It looks like the Giant African Snail that was discovered in Houston, Texas, was actually a Rosy Wolf Snail, which is native to North-America (it is considered an invasive species in some places, like Hawaii, but not in Texas).
Turns out the big snail found in a Houston garden is beneficial, not bad. It was a rosy wolf snail, a predator of snails that devour garden plants, said Michael Warriner, invertebrate biologist with Texas Parks and Wildlife Department.
Photos of the suspicious snail tipped Warriner to its identity. Both the rosy wolf snail and the giant African snail have appendices for seeing and smelling. But the rosy wolf snail has a third set, oral lappets, that help it locate other snails' slime. It then grabs its prey and rasps it with its radula, which works like a rough tongue, Warriner explainedIn addition to its extra appendices, the rosy wolf snail matures to 2 or 3 inches, considerably smaller than the potentially 8-inch giant African snail, Warriner said.
"It's not uncommon for the rosy wolf to be mistaken for the giant African snail," said Tanya Espinosa, public affairs specialist at U.S. Department of Agriculture. (source)