East Africa is in the midst of a crisis that sounds like something out of the Book of Exodus: A plague of locusts is spreading across the region, threatening the food supply of tens of millions. City-sized swarms of the dreaded pests are wreaking havoc as they descend on crops and pasturelands, devouring everything in a matter of hours. The scale of the locust outbreak, which now affects seven East African countries, is like nothing in recent memory.

The insects behind the mayhem are desert locusts, which, despite their name, thrive following periods of heavy rainfall that trigger blooms of vegetation across their normally arid habitats in Africa and the Middle East. Experts say a prolonged bout of exceptionally wet