The number of monarch butterflies overwintering in Mexico increased 35% last winter, according to the World Wildlife Fund (WWF) and the National Commission of Natural Protected Areas (Conanp).

Monarchs, which migrate to Mexican annually from Canada and the United States, covered an area of 2.84 hectares in the pine and fir forests of México state and Michoacán in December, an increase of 0.74 hectares compared to the same month of 2020.

The WWF and Conanp said in a report that the increase was mainly due to repopulation efforts in the southern United States.

Jorge Rickards, general director of WWF México, said the increase was good news but highlighted that butterfly numbers were still well below those recorded three years ago.

“In 2018–19 the area the butterflies occupied to hibernate was 6.05 hectares, which indicates that we have to continue working to maintain this [upward] trend and strengthen the protection measures … [in] Mexico, the United States and Canada,” he told a press conference.

“Monarchs are important pollinators, and their migratory journey encourages reproduction … of flowering plants, which benefits other species … and contributes to the production of food for human consumption,” Rickards said.

The butterflies formed a total of 10 colonies in Mexico last winter, five in México state and five in Michoacán. Six were in the Monarch Butterfly Biosphere Reserve, an almost 60,000-hectare UNESCO World Heritage site that straddles the two states.

Some 186,000 people visited four different sanctuaries to observe the butterflies, Conanp said in a statement.

Environment Minister María Luisa Albores noted that a presidential decree ordering the elimination of glyphosate – a controversial herbicide – by 2024 will benefit the monarch butterflies that migrate annually to Mexico. The herbicide kills milkweed, the plant on which monarch butterflies lay their eggs, and the caterpillars eat milkweed leaves.

Illegal logging, a huge problem in Mexico, and climate change also pose a threat to monarch butterflies, which according to a Purépecha legend are the souls of dead children returning to their families.

With reports from Reforma