The Pipevine Caterpillar Thrives in a Toxic Love Triangle

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The devilish caterpillars of the pipevine swallowtail butterfly *devour* the California pipevine, never mind that the plant is trying to poison them. Their butterfly moms don’t pollinate the pipevine in return, though. So the vine traps unlucky gnats in its labyrinthine flowers to do the job.

TRANSCRIPT

This is the story of a love triangle between a plant, a striking butterfly and an intrepid – though unlucky – gnat.

Like every good love story … it has plant sex, deceit, and even an attempted poisoning.

At the center of this triangle is the California pipevine. Its supple vines wind around other plants or structures, like this arbor.

It’s also known as the California Dutchman’s pipe because its flowers are curved in the shape of a tobacco pipe.

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And then there’s these “lips.” Oh hello, gorgeous!

The vine grows heart-shaped leaves, but don’t be fooled. The plant produces poisonous compounds that could cause kidney cancer if you ate it.

But the California pipevine swallowtail butterfly loves it, even though the vine is trying to poison the butterfly’s babies. Talk about a toxic relationship!

The caterpillars have evolved to depend on the vine. It’s their only food. And they turn its poison into their own weapon. As they chomp away, they accumulate the toxins in their bodies and make themselves noxious to predators.

The bright orange screams “I can make you sick!”

Even the butterfly’s eggs are crusted with toxins.

After hatching, the caterpillars feast side by side. Scientists call this gregarious behavior. They’re not just being social. Feeding together helps them get bigger faster, though scientists don’t know exactly why.

And the faster they grow, the sooner they’ll stock up on those defensive compounds.

So does the pipevine get anything out of this deal? Pollination by the butterflies, maybe? Nope.

They drink nectar from other flowers.

So when the pipevine’s flowers come out in early spring, they lure in and trap tiny flies called fungus gnats.

The flowers entice them with a mushroomy aroma that reminds the gnats of the fungi they feed on.

Once in there, it’s really hard to get out. Here’s what it looks like inside the flower, from the bottom of the pipe.

This is the actual exit ... the way it got in.

And this is where the flower keeps its pollen. It *could* be a way out, all lit up by the sun. So, the gnat flies up.

It gets stuck, at least for a bit. But the flower doesn’t eat it, like a carnivorous plant would. The flower only needs to keep it hostage until some pollen grains attach to the fly’s hairs. This is called deceptive pollination.

For many gnats the ordeal is too much. They don’t make it out.

But some do escape. If one falls for the same pipevine trick again and gets caught in another flower … boom! Pollination. That flower will turn into a seed-carrying fruit that will eventually lead to new places for this butterfly to lay her eggs.

She’ll never know the debt of gratitude she owes a certain disoriented gnat.

Hi. It’s Laura. Sometimes it literally stinks to be a pollinator. Flies can’t resist the corpse flower. It looks like raw meat and smells like a dead rat. And did you know flies have a secret set of limbs beneath their wings? No? Well, what are you waiting for? Watch the episode! Thanks!