The researchers found that forest areas with feral pigs had 26 percent less diverse mammal and bird communities than other forests, partly because the voracious ominvores eat plants, animals and fungi, and out-compete other animals for food. In other words, "Wild pigs are a serious threat to biodiversity," Marcus Lashley writes for The Conversation. Lashley is an assistant professor of wildlife ecology at Mississippi State and the lead author of the study.
All that adds up to a lot of expense. In the early 2000's it was estimated that feral hogs caused $1.5 billion in damage each year in the U.S. Their population has grown by 30% and their territory has grown by 40% since then, so their economic impact has likely increased. Since the 1980s, feral pig populations have nearly tripled and have expanded from 18 to 35 states, Lashley notes.
"Another major concern is feral pigs’ potential to spread disease. They carry numerous pathogens, including brucellosis and tuberculosis, Lashley writes. "However, little ecological research has been done on this issue, and scientists have not yet demonstrated that increasing abundance of feral pigs reduces the abundance of native wildlife via disease transmission."
Here's a Farm Bureau video of farmers and scientists describing damage from feral pigs in Missouri: