Locusts weren’t just our ancestors’ problem; they still impact the livelihood of 1 in 10 human beings. The discovery that their “swarms” are actually cannibalistic melees may offer a solution.

Question: Are there species that are more individualistic than humans?

Iain Couzin: Yeah, I mean, there are, I mean, group living isn't, I mean, it's very, very common, but it's not, you know, the only way in which to live. And in fact, we've been studying some fascinating organisms that actually flip between a solitary existence and an incredibly strong collective existence. So one example are locusts. Now, locusts are sort of well known as being sort of biblical plague and so forth. But they're still a real plague. They can actually cover or invade up to one-fifth of the earth's land surface during plague years, which is astonishing. And the Food and Agricultural Organization of the United Nations estimates that the impact to livelihood of 1 in 10 people on this planet to the impact on agriculture and so on. But of course, if you look at the range over which these huge hoards sweep, it's across Sub-Saharan Africa into Asia. And so there's not much financial incentive to do research in this area, but there's, of course, a big humanitarian incentive and it's also a fascinating problem.

And so what locusts actually do is, when times are good, they will avoid each other. They're shy, they're green, they're cryptic grasshoppers, they can't stand being near each other. It's only when times get hard, and the physical sort of contact or the sights and smells of others, causes them to change. And they literally change their color, they become sort of black and yellow with red eyes, and they start marching together, they start swarming together across the landscape. And this is before they get wings, you know, when they're adults, they can then fly together, which disperses them even further.

And so collaboratives of mine at University of Oxford and now at Sydney University, discovered this behavioral switch and so what we were fascinated by was, you know, why are they all swarming together? Why are their kilometers-long locusts all marching in unison, it looks like a cooperative behavior. But what we discovered, is in actual fact, it's driven by cannibalism. When times get hard, they're resorting to eating each other. They run short of protein and salt and water and they start to eat each other. And so the optimal strategy seems to be to try to eat those ahead of you, but try to avoid being eaten by those coming from behind and the outcome is everyone starts to move together collectively. And of course, in that way they can also benefit by saturating predators, they can also benefit by potentially finding new areas of resource. But we discovered that cannibalism is actually critical here. So there's always a surprise when you look at collective behavior. You know, even when something looks really coordinated and really cooperative, you have to look twice and see whether in actual fact, it's driven by aggression. 

Question: Will this new knowledge help solve the locust problem?

Iain Couzin: We now understand that this, you know, the limiting resources seem to be protein and salt in many circumstances. And so one of the big challenges with, I mean, there's no way we can just go and like pile loads of protein in these areas because frankly, if you can find the swarms, you may as well apply some sort of pesticides. 

The problem is finding them. I mean, they occur across vast areas, no one knows where the egg laying fields are, no one knows when and where these swarms are going to form. So if we can link together our understanding of the biology with our understanding of weather patterns, geography, using what's called hyper spectral imaging from satellites to give us some information about the protein content of vegetation, what we're hoping is it might be possible to actually start building predictive models and using the type of simulation techniques that we've developed to scale up from, you know, in detailed individual interactions up to the behavior of millions of individuals, we're hoping that we can make some breakthroughs in control.

Recorded on December 15, 2009
Interviewed by Austin Allen