The life cycle of the butterfly - Franziska Bauer

In order to become a butterfly,

a caterpillar’s body dissolves almost completely

and is rebuilt from its own juices.

As inconvenient and even downright dangerous as this process sounds,

it’s actually quite common.

Butterflies are just a few of the 800,000 insect species

that transition from larvae to adults through complete metamorphosis.

That’s approximately 85% of insects and 70% of all known animal species.

But how exactly does a caterpillar become a butterfly?

When a caterpillar hatches from an egg,

it has none of a butterfly’s physical traits.

It does have groups of cells inside its body called imaginal discs

that will eventually become its butterfly parts.

For now, these cells remain dormant.

Juvenile hormone suppresses their activity,

and prevents the caterpillar from beginning metamorphosis too early.

Immediately after hatching, the caterpillar begins to feed,

building up fat until its rigid skin, called a cuticle, becomes too tight.

At this point, a hormone called ecdysone triggers the cuticle to shed, or molt.

As the caterpillar grows, it usually molts four times.

Then, when it’s nice and plump,

the caterpillar’s levels of juvenile hormone drop,

which triggers it to stop eating and moving.

A final burst of ecdysone

prompts the caterpillar’s cells to begin to self-destruct.

Soon, the muscles, fat, and other tissues are almost entirely liquefied,

though the imaginal discs stay intact and begin to grow.

At the same time, a second skin layer called the pupal cuticle

forms underneath the first.

One more molt exposes the hard exterior of the pupa.

Besides the imaginal discs, only a few tissues are spared,

including parts of the respiratory system,

the heart,

some abdominal muscles,

and the mushroom bodies of the brain.

The caterpillar juice then fuels the development of the imaginal discs

into eyes,

antennae,

legs,

wings,

genitalia,

and other body parts.

Once its new body is built, the insect molts one last time,

shedding the pupal cuticle.

From there, it’s free to fly away a new butterfly.

Even after such a dramatic transformation,

the butterfly does retain some memories from its caterpillar days.

It’s likely the mushroom bodies of the brain

carry important knowledge from the caterpillar over to the adult butterfly.

How did such an involved developmental process come to be?

We don’t know for sure.

The leading theory is that the caterpillar is actually a drawn-out version

of a life stage that takes place inside the egg for some other insects.

According to this hypothesis, over millions of years,

the larvae evolved the ability to eat and live outside the egg.

Regardless of how complete metamorphosis originated,

it’s become part of the life cycles of a dizzying number of insect species.

Still, plenty of species get along perfectly well

with a simpler developmental process.

What survival advantages might complete metamorphosis provide

to make up for the added hassle?

For one, it keeps larvae and adults

from competing for the same habitats and food sources.

And while the pupa may seem vulnerable,

this immobile stage can actually be a good way

to pass parts of the year when food is scarce.

To us, a butterfly’s metamorphosis might sound as fantastic

as a phoenix rising from its ashes.

But these transformations are taking place all around us, all the time.

From the Hercules beetle

to the honey bee

to the garden ant,

countless squishy larvae dissolve and emerge

as armored, aerodynamic, and nimble adults.