Locust Swarms in East Africa Possibly Triggered by Irregular Changes in the Indian Ocean Dipole

by Saarang Kashyap

Gigantic swarms of desert locusts resembling dark storm clouds are descending furiously on the Horn of Africa. These locusts have a single mission: to eat as much as they can, and in the process, destroy plantations of crops, leading to an unprecedented threat to food security. On the ground, subsistence farmers can do nothing but watch — staring up with horror and at their fields in dismay.

As stated in NPR, locusts usually exist in their “grasshopper phase” — they lead solitary lives, they’re green and pretty unremarkable. The timing of this varies, and the shifts are pretty irregular, but for years, locusts can live like this — alone, biding their time. But when environmental conditions are right — usually when there’s a lot of rainfall and moisture — something dramatic happens: the locusts increase in number and sense fellow locusts around them. Though scientists can’t be certain why locusts developed this trait over time, many believe it’s because they typically live in temperamental and harsh environments.  Rick Overson of Arizona State University’s Global Locust Initiative explains how the variable climate of the Horn of Africa may bring about locust swarms, stating “The Horn of Africa is known for being arid, going for years without heavy rain until slammed suddenly by powerful downfalls. The strongest hypothesis is that these crazy, unpredictable dynamics select evolutionarily for this ability to go through these dramatic changes, to respond when you can capitalize on a rare opportunity and also have capacity to migrate.” Essentially, the flies have adapted an ability to change from a sedentary to a swarm lifestyle based on environmental conditions. 

How numerous and powerful are these swarms? NPR mentions that “the swarms are gargantuan masses of tens of billions of flying bugs. They range anywhere from a square third of a mile to 100 square miles or more, with 40 million to 80 million locusts packed in half a square mile. They bulldoze pasturelands in dark clouds the size of football fields and small cities.” In Kenya, it’s the worst outbreak they’ve had to face in the last 70 years, and in India or Pakistan, it’s probably the worst they’ve had to face in the last quarter of a century.” How fast can locusts travel? “They are powerful, long-distance flyers, so they can easily go a hundred plus kilometers in a 24-hour period,” Overson notes. “They can easily move across countries in a matter of days, which is one of the other major challenges in coordinated efforts that are required between nations and institutions to manage them.”

How does climate change factor into this?

The unusual wet weather in East Africa is linked to a wider climate system known as the Indian Ocean Dipole (IOD). The IOD was in its positive phase in the June to December period of both 2018 and 2019. In 2019, the dipole reached its most extreme positive level in 40 years. Scientists hypothesize that this change has created the perfect conditions for locust swarms.