World

Monarch butterflies begin entering Mexico for annual migration to central pine forests

FILE - In this Jan. 4, 2015 file photo, monarch butterflies perch on a twig at the Piedra Herrada sanctuary, near Valle del Bravo, Mexico. Monarch butterflies have begun entering Mexico on their annual migration from the United States and Canada in October 2015. Mexico's Environment Department said Thursday, Oct. 8, 2015 that the butterflies had been spotted by park rangers entering Coahuila state, on the border with Texas. (AP Photo/Rebecca Blackwell, File)

FILE - In this Jan. 4, 2015 file photo, monarch butterflies perch on a twig at the Piedra Herrada sanctuary, near Valle del Bravo, Mexico. Monarch butterflies have begun entering Mexico on their annual migration from the United States and Canada in October 2015. Mexico's Environment Department said Thursday, Oct. 8, 2015 that the butterflies had been spotted by park rangers entering Coahuila state, on the border with Texas. (AP Photo/Rebecca Blackwell, File)  (The Associated Press)

Monarch butterflies have begun entering Mexico on their annual migration from the United States and Canada.

Mexico's Environment Department said Friday that the orange-and-black butterflies had been spotted by park rangers entering Coahuila state, on the border with Texas.

The butterflies head for the fir- and pine forest of central Mexico, where they spend the winter. No butterfly lives to make the full round trip, and it is unclear how they find the route each year.

Last year, butterflies that reached the wintering grounds covered 2.79 acres (1.13 hectares). That was a 69 percent rebound from the previous February's 1.65 acres (0.67 hectare), which was the lowest since record-keeping began in 1993.

The migratory route can be 3,400 miles (5,470 kilometers) long.