This time a year ago, experts were already predicting the return of flesh-eating screwworms to the United States: a matter of not if but when , Wayne Cockrell, a Texas rancher, lamented to me at the time. Screwworms had been eradicated from the U.S. to Panama and then were cordoned off through the continual release of almost 20 million sterilized screwworms every week over the narrow Isthmus of Panama. But screwworms, which grow into flies as adults, had jumped the cordon and infested a large