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.

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.

Monarch butterflies gather on a tree branch Wednesday at the Monarch Butterfly Biosphere Reserve in Sierra Chincua, Mexico. Rangers protect the winter nesting grounds of millions of butterflies from armed gangs of illegal loggers.

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.

Mexican authorities aim to have more than 100 officers by the middle of next year, supported by volunteer patrols, mostly consisting of local farmers.

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.