Feral swine and Burmese pythons are both interlopers in the United States, spreading through public lands and altering ecosystems. To arrest the invasion, ecologists are tagging “Judas” animals to follow them into their communities, learn their behaviors, and then take them down.

The hog problem is old compared to the more recent Burmese Python invasion in southern Florida. The pigs arrived in Louisiana in the 1500s, likely on the ships of Spanish explorer Hernando De Soto.

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But in the last two decades, the pigs have gone hog wild expanding their range. Feral swine maps from 1982 onwards show a steady progression from the southern United States into the West and as far north as Michigan. Biologist Stephen Hartley of U.S. Geological Survey (USGS) in Louisiana works closely with hunters to track the swine. Hartley is an avid hog hunter himself, so the project is a natural fit.

No one knows why the population has expanded so rapidly, he says. Ecologists estimate there may be between 300,000 and 400,000 hogs in Louisiana alone.

To get a better handle on the population, Hartley collaborates with hunters to catch, collar and release wild hogs. He started out with 15 pigs, and lost five of them (due to deaths or equipment malfunction). The GPS-collars transmit their location to a satellite, which beams the information to a Google Earth app on Hartley’s desktop.

So far, he has found that the hogs prefer marshy areas and their favored home range spans two square miles.

“In the marsh, they are sleeping where they are eating,” said Hartley.

These feral couch potatoes will occasionally move about during the day, but they are most active in the early hours between two and five a.m.

Once he has enough information, Hartley either sets out a trap to catch the tagged individual at its hotspot or lets his hunter friends know where the group’s bedding ground is located. After that it's hog heaven.

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Tracking Florida's snake problem is a little more slippery.

The Asiatic constrictor snake can weigh more than 200 pounds, reach up to 20 feet, and yet is almost invisible in the dancing grasses of the Everglades National Park. The python’s ability to hide, together with a rapid reproduction rate -- females lay clutches averaging 35 eggs -- has allowed them to proliferate.

Since the animals became established in 2000, the populations of mid-size mammals in the park such as rabbits, bobcats and foxes has decreased, according to a study in the Proceedings of the National Academy of the Sciences. And yet, scientists know little about the pythons.

To get more information, Kristen Hart, a biologist with USGS’ Southeastern Ecological Science Center, began the “Judas” snake project in 2008. She captures males in the breeding season and does minor surgery to implant into their muscle an array of devices the size of a AAA battery covered in biocompatible material. Two radio tags lead scientists carrying VHF receivers directly to the animals. A GPS tag logs information about the past locations of the snake. The data will, over time, reveal the behavior of these snakes in their new territory. But the more urgent need is to capture and kill.

Scientists tracking males in the breeding season find their targets entangled with a female. The capture rate through the Judas snake system is comparable to using traps, Hart said. Both the mating animals are then killed.

“The animals have such an impact on the environment, they have the ability to decimate our native animals -- mammals or birds,” Hart said. “The Everglades needs to have them removed.”