From Texas Monthly:
With a population now exceeding 2.6 million, feral hogs in Texas have hit critical mass. Females can have up to two litters a year, with an average of five to six piglets each, and they are outbreeding deer, humans, and every other large mammal in the state. Like many creatures of the night, they roam in packs, long-toothed and short-tempered, willing to eat nearly anything, including their young.
If you were to invent the perfect invasive animal, you could not do much better than a hog. Smarter than dogs and as fast as deer, they are also extremely tough. While many of the stories about bulletproof hogs are apocryphal, some of the larger boars do have a gristle plate that will stop a bullet fired from a handgun—my father once shot one with a .357 Magnum, only to watch the animal shake it off and walk away.
For more, see: Whole Hog