Some are abandoned pets; others were born on the streets. In order to survive, these social creatures form packs, scavenging garbage or killing livestock in teams.

In rural communities, wild dogs attack livestock, angering farmers who commonly shoot them. A survey by the National Agricultural Statistics Service in 1999 found that feral dogs were partly responsible for killing cows, sheep, and goats worth about U.S. 37 million dollars.

Farms aren't the only place where these animals may be found. Low-income, high-crime neighborhoods in cities like Los Angeles, St. Louis, New York, Santa Fe, Pittsburgh, and Cleveland, are being overrun by tens of thousands of unwanted dogs, says Randy Grim, founder of Stray Rescue in St. Louis, a nonprofit organization that saves street dogs.

"The problem is only going to get worse," he said. "Animal control agencies and humane societies don't want to deal with it. It's just too overwhelming."

The problem started in the 1980s, Grim said, springing from a combination of increased dog fighting, dogs being bred for aggressiveness, and reduced animal control. Compounding the problem, he said, is that America's poorest neighborhoods do not have veterinarians or animal shelters.

In Detroit, packs of free-roaming dogs have posed such a danger that a postal service spokesman said they considered stopping mail delivery to some areas last year because carriers were "constantly being bitten" or injured eluding vicious animals.

In St. Louis, a 10-year-old boy was attacked and killed two years ago by a pack of stray dogs. Police Chief Ron Henderson told the St. Louis Post Dispatch: "They were feeding off this kid. I've seen over 1,500 bodies but I've never, never seen anything like this. Nobody has."

And it's not just a problem in the United States-it's worldwide.

According to some estimates, the current world population of domestic dogs may be as high as 500 million, of which a substantial, although unknown, proportion is free-roaming.

There have been news reports of feral dogs causing havoc in Australia, India, Russia, Taiwan, and Turkey.

In Greece, more than U.S. one million dollars is reportedly being spent on rounding up, sterilizing, and vaccinating thousands of street dogs in Athens before the 2004 Olympic games.

Most towns and cities across America have strong animal-control programs and veterinary services that keep the pet population in check, protecting citizens. But not all communities have that luxury.

The Rosebud Sioux Indian Reservation in South Dakota, where 23,000 people live, is one of the poorest counties in the nation.

The animal population on the reservation is at crisis levels. An estimated 4,000 dogs, covered with mange and ticks, roam the land and are sometimes so hungry they resort to cannibalizing other dogs.

The reservation does not have a veterinary hospital, and each week Indian health officials investigate an average of two dog bite incidents, often involving children.

"The animals need to be healthy in order to have a healthy community," said Karen Santos, Companion Animals Project Coordination for the International Fund for Animal Welfare (IFAW.)

In July, the nonprofit organization, along with other animal welfare groups, held a five-day clinic on the reservation, spaying and neutering 980 cats and dogs.

"Fixing the animals makes them less aggressive," explained Santos. This in turn, she added, will help reduce the extraordinarily high number of bites that occur on the reservation.

The clinic's staff also provided treatment for mange and vaccinations.

The program is the first time a humane approach to control the number of pets on the reservation has been carried out. A shoot-and-kill policy, she said, was previously in place.

Another clinic is being planned for May.

The IFAW also has sterilization programs in Turkey, Russia, the Indonesian island of Bali, and the Navajo Nation in Arizona-all aimed at reducing feral dog populations.

In St. Louis, Randy Grim, founder of Stray Rescue, is out on the streets everyday feeding 50 or more mutts.

If these wild dogs don't die of sheer starvation, he said, diseases such as parvovirus, heartworm, or intestinal parasites usually kill them. Their average life span is one to two years.

Many of the animals he sees were once "bait dogs"-smaller, passive animals used to train fighting dogs. Great Dane puppies are commonly used, he said, and wire is twisted around their legs to hold them down, so they can't run while being mauled during training sessions.

"If they live, they are just discarded onto the streets," said Grim. The animals are recognizable by their missing limbs, and scars from the brutal attacks.

Since starting in 1991, Grim is credited with saving 5,000 feral dogs, all of which-through months of gentle, loving care-have been turned into house pets and adopted by new families. Some have even gone on to become therapy animals, bringing joy to people in hospitals and nursing homes.

A book on his rescue triumphs and struggles was published this year, entitled The Man Who Talks To Dogs (St. Martin's Press, Melinda Roth.)

In between interviews and speaking engagements, Grim has found time to start a new program, called Operation East Side, that offers free spaying and neutering and medical care for dogs in low-income areas of St. Louis. He hopes to make it a model program for other cities to follow.