Florida is facing a dangerous foreign invasion—but the enemy is not human. Burmese pythons have spread from the southern tip of Everglades National Park to most of southern Florida in the last 20 years, according to a comprehensive study by the U.S. Geological Survey. The invaders, which can grow to over 18 feet in length, were first brought to the U.S. as exotic pets in the 1970s, but have since spread into the wild and may now number in the tens of thousands. The snakes now pose a significant threat to local ecosystems, as researchers blame them for an 85 percent to 100 percent drop in mammal sightings within Everglades National Park. There is no consensus on just how far the so-called “invasion front” could spread, but some studies have predicted that the Southeast Asian snakes could proliferate across Florida and even much of the southern United States. In the meantime, researcher Jackie Guzy says “there are no easy solutions” to stopping the spread, though the state is trying everything from tracking devices to a 10-day python-hunting challenge.