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In the United States, the wild hogs with the longest pedigree are descended from ones that escaped from Polynesian Islanders who first brought pigs to the Hawaiian Islands in about 750 A.D. This strain eventually reinvigorated itself by crossbreeding with escapees from later Hawaiian settlers; many places in the Islands have a vexing wild-pig problem today. The first feral pigs in continental North America deserted from the expedition of Hernando de Soto, the Spanish explorer who crossed the Southeast to beyond the Mississippi River in 1539–42. Wild pigs that got away from Spanish colonists in Florida survived in the woods and swamps so successfully that today some of their descendants represent the only modern examples of old Spanish breeds that long ago disappeared in domestication.
In frontier times, farmers let their hogs run loose, then collected them with the help of dogs on butchering day. Many hogs chose to skip this event, naturally. After America became rich, circa 1890, sportsmen with money imported Eurasian wild boars to stock hunting preserves. When these animals escaped and crossbred with feral swine, they created a tougher and even better-adapted (some say) feral hog. The fact that wild swine have been living in America for centuries does not dissuade wildlife biologists from referring to them as a “non-native” species. Feral hogs of the species Sus scrofa live on every continent but Antarctica, and also on many islands and archipelagoes. Except in the original range of the Eurasian wild boar, feral hogs are non-native everywhere.