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Monarch Butterflies' Population Hits a Record Low

Mar 14, 2013 08:00 AM EDT

Researchers have said that the number of Monarch butterflies in Mexico has shrunk to its lowest ever in the past two decades, reports the Los Angeles Times. The most likely cause of this decrease in population size could be the loss of habitat of these butterflies, along with warm weather in the U.S.

Each year, the Monarch butterflies travel from the U.S. and Canada to Mexican forests, covering some 1,200 to 2,800 miles. The forests provide them with shelter during summer months, according to the World Wildlife Fund.

However, according to data from Mexico's National Commission of Natural Protected Areas, the forest area occupied by these butterflies has decreased from 50 acres to a mere 2.94 acres now, reports The New York Times. In December 2011, the area occupied by the butterflies was a little over 7 acres.

The number of monarch butterflies in Mexico has decreased by as much as 59 percent this year, which is the lowest ever in the past 20 years, The Associated Press reported. The numbers were estimated by a census that is conducted annually. The World Wildlife Fund is one of the sponsors for the census.

In recent years, the introduction of pesticides that kill the food source of the butterflies - milkweed - has also been seen as the reason behind their dwindling populations. "The decrease of Monarch butterflies ... probably is due to the negative effects of reduction in milkweed and extreme variation in the United States and Canada," the World Wildlife Fund and its partner organizations said in a statement, reports The Associated Press.

The Monarch butterflies begin life as an egg that hatch into larvae (which feed almost exclusively on the milkweed plant). These larvae become caterpillars and in the fourth stage they become butterflies. Only Monarchs born between late summer and early fall make the migration. Even though it takes about four generations of the Monarchs to make the incredible journey, each butterfly knows the way and at times, these butterflies have been found to come back to the same tree from where their great grandparents had begun the journey.

Craig Wilson, a senior research associate at Texas A&M University and a butterfly enthusiast, told USA TODAY that planting milkweed could provide habitat and food source for the larvae of the Monarch butterfly.

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