SIERRA CHINCUA, Mexico -- With assault rifles over their shoulders and body armor strapped to their chests, Roberto Paleo and his 17 officers are among the world's most heavily armed park rangers. Yet they guard one of nature's most delicate creatures - the monarch butterfly.
The rangers say they need the weapons to protect the winter nesting grounds of millions of orange and black winged butterflies from armed gangs of illegal loggers in the Monarch Butterfly Biosphere Reserve.
The monarchs are not listed as endangered, but scientists say the deforestation could threaten their existence.
Although a single butterfly can spend its entire life in the United States or Mexico, they are born with the instinct to migrate.
Most do - traveling in the millions from Canada to a mountainous area in central Mexico each year to carpet fir trees that provide shelter, an aesthetic and scientific wonder that attracts about 200,000 visitors annually.
"The forest is like a blanket and umbrella to protect the monarchs from the cold winters," said Lincoln Brower, professor emeritus of zoology at the University of Florida who has been studying the butterflies for nearly 50 years. "If the forest disappears, we could lose one of the wonders of nature."
Last season, 22 million monarchs reached the park, an 80 percent drop from the previous year, prompting the Mexican government to set up the special police force.
Aided by hidden video cameras and communicating with special radios to avoid scanners, the officers speed around in all-terrain vehicles, looking for loggers in the rugged area, which spans more than 124,000 acres.
Their arsenal includes AR-15 and Galil automatic rifles, pump-action shotguns and Smith & Wesson handguns.
Mexico's illegal logging trade generates millions of dollars a year. And while the rangers have seized eight pickup trucks full of timber, they have yet to catch a logger, Paleo said.
Still, Francisco Luna, the Michoacan delegate for Mexico's federal environmental protection agency, says the mere presence of the police has deterred many logging gangs.
"They know we are here and that we are going to take away their vehicles and arrest them," Luna said. "Stealing lumber from the reserve is simply not worth it now."
Some environmentalists worry the small police force may not be enough to fight the gangs.
In 2003, a group of 100 loggers armed with shotguns and machetes held three park rangers hostage for six hours while they chopped down trees.
"These loggers are heavily armed, organized groups who are sometimes linked to drug traffickers," said environmentalist Homero Aridjis, a Michoacan native who has been campaigning to protect the monarchs for three decades.
Mexican authorities aim to have more than 100 officers by the middle of next year, supported by volunteer patrols, mostly consisting of local farmers.
"We have to protect the forest to keep the supply of water we need for our crops," said farmer leader Juan Rojas, standing with a group of 20 farmers. "And we want to look after the butterflies. They are part of our patrimony."
Many tourists come to see monarchs hanging from the trees during their November-March nesting season, bringing much needed cash into a local economy that survives largely off of money sent home by migrants in the United States.
Scientists have only tracked the butterfly numbers for the past decade, so it is difficult to know whether last year's population drop is normal.
Mexican authorities believe the monarch population will rebound this year to more than 60 million.
"The monarch population changes enormously year on year," said Jose Bernal of Mexico's environmental protection agency. "We haven't studied it long enough to see a pattern yet. It is alarmist to say the population is in danger of disappearing."
Still, Brower says there is irrefutable evidence that the destruction of Mexico's forest is a threat to the butterflies.
"The monarch has become a symbol for cross border co-operation in North America," Aridjis said. "Let's hope it doesn't become the symbol of our common failure to protect the environment."