Butterfly Does Great Ant Impressions

It's good to be the queen. That's what the Rebel's Large Blue butterfly has discovered. The insect has found a way to imitate the smells and sounds of queen ants so well that worker ants welcome caterpillars into their nests. A group of scientists have just figured out how the butterflies pull off the complex disguise, and their findings are published in today's edition of the journal "Science." Jeremy Thomas, a professor of ecology at Oxford University, talks about the findings.

MADELEINE BRAND, host:

Back now with Day to Day. Let me tell you, it's good to be the queen, even the queen ant. That's what a certain type of butterfly has learned. As caterpillars, they've learned how to masquerade perfectly as ant queens. They trick other ants into treating them like royalty, even killing their own offspring to feed the hungry caterpillars. Just how does this butterfly pull off this evolutionary stunt? Well, Jeremy Thomas and his colleagues have figured it out, and the research appears today in today's edition of the journal Science. Jeremy Thomas is a professor of ecology at the University of Oxford. He joins me now. And ants are extremely protective of their nests, I understand. So, how does a caterpillar manage to work its way inside these nests?

Dr. JEREMY THOMAS (Ecology, University of Oxford): Yes, you're right. Ants will kill almost anything that goes into their nest. But these caterpillars have two tricks. One is that they have chemicals that mimic the chemicals that the ants have. So, they smell the same as the ants, and that allows them to get in, but they also have this further trick. They can produce sounds and they actually imitate the sounds that the queens make. So, the workers are tricked into thinking that these intruders are actually the most important object in the whole society.

BRAND: Well, let's hear some of that sound. Now, this is the queen ant, letting her colony know that she's in charge.

(Soundbite of queen ant sound)

BRAND: OK. And now here is the caterpillar's version.

(Soundbite of Large Blue caterpillar sound)

BRAND: So, it doesn't sound exactly the same, but enough to trick the ants?

Dr. THOMAS: Yes, that's right. And to human ears, they do sound really rather different, but there are certain parts of the sound that are absolutely spot on, absolutely identical. The nearest comparison I can give is two very different musical instruments, something like a violin or a tuba and a trombone, that although the sounds they produce are really rather different, they're playing the same tune, and it's the tune that the ants can recognize, a tune that says I'm a queen ant; treat me like royalty.

(Soundbite of laughter)

BRAND: And then they do, and as I said in the introduction, they actually will feed these caterpillars their own offspring if they demand it?

Dr. THOMAS: They will if conditions get really harsh. If they're starving, they certainly will kill their own young to feed these caterpillars instead.

BRAND: But why would these caterpillars want to invade the ants' nest in the first place? Can't they take care of themselves?

Dr. THOMAS: Well, it's the end of a remarkable long evolutionary process that has probably been going on for millions of years, and they can really be sort of parasites for the ants. In nature, where there is a resource going up for grabs, sooner or later, something seems to evolve to fill that niche.

BRAND: And so, what does this mean for the ants?

Dr. THOMAS: Well, it's very bad news for the ants, as a matter fact. There's no detectable benefit for them at all. It really is an intruder that weakens the whole colony so much that they - often the colony dies, because they get the worker ants working very, very hard to get enough food for them, exhausting its host.

BRAND: Jeremy Thomas is a professor of ecology at the University of Oxford. He coauthored the study on butterfly social parasites. It appears today in the journal Science. Thank you very much.

Dr. THOMAS: Thank you.

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