A swarm of locusts is awe inspiring and terrible. It begins as a dark smudge on the horizon, then a gathering darkness. A rustle becomes a clatter that crescendos as tens of millions of voracious, finger-sized, bright yellow insects descend on the land. Since late 2019, vast clouds of locusts have shrouded the Horn of Africa, devouring crops and pastureland—and triggering an operation of staggering proportions to track and kill them.

So far, a ground and air spraying campaign over eight East African countries, coordinated by the United Nations Food and Agriculture Organization (FAO), has staved off the worst—the very real prospect that the locusts would destroy the food supply for millions of people. Last year, the operation protected enough pastureland