that different families of insects put their own spin on it. Sometimes literally. For instance, instead
of hardening their skin into a protective chrysalis, moths do spin their metamorphic
sleeping sack out of silk. That's probably why they come
out with such great hair. Ants do all this inside enormous colonies pampered by thousands of older sisters. And baby bees do their change locked inside tiny hexagonal prison cells like some weird dystopian
metamorphic "Matrix." Beetles and cicadas do it too, often buried in the ground
for their entire childhood. And if you're a fly, you might do all this in a dead body or a hunk of poo. Where's the children's
book about that, huh? So that's the how. The deeply strange ways insects transform their squishy little larval
bodies into their final forms. But why do they do it? Why is living your life
as multiple life forms such a great recipe for
evolutionary success? Well, I know y'all hate this answer, but we're still not entirely sure why. Sorry, that's science. But here's some theories. Some scientists think that so many insects are fabulously homometabolous
because it means that adults and their young don't compete for food. For instance, while
caterpillars eat leaves and sometimes each other, butterflies drink nectar,
even sweat, urine, or blood. Some adult moths don't even eat as adults since they aren't born with mouths, which is the most extreme way
to avoid food competition, and another tally in the
"Silence of the Lambs" column. Scientists also theorize
that metamorphosis might be a result of adaptive decoupling. This lets adult and juvenile traits evolve independently from each other, since caterpillars and butterflies face totally different
pressures for natural selection. Whatever the reason, and
there may be more than one, the fact that complete metamorphosis is so strikingly common
in the animal kingdom means that this is a hugely
successful way to live in the eyes of evolution. And it's my favorite reminder that even seemingly straightforward
scientific processes that we can see happen
right before our eyes are far more complex and wondrous than we could possibly imagine. So sorry, "Very Hungry Caterpillar," better luck next time. (glass shattering)
(cat yowling) Stay curious. Hi, welcome to "Overcomplicating Things." taking down your childhood favorites here on "Be Smart," okay. How'd that happen? I'm under a lot of
pressure, so okay, sorry.
