latimes.com

Invasive species are a natural disaster waiting to happen. In some cases, there is a very real danger to humans, such as the Burmese Python in South Florida. In many cases, the threat to humans is indirect, yet no less important, such as Saltcedar's ability to drain waterways. In all cases, the biggest risk is to wildlife habitats, as invasive species are experts in pushing out native plants and animals.

Especially in the last couple of decades, many invasive species have made headlines, warning the public to watch for and help prevent their spread, from the Emerald Ash Borer to the Zebra Mussel to the Asian Carp. All the while, another species has been stealthily avoiding this radar, spreading to all but three of the mainland states, and keeping mostly out of sight until their local populations grow larger than the available food sources.

Feral hogs are the cockroach of the wilderness, multiplying quickly, highly destructive, disease-carrying, and resilient to control efforts. Conservation and agricultural experts alike are calling for more attention to this mostly silent invader of the nation's woodlands, including those in parts of South Dakota and Nebraska.

"There are only three states that list these things [wild or feral hogs] as game animals," said John Mayer, environmental services manager at the U.S., Department of Energy's Savannah River National Laboratory in Aiken, S.C., and the nation's leading expert in feral hogs. "Typically, these things are listed as an invasive species."

When people think of feral hogs, what comes to mind is the wild hog - usually the Eurasian Wild Boar - which is common in the Southern United States, but the feral hogs that are more likely to cause problems here are domesticated pigs that either escaped or were released into the wild and have adapted to living without human influence. Wild boar and feral pigs also readily breed, creating hybrids that grow larger than the typical wild boar but with the same notorious mean streak.

In South Dakota, there have been reports of a feral pot-bellied pig population at Big Stone Lake on the Minnesota border. Usually kept as a pet, pot-bellied pigs can grow as large as 300 pounds and the males will grow tusks. There is also an incident of a lone feral pig shot near Madison. In Nebraska, both wild-hybrid and feral hogs have been a problem in various central and southern counties.

According to the University of Georgia's National Feral Swine Mapping System, the largest populations of wild or feral hogs are in Texas, California, Florida, Oregon, Arkansas, Louisiana, Alabama, Georgia, Missouri, Tennessee, South Carolina, and Kansas. But wild or feral hogs have been spotted in all of the mainland states except Delaware, Rhode Island, and oddly Wyoming. Wyoming is particularly concerned about feral hogs migrating into the state from the Platte River, but Nebraska Game and Parks Commission's control efforts have so far been adequate. Thirty-six states have verified breeding populations.

"They are so adaptable to environments, from cold Canada to the hot, humid southern forests to downtown cities like Fort Worth [Texas]," Mayer said.

Wild hogs were first introduced to the United States by European settlers, but the rapid spread occurred in the 20th century when zoo stock was sold to wild game ranches in Arkansas, Missouri, and Oklahoma. Ranches in Michigan imported stock from Canada in the 1980s and 1990s. According to Mayer, wild boar is among the most popular big game species in the United States, second only to whitetail deer.

"As we all know, wild boar is hard to hold and these ranches were all leaking wild boar through the fences," Mayer said, adding that by 1990, there were 2 million wild hogs nationwide. "Basically, they're taking over the country."

Feral hogs can quickly get out of hand once they become established in an area. They are gregarious, living in small family groups although groups of 100-plus hogs have been reported if there is easy access to food; aggressive, able to inflict injury or even kill animals and humans in their four-square-mile home range; and opportunistic omnivores, meaning that they eat mostly plants but, at times, animals.

"Basically, if they can get their mouth around it, they will eat it," Mayer said. "They have been known to kill lambs, rummage through garbage cans, and eat sticks. All kinds of objects have been found in their stomachs."

Feral and wild hogs are also prolific breeders, raising two litters of six to 12 piglets a year. They are able to get pregnant as young as three months of age, and to breed again when still nursing a litter.

"You hear in the literature that they can double their population in four months and triple it in a year," Mayer said. "Mathematically that may be possible, but there's a lot more mortality in the wild. Piglets are the most vulnerable. Once they reach two years of age, they're good unless they run across a hunter."

From an agricultural standpoint, they can greatly damage property, particularly crops, and are a harbor to a number of diseases that affect domestic swine and other livestock as well as humans. According to The Samuel Roberts Noble Foundation in Ardmore, Okla., feral hogs have been known to carry and transmit:

&middot Pseudorabies, a virus that attacks the central nervous system of swine, cattle, horses, goats, sheep, dogs, and cats;

&middot Swine brucellosis, a bacteria that causes infertility and abortion in swine as well as arthritis and meningitis in humans;

&middot Tuberculosis, the same bacteria that infects cattle and humans;

&middot Anthrax, a soil-borne bacteria that is often fatal if contracted by humans;

&middot Tularemia, a bacteria that is often transmitted to humans through tick bites or improperly cooked wild game; and

&middot Parasites, including fleas, hog lice, ticks, roundworms, kidneyworms, lungworms, stomachworms, whipworms, liver flukes, and trichinosis, the last of which is commonly transmitted to humans through undercooked infected pork.

Wild hogs do not grow as large as domestic swine. Males weigh in around 200 pounds, and females to about 175 pounds. They measure five to six feet long from nose to tail and stand 30 inches tall at the shoulder. The wild boar color pattern is a brownish black body with dark points on the feet, tail, ears, and nose and a white face and rump. However, feral hogs and hybrids can be any coloring, though most likely a solid black, reddish brown, or white; or with a white belt; or spotted with two to three colors.

They can run up to 30 miles per hour, jump a three-foot fence, climb a six-foot fence, swim two miles in open water, and are agile enough to turn a sharp corner and ascend steep inclines at high speeds. They also have a keen sense of smell, able to detect odors from seven miles away and 25 feet below grade. Their field of vision is 275 degrees and they can focus in on objects one mile away. They are normally diurnal, like whitetail deer, but will become nocturnal during hot summers or if threatened by daytime hunting, and they move daily according to supporting resources, up to 200 miles from their home range.

"Everyone has heard about the half-ton hog, the monster hog," Mayer said. "You can have wild hogs that big, but they didn't grow naturally that big in the wild. There are not enough resources in the wild to support that kind of growth. Someone is feeding them."

Signs that feral or wild hogs are nearby are rounded "W"-shaped footprints, wallows, rubs on trees and telephone poles, and resting beds or farrowing nests, which look like giant bird nests in a rooted-out depression on the ground. Their first defense is freezing and camouflaging, but their tusks are designed to maim and they will charge. According to Mayer, five to 10 people are killed annually worldwide by wild or feral hog attacks. They particularly don't like dogs and are more likely to become aggressive.

Current control measures are trapping and shooting, but Mayer said that these aren't working as quickly as the feral and wild pig populations are able to expand.

"They just cannot take out enough animals to make a difference," he added.

There is research on oral contraceptives that could be distributed through bait. Mayer also suggests that states allow open hunting seasons that let hunters to go in and take out as many animals as they want. Despite parasite concerns, wild pork is as delicious as domestic pork. It holds the same cooking recommendation as domestic pork, and as long as slaughter isn't done sloppily, the meat is as safe.

Whatever the future holds for wild and feral hog populations in the United States, Mayer predicts the number of hogs to continue to increase without intervention.

"It appears that the population tends to do better in areas that are warmer but not too hot," Mayer said. "Climate change is impacting a rise in the population, although expansion is unquestionably man-made."