After a caterpillar goes into its chrysalis, you would expect a beautiful butterfly to emerge. But when this parasitoid attacks, the results are very different.

Monarchs eat milkweed — and that makes them toxic to most predators. But biologist Carl Stenoien discovered one parasitoid that is immune to milkweed’s effects. Listen to hear his story.

Brains On! is an award-winning audio show for kids and families from American Public Media.