Monarch butterflies, with their distinct orange, black and white wings, are considered the king of butterflies but they are also proving to be masters of survival.

A cold snap a few days ago in the mountains west of Mexico City, where millions of these gather to spend the winter, failed to kill them. Last Friday, the monarchs were seen alive and well (left) at the Ocampo community, in Michoacan state, Mexico.

Activists said they were concerned about the unusual cold weather because heavy rain and bitter cold in 2001 killed millions of monarchs at this reserve.

Monarch butterflies are not able to survive the cold winters in most parts of the United States so they migrate south and west to places such as Mexico, around October, to escape the cold weather.

They make journeys of about 4,000km or more annually during their migration. They start the return trip to the US in March, and arrive around July.

This year, the butterflies covered a total area of about 4ha, compared with 1.13ha in 2014 and a record low of 0.67ha in 2013.

The figures suggest the numbers of these butterflies may be rebounding, although 20 years ago, they covered as much as 18ha.