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How Do Ants Survive Floods? Rafts Of Course


The ant is tiny, but admirable. They have an untiring work ethic and work together in concert and harmony. You suppose any human could learn from that?

Jessica Purcell, an entomologist at the University of California, Riverside, has been studying a species of ant that lives in the floodplains of central and southern Europe and survives by floating out of trouble on rafts on their own extraordinary construction. Jessica Purcell joins us from the university. Thanks very much for being with us.

JESSICA PURCELL: Thank you so much for having me.

SIMON: I can't pronounce the name of the ant. I'm sure you can.

PURCELL: Right. The ant is called Formica selysi.

SIMON: I would've said Formica.

And what do they do about flooding?

PURCELL: Well, they specialize in living in floodplains, which seems like a pretty bad idea for a subterranean insect. But whenever it floods, they're able to actually build rafts out of their bodies and float the safety.

SIMON: Build rafts out of their bodies? How do they do that?

PURCELL: Well, the way that we've looked at it in the lab, they just sort of join together by attaching, tarsus-to-tarsus, so leg-to-leg, or mandible-to-leg, so mouth-to-leg.

SIMON: Who decides you-go-here, I-go-there?

PURCELL: What happens is the workers seem to be sort of the driving force in the assembly of the raft. The queen will sit very still. She'll actually be groomed by the workers in the midst of this emergency, so she's been taken care of. And ultimately, she's sort of lifted up and placed right in the center of the raft under a dome of workers and with a platform of workers below her.

SIMON: Don't the ants on the bottom get an ant mouthful of water?

PURCELL: We thought so originally. And actually, we decided to study this behavior because we were interested in the role of altruism, so self-sacrifice, in this cooperative society. And it turns out that the ants can be submerged for hours and actually survive. So we see very, very little mortality - almost no mortality in these rafts. And, in fact, they put the youngest members of the society, the brood - the larvae and pupae - on the base of the raft, and those guys survive, too.

SIMON: Do they show signs of having a memory from one flood to the next?

PURCELL: We do need to do more research to understand the mechanisms of this sort of group memory. But there is a very clear pattern that emerges when we repeatedly expose ants to similar conditions. And they very much respond based on their prior experience.

SIMON: Are we talking about brainpower here - intelligence?

PURCELL: Well, I think it's a very different kind of intelligence than what we're used to thinking about. So an individual ant is not overly intelligent. It's able to follow signals from - you know, chemical communication signals from other ants. But by working together and through differentiation and specialization on different tasks, they can achieve these pretty marvelous social outcomes. So there's more of a swarm intelligence, I would say, than sort of an individual intelligence.

SIMON: You know, we speak of armies of ants. It strikes me what you (laughter) - what you have here is an ant navy.

PURCELL: Yeah. That's a really good analogy, actually. So the ants that I study are native to the Alps. They're pretty mild. They're not very aggressive. And the other species of ant that has been studied in terms of rafting behavior is actually a more fierce naval formation, if you like, because they're the invasive fire ants that actually sting.

SIMON: Pirate ants.

PURCELL: That's right. Exactly.

SIMON: Jessica Purcell is an entomologist at the University California, Riverside. Thanks very much, and good ant-watching to you.

PURCELL: Thank you very much.

(SOUNDBITE OF SONG, "ANTS GO MARCHING") Transcript provided by NPR, Copyright NPR.

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