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Religion and locusts go way back. There’s an old yoga pose (lying on the stomach, arms and legs raised) called “the locust” for Hindus and Buddhists, and people in ancient Greece worshipped a locust God sometimes linked to Apollo. In China ancient locust cults with temples persist even today. Most notably, fourteen separate books in the Judeo-Christian scriptures make reference to these small, voracious, and unfortunately extremely social pests.
In most cases in the Bible—like the time Moses inflicts a sun-blotting plague on Pharaoh and Egypt—the locusts are directly guided by Yahweh’s hand to carry out His planned vengeance. Yet there’s at least one dissenting view: “The locusts have no king,” says Proverbs 30:27, “yet go they forth all of them by bands.” That is, despite the lack of any alpha leaders or whispers from God, locusts still manage to move forward in tandem.
That view of leaderless swarms of locusts is biologically accurate. In fact, the incredible coordination of the swarms has always puzzled biologists, who could never figure out how lowly bugs “knew” how to move in groups. Now, however, a transatlantic team of scientists has figured out what coordinates these bugs, and it turns out to be just as awful as anything wrought in the Bible—cannibalism.
Locusts eat mostly plant matter, which is low in salt and protein, explains Iain Couzin, an assistant professor of ecology and evolutionary biology at Princeton University and senior scientist on a recent paper in Current Biology. Often, the only edible protein and salt nearby is other locusts, so the bugs tend to hop onto each other’s backs inside swarms and start chomping on their neighbors.
Cannibalism had been reported in swarms anecdotally, “but we were the first to show this is not some accident,” Couzin says. His group determined that the locusts have evolved sensors to detect movement from behind, and the direction that each bug jumps to escape brotherly predators (and to go after brotherly prey) will move the swarm ahead. Individuals may jump a little right or left, but over a large scale, small deviations cancel out, and the bugs leap ahead in what appears to be a directed fashion.
“In Victorian times, people believed there had to be some sort of telepathy among the individuals,” Couzin says. “What we found is that we don’t need that sort of pre-concerted arrangement. On an animal level, you don’t need the conductor.”
That’s pretty amazing, considering that locust clouds can swell to truly biblical proportions. Some have populations that reach into the billions. Doing fieldwork in Mauritania, Couzin says, “I walked around one with a GPS unit. It was 17 km [10 miles] in circumference.” And while the bugs tend to eat what’s right in front of them, locust clouds can sometimes catch a strong wind and blow for miles. One swarm once surfed from Africa to Jamaica on a particularly good breeze.
Other species like fish also move in schools, but so far the cannibalism in locusts is unique among social animals. Unfortunately, figuring out how and why the swarms move is more than an academic interest. Locusts don’t eat people or animals, but they eat acres and acres of what people and animals like to eat. Crises in Southeast Asia and especially Africa are often exacerbated by locust swarms that wipe out crops and put pressure on the human population to find food through whatever means are necessary. The United Nations has long tracked and monitored locust activity for humanitarian reasons.
Of course, there might just be a solution to all this in the locusts themselves, which are perfectly edible. The book of Leviticus explicitly licenses people to munch on locusts, and John the Baptist subsisted on them (along with “wild honey”) during his pilgrimages in the desert. And as late as 2004, a fatwa in Egypt said that if locusts are eating crops, Muslims should feel free to eat them in turn. After all, the locusts themselves understand perfectly how tempting a locust can be.
Sam Kean is the associate editor of Science & Spirit.
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