Pest Identification

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What’s Happening to the Monarch Butterfly?

The monarch butterfly is one of nature’s wonders. In North America, the appearances of the orange and black butterflies with white spots are a sure sign of summer. What’s truly amazing is every August the little insects with 4-inch wingspans migrate more than 2,500 miles from the United States and Canada way down to southwestern Mexico where the females lay eggs. Every winter, the oak, oyamel, and pine forests in the Mariposa Monarca Biosphere Reserve in Michoacán are so covered in monarchs you can barely see the trees beneath the swirl of wings.

In spring the migration is reversed but the butterflies returning to the north are second, third, and fourth generations of those that flew south. Monarchs only live two months and no individual makes the round trip, or even the entire journey north. Despite this fact, the monarchs return to the same migration spots year after year. How they do this remains a mystery but it might have something to do with the violet blue light spectrum or the earth’s magnetic field.

While the monarchs have engaged in their annual journey for countless millennia, the modern world is seriously encroaching on their migration. During the 2012-2013 season, the area occupied by monarchs at Mexican reserve dropped by 60 percent, resulting in only 3 acres. In 2014, monarch numbers dropped to the lowest level since record-keeping began in 1993.

Researchers blame a decline in the monarch’s favorite food, milkweed. In the Midwest, milkweed competes with corn and soy crops and is also toxic to cattle. Farmers have been working unsuccessfully to eliminate the weed from the fields for decades. But since the late 1990s new herbicides used with genetically engineered crops have reduced milkweed growth by two-thirds. This led to an 80 percent decline in monarch population in the Midwest between 1999 and 2010. And that’s only part of the problem.

Climate change has caused rising temperatures, severe droughts, and punishing floods in places where the butterflies feed and reproduce. Hot and dry conditions kill milkweed, reduce the capacity of adult monarch to mate, and destroy the eggs that are laid. Like other creatures facing extinction, monarchs are also loosing habitat to urban sprawl, logging, and other factors.

Monarchs have been known to fly thousands of miles over the ocean and they are becoming more common in Bermuda and even Great Britain and Australia. While they might not become extinct, they will certainly disappear from the Americas unless people in the United States and Mexico work together to preserve monarch habitat and encourage the planting of milkweed in gardens.