Would you raise the baby that ate your siblings? - Francesca Barbero

You might not guess it, but this Alcon blue butterfly

is a parasite whose offspring will live highly unusual lives.

She lays pinhead-sized eggs on a wildflower and is off.

The first tiny caterpillar hatches a few days later.

After two weeks living within a flower bud,

he embarks on a high-risk operation that will require infiltrating

a densely guarded fortress undercover.

He secretes a thread of silk and descends to the ground.

Here, he's more vulnerable than ever, but he holds still and waits.

His descent perfectly coincides with the peak foraging hours

of the nearby red ant colony.

Soon enough, a worker ant encounters the caterpillar.

She inspects his cuticle with her sensitive antennae

and picks up on key chemical cues that she uses to recognize her kin.

This is all part of the caterpillar's disguise.

The worker picks him up and reverses course.

Indeed, the caterpillar doesn't battle his way into the fortress.

No— he wouldn't stand a chance.

He's shepherded in because the ant

is treating him like one of her colony's own larvae.

They pass legions of ants poised to attack invaders

and enter the intricately architected, subterranean nest,

which is sheltered, moist, and stockpiled with resources.

If the caterpillar's mimicry didn't work,

he might have been left for dead or taken as food himself.

Instead, the ant places the caterpillar in the nursery,

among the colony's own cherished brood.

Here, he produces sugary secretions that the worker ants feed from.

The nurse ants dote upon him,

regurgitating food into his mouth frequently.

But he has a voracious appetite.

He arches his body in a begging posture to obtain more food,

and, every now and then, eats one of his own nestmates.

The caterpillar also does things that the ant larvae can't:

he makes noises that sound a lot like those emitted by the ant queens.

In effect, he signals that he's royalty and should be prioritized

over the actual ant larvae.

And that's exactly what happens.

The nurse ants feed him extra.

And when a wild boar causes part of the nest to collapse,

the ants rescue the caterpillar first.

While members of the ant colony suffer reduced survival rates

because of the burdensome caterpillar,

he passes the harsh winter living like royalty.

Come June, he's stored up plenty of nutrients

to make a dramatic transformation.

He forms his chrysalis, and for three weeks,

he uses a tooth-and-comb organ to create more queen-like acoustic vibrations,

attracting workers to clean him.

Then, at dawn one day, he emerges an adult butterfly.

Wings still wet, his body easily fits through the gallery opening,

and finally, 11 months after being taken in,

he basks in the sun and begins searching for a mate.

When he dies about a week later,

he'll have spent the vast majority of his life in the realm of the ants.

The Alcon blue is one of as many as 200 parasitic butterfly species,

all of which target ants.

Sometimes, multiple caterpillars inhabit the same ant colony at once.

Some stay for almost two years.

But researchers are still parsing these complex relationships.

For instance, certain ants guard Japanese oakblue caterpillars from predators

and consume the sugary secretions the caterpillars produce in return.

But it turns out that this sweet concoction

isn't a simple form of mutual assistance.

Instead, chemicals in the secretions actually manipulate the ants' behavior,

inhibiting their movement

and making them more protective and aggressive caterpillar guards.

Despite these masterful manipulations,

parasitic butterflies are vulnerable themselves.

They're also the targets of parasitism.

Even within their adopted, high-security hideaways,

parasitoid wasps sometimes track the caterpillars down

and lay eggs on their bodies.

When the wasp larvae hatch, they consume the caterpillars alive.

And because their life cycles consist of such a complex choreography

involving specific plants and ants,

small environmental changes can affect their populations.

One parasitic butterfly species actually went extinct in the UK in 1979,

before being reintroduced a few years later.

They've since rebounded alongside efforts to restore the meadow habitats

their host ants require to thrive—

helping preserve these riveting relationships

and the astonishing adaptations they inspire.