In the last two decades, the Gulf Coast has experienced an unwelcome invasion. Nonindigenous apple snails, native to South America, have made nuisances of themselves in the freshwater ecosystems of Florida, Texas and Louisiana. For that reason, wildlife officials in Louisiana in particular have encouraged the public to destroy the apple snails’ pink egg clusters — and to be careful while doing so. In a video posted to YouTube last year, crawfish specialist Mark Shirley of the Louisiana State University AgCenter explained the origins of the state’s apple snails, how to spot their eggs and how …