Billions of desert locusts have descended again on East Africa. Crawling first, then sprouting wings and flying in hungry hoards of 40-150 million or more, they are devastating crops and threatening tens of millions of people with lost livelihoods and starvation. This year’s plague, says the United Nations, is the worst in 70 years for Kenya, the worst in a quarter-century for Ethiopia, Eritrea, Djibouti and Somalia. Locust swarms can blanket scores or hundreds of square miles at a time, travel 80 miles a day, and consume more than 400 million pounds of vegetation daily, Africa Fighting Malaria cofounder Richard...