With three helicopters also on butterfly patrol, police have arrested at least 28 members of a so-called "logging Mafia", seized 380 trucks with their consignments of about 4,000 cubic metres (5,250 cubic yards) of timber, according to the federal environment prosecution service (Profepa).

The Monarch, or Danaus Plexippus, butterflies migrate 5,000 kilometers (3,100 miles) from Canada each year.

President Vicente Fox announced on taking office three years ago that he would propose a strategy to protect them.

A 16,000 hectare (40,000 acre) reserve of pine trees was this year increased to 56,000 hectares (138,000 acres). The forests contain the food for the Monarchs and protects them from the cold winds that hit the Michoacan state region in winter.

Satellite photos have shown that the reserve is becoming encircled by farmland and that each year about 300 hectares (740 acres) of forest is illegally cut down, according to Carlos Galinda-Real, a coordinator of a Mexican forestry programme for the World Wildlife Fund for Nature.

The Mexican authorities say they are replanting 2,000 hectaresacres) each year however.

"It is not just Mexico that is in political transition; so is its environmental policy," said Michoacan governor Lazaro Cardenas Batel.

The big orange and black Monarchs spend each summer in the north of the United States and Canada. They head for Mexico each winter to reproduce and then head back north every March.

They are special among butterflies because they live for nine months, while ordinary species last only a few days or weeks.

Scientists have been researching the secret of their longevity for 26 years.

They are also unusually strong, able to cover up to 80 kilometersmiles) a day on their two month flight from Canada.

The Aztecs believed that the Monarchs were reincarnations of their dead warriors.

Researchers wonder how they find their directions, with theories ranging from their genetic makeup to an ability to follow the Earth's magnetic field.

The Monarchs lay their eggs under the poisonous leaves of Milkweed plants. The larvae eat the leaves without any ill-effect of the poison. But the poison also keeps potential predators -- lizards, wasps and birds -- at bay. But not man.

TERRA.WIRE