More than two decades into Texas’ ever escalating war against feral hogs, the wild swine continue gaining ground while Texas and the state’s native wildlife, plants and ecosystems lose it.
Despite taking millions of casualties – an estimated 750,000-plus feral hogs have been killed each of the past few years in Texas – the non-native pigs have continued their economically and environmentally destructive march across the state, with an estimated 2.6 million of them spread across at least 240 of Texas’ 254 counties.
“It’s just getting worse and worse; no matter what we’ve tried, the hogs just overwhelm us,” said Stuart Marcus, manger of the 25,000-acre Trinity River National Wildlife Refuge. “They certainly are having a negative impact on native wildlife and habitat – directly and indirectly.”
Texas holds, by some estimates, as many as 10 times the number of feral hogs it did barely three decades ago.
A research project by Rice and Texas A&M universities conducted in the Big Thicket of southeast Texas used fenced and unfenced plots of land to gauge impacts of feral hogs. The plots used by hogs saw plant diversity reduced, fewer forbs, fewer large-seed (mast producing) trees, loss of leaf-litter ground cover resulting in a reduction in the abundance of invertebrates and small vertebrates, and changes in soil chemistry that changed plant communities.
The research also indicated plots disturbed by feral hogs grew twice as many Chinese tallow trees as the hog-free areas. Tallow trees are one of the most problematic non-native, invasive plants threatening Texas, as the tallows grow in dense monocultures, shade out native trees and grasses, are of almost no value to wildlife, and are almost impossible to control.
Stuart Marcus witnesses this on the Trinity River refuge.
“I call feral hogs ‘walking tallow trees,’ ” he said. “They are just as bad as tallow trees, and wherever they root up the ground, tallow trees seem to sprout by the hundreds.”
Feral hogs’ rooting behavior causes severe damage to environmentally sensitive and hugely important areas along waterways, particularly in central, south and western Texas where such waterways are limited.
“They definitely impact plant communities and really do serious damage to riparian areas, especially the western half of the state,” Frels said.
For the past three years, research at the Kerr wildlife area has focused on sodium nitrite, a toxicant that has been used to great effect against feral hogs in Australia.
Sodium nitrite kills by disrupting blood’s ability to carry oxygen to the brain. Pigs are highly susceptible to sodium nitrite because, unlike humans and other mammals, they lack the ability to produce an enzyme that reverses the effects. A feral hog ingesting a lethal dose of sodium nitrite quickly becomes lethargic, then unconscious. Death occurs within 90 minutes.
Research indicates the poisoned pigs pose little or no threat to scavengers or predators.
Developing bait/sodium nitrite mixtures that feral hogs will eat and that deliver a lethal dose of the substance and a “delivery system” – a feeder – that feral hogs can access but can’t be used by deer, raccoons and other non-target wildlife are the focus of research at the Kerr.
“It’s showing some promise,” Frels said of sodium nitrite’s potential as another tool to use against feral hogs. “But there’s still a long way to go before it could become an option.”
If it does, it could help turn the tide in the battle against feral hogs. In Australia, use of sodium nitrite has reduced feral hog populations in large areas by as much as 89 percent.
That would be a game-changer, and we could sure use it. I just hope the hogs don’t develop an immunity to it, at least not for a long time. Good luck getting it developed.