Despite a reputation for gluttony and poor hygiene, pigs are actually highly intelligent animals. Both domestic and wild species are known for their ability to adapt to a variety of different ecological conditions. They seem to be at least as trainable as cats and dogs, and certain domestic pigs have become a favorite pet in the U.S. Pigs are also extremely flexible. Unlike most other ungulates, which are strictly herbivorous, pigs and their relatives are omnivores with a diet that sometimes includes worms and small vertebrates. Where they have been introduced around the world, pigs tend to out-compete the native species. Though devastating to the native species, this trend is yet another strong indication of pig cleverness.