Several years ago, some unwelcome visitors began making their presence known across rural Louisiana. They left uprooted crop fields, trampled tree seedlings and destroyed wildlife food plots in their wake.

The culprit? Packs of hungry, havoc-wreaking feral hogs. And the problem has only gotten worse, with Louisiana’s hog population doubling in the past decade to reach about 1 million today. It’s now estimated they cause $91 million in damage every year in the state.

Hunting and trapping can’t get rid of enough hogs to keep up with their fast reproductive rate. A sow can have two litters a year, with an average of six piglets per litter.

After eight years of work, LSU AgCenter animal scientist Glen Gentry and his team closed in on a more efficient solution: a sodium nitrite-based bait that kills hogs but has minimal impact on the environment and nontarget species. It’s even safe for hunters to consume meat from hogs that have eaten the bait. The team recently reached a major milestone, with a patent being issued for the bait in August. The journey, however, has taken many twists and turns.

Early on, scientists took interest in sodium nitrite as a toxicant because of its effectiveness and relative safety.

“It’s got a very marginal, if any, effect on the landscape because it converts so quickly to compounds that don’t cause lethal issues,” said Gentry, director of the AgCenter Bob R. Jones-Idlewild Research Station in Clinton.

The rapid breakdown of sodium nitrite, however, proved to be a double-edged sword. Gentry tried to find ways to stop it from converting to those harmless compounds too quickly — before hogs could eat it — before contacting LSU chemistry professor John Pojman for help.

Pojman and his graduate students found that adjusting the pH of the bait matrix to a slightly alkaline level would keep the sodium nitrite stable and lethal to hogs.

Another key question was how to get hogs to eat the bait. After several tries, the team found the magic ingredient to entice hogs: dehydrated fish.

The bait they’ve landed on is a golf ball-sized sphere with a texture similar to a gummy bear. It doesn’t break apart when bitten into, which is important to protecting nontargets that may be tempted by remnants.

Newer iterations of the bait matrix include a fluorescent ingredient that glows beneath a black light, making it easy to see whether any pieces get left behind. So far, Gentry hasn’t found any scraps of the bait on the ground.

“Pigs like our bait,” Gentry said, adding that he has seen the animals gobble down three, four and even five of the bait balls at a time. Just one sphere contains enough sodium nitrite to kill a 100-pound pig.

After consuming a lethal dose — which for feral swine is 188 milligrams per kilogram — they become sleepy and die within three hours.

“It’s a very humane death for these pigs,” Gentry said.

Gentry and research associate Ariel Bourgoyne are now focusing on developing a feeder to deliver the bait and expanding from pen trials to larger-scale hybrid field trials.

“It is definitely a light at the end of the tunnel situation,” Bourgoyne said. “I see the progress we’ve been making and it’s gratifying. It’s been baby steps, but if you look back over the eight years, we’ve overcome a lot of obstacles.”

He noted that the majority of funding for the bait work has come from stakeholder groups, including the Louisiana Soybean and Grain Research and Promotion Board.

“It’s the people that are directly affected by the pigs that have provided the funds for us to move forward with the research,” he said. “And for that, we’re greatly appreciative.”