No tool in Wildlife Services' arsenal kills more nonselectively – or slowly – than the leg-hold trap.

Since 2000, more than 90 species of wildlife have died by mistake in agency traps, including pronghorn antelope, mule deer, river otters, swift foxes, badgers, porcupines and federally protected bald eagles, government records show.

But whether animals are caught accidentally or not, they often struggle for days and die of exposure, injuries and other causes long before a trapper returns to the site.

"They suggest traps be checked once a week, but that's all it is, a suggestion," said Gary Strader, a former Wildlife Services trapper in Nevada from 2006 to 2009. "There are traps that are not checked for literally months at a time."

By then, little is left but steel and bone. "I've found traps that were Wildlife Services that were never checked, come across them years later with skeletal remains of skunks or badgers or coyotes," said Tony Wasley, a mule deer biologist with the Nevada Department of Wildlife.

Leg-hold traps have been banned in more than 80 nations and outlawed or restricted in eight states, including California, where voters in 1998 passed a proposition banning leg-hold traps, but allowing padded traps in some situations.

The device, which consists of two curved steel bars that snap together with extreme force, was invented in the early 1800s and has stirred controversy ever since.

"The leg-hold trap … is probably the most cruel device ever invented by man and is a direct cause of inexcusable destruction and waste of our wildlife," wrote Dick Randall, a former federal trapper, in a statement to Congress in 1975.

"Even though I was an experienced, professional trapper, my trap victims often included non-target species such as bald and golden eagles, a variety of hawks and other birds, rabbits, sage grouse, pet dogs, deer, and antelope, badger, porcupine, sheep and calves."

"My trapping records show that for each target animal I trapped, about two unwanted individuals were caught," Randall wrote. "Because of trap injuries, these non-target species usually had to be destroyed."

Leg-hold traps are used by Wildlife Services to capture and kill about 10,000 to 14,000 animals a year. Roughly half are coyotes, but more than two dozen other species are also targeted, from bobcats to beavers, mountain lions to wild pigs.

About 100 species of birds, mammals and reptiles have been caught and killed accidentally, too, including white-fronted geese, great blue herons, wild turkeys, hog-nosed skunks, mule deer, kit foxes, black-tailed jack rabbits and a wolverine.

Wildlife Services officials defend the traps, saying they almost always catch the intended animal. Of 80,800 animals captured in leg-hold traps since 2006, only 4,300 – or 5 percent – were non-targets, agency records show.

"If you look at the percentage of non-targets, it's really very low," said William Clay, the agency's deputy administrator.

But former employees said many non-target mortalities are not reported to avoid drawing attention to the agency.

"If all non-target animals were reported, Wildlife Services would be run out of business in a year," said Strader, the former trapper. "It would be scary to the public, the number of animals caught and killed."

Randall raised concerns, too, back in 1975. "Data concerning the destruction of non-target wildlife by leg-hold traps is largely nonexistent because unwanted species of wildlife are usually tossed behind a bush or into a ravine. Scavengers and decomposition make quick work of the carcasses," he wrote.

Clay said agency leg-hold traps are outfitted with "pan tension devices" that allow smaller animals to step on them without being captured. "Our policy is we want to minimize non-target takes," Clay said.

But Strader, who used the devices extensively, said they are not infallible. "They have been using those for years with very mixed results," he said. "It does help but still a lot of non-target animals get caught.

"I had a trap with the pan tension set at its highest (level) catch a raven by the head," he said. "There must have been something in the trap pan that drew his interest and he pecked at it with his beak and got caught."

In many cases, smaller animals that should have avoided capture were caught anyway when they stepped on the pan – which springs the trap – with two legs.

And larger animals would get trapped even at the highest tension setting, he said.

"I always used heavy pan tension so my small, non-target catch was real low," Strader said. "That being said, I would have a lot of traps out. So with the law of averages, I ended up catching about everything that could be caught."

In some cases, animals can be released alive if trappers find them in time. But records obtained through the Freedom of Information Act show that often doesn't happen.

"Mule deer died of exposure in trap," wrote one agency employee after checking a leg-hold trap set to catch a coyote in Nevada in June 2010. A month later, he trapped another by mistake: "Mule deer fawn died of exposure," he wrote.

Even when the right animals are captured, they often succumb in ways that would make many people cringe, including heat, thirst and exhaustion during the hot summer months.

"Remember, these animals have fur coats on," said Strader. "They exert themselves trying to get out. They over-stress with the heat and keel over and die.

"Most coyotes die this way, and when the trapper gets there, all that is left is a bunch of hair, bones and maggots," Strader said. "I've seen it hundreds of times and it always bothered me. It has to be a horrendous and torturous way to die."

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