Coldness triggers northward flight in monarch butterflies: Migration cycle may be vulnerable to global climate change

Each fall millions of monarch butterflies migrate south in order to escape frigid temperatures, traveling up to 2,000 miles to an overwintering site in a specific grove of fir trees in central Mexico. A new study suggests that exposure to coldness found in the microenvironment of the monarch's overwintering site triggers their return north every spring. Without this cold exposure, the monarch butterfly would continue flying south.

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