Dressed in black like commandos, assault rifles over their backs, the officers revved up their new all-terrain vehicles and roared into the woods in search of illegal loggers.

"There are well-armed mafias out there," said Elias Martinez, 22, as he bounced over the gravel road. "But since we've been patrolling, we haven't seen any of that activity."

These are the butterfly police, Mexico's latest effort to protect the forest sanctuaries where millions of monarch butterflies are arriving again after a wondrous and little-understood annual migration across thousands of miles from southeastern Canada.

With deterrents such as the new patrols, the government says it has nearly eradicated the logging that denudes hillsides where the butterflies nest. But critics insist the logging continues unabated, while leaders of a key village threatened to start cutting again this year if the government does not come through with alternative sources of income.

When Mexico's Monarch Butterfly Biosphere Reserve was created 19 years ago, about 10,000 villagers were asked to give up logging in exchange for tourist-related jobs and a special compensation fund. But some complain that the money runs out soon after the last of the butterflies and tourists visit between November and March.

"You can't eat butterflies," said Abel Cruz, 44, leader of Rosario Village, host to the most monarchs and monarch watchers every year. "If the government doesn't comply with what they promised, we are not going to comply either."

Reserve officials believe the threats are partly a strategy to get more money. But it illustrates Mexico's difficulty in finding a balance between protecting a globally valued natural treasure and the impoverished people who have shared the hillsides with them for generations.

The goal is to make partners of the insects and the people, rather than rivals over use of the woods about 100 miles west of the capital.

"We've got the eyes of the world on us," said Eduardo Ramirez, director of the reserve. "If you have a 3-year-old crying with hunger, what are you going to do? That's the challenge, and why we have to keep pushing to convert these threats into proposals."

Officials say they expect a big rebound this year in the number of monarchs arriving in Mexico. Last year saw a precipitous fall when only 22 million showed up, down from 112 million in 2003-04.

Such periodic drops can be linked to cold spells. But experts fear the long-term survival of the monarchs is threatened by pesticide use in the United States and Canada and the loss of nesting habitat in Mexico.

A visit to one of eight sanctuaries inside the reserve can be awe-inspiring. At the height of the season, in January or February, the forests can turn orange with monarchs swarmed together on the branches of every tree, accompanied by a symphony of softly fluttering wings.

Scientists don't know exactly how the young monarchs find their way 3,000 miles from Canada without ever having been in Mexico before. After breeding, they will die on their return trip north through the United States. A later generation of their offspring, who are born up north, will make the trip south the next winter to the same Mexican hillsides.

Mexican officials say the biggest local threat to the insects are armed logging gangs with ties to organized crime. But, through police work and checkpoints, they say they have eliminated 85 percent of the gang logging.

The state government of Michoacan announced the creation of the 26-member forest patrols last month.

"We have effectively disarmed the bands," said Francisco Luna, the Michoacan delegate for Mexico's federal environmental enforcement agency.

But environmentalists and tourism operators say that assessment is way too optimistic. They say the gangs continue to thrive because of corruption and the government's lack of resources to effectively patrol a 185,000-acre reserve.

"The foreigners go into the sanctuaries and listen to the chainsaws and say, 'I thought this was a sanctuary!' " said Pablo Span, a hotel owner in the area. "Every single day these forests are being logged."

The dispute with Rosario has brewed since the government expanded the reserve and limited locals' use of the forests in 2000; communal leaders say that cost the village $1 million. They want permission to cut again three miles from the butterflies' nesting areas.

They also complain about not receiving money from the $6.5 million Monarch Butterfly Conservation Fund, designed to compensate villages for not cutting trees. Officials respond that Rosario was one of seven villages that chose not to join the program when it began in 2002, while 31 others did. They say they expect Rosario to apply now.

"There was a little mistrust, people saying, 'They're going to take my land,' " said Juan Antonio Reyes, who coordinates the conservation project for the World Wildlife Fund. "Now that a few years have passed, we're reaching out to them again."

Luna said the villagers earn as much as $2.5 million each year from tourism, including $3-per-adult entrance fees, parking, guided tours and horseback tours. They also sell pine-needle baskets and monarch-themed crafts from shacks that line the tourist paths.

The government has tried to help create jobs in reforestation, trail maintenance and trout farming during the off-season, while building access roads and other tourist facilities and promoting methods to reduce local wood consumption.

Long term, the villagers dream about projects such as developing a small factory to produce the monarch-emblazoned T-shirts they sell. Now the T-shirts are brought in, and the profits go out.

As it is, Rosario villagers say persistent poverty has contributed to the departure of at least 200 young men for the United States in search of work.

"What we need is for everyone in the world to know that we have the biggest monarch reserve in the world, and we need more and more tourists to come," said Ruben Garcia, 59, Rosario's security chief. "But right now, it's not enough."

A sanctuary created for migrating monarchs is said to hurt local residents.Monarchs gather in Pacific Grove, Calif., as they travel from Canada to Mexico.