大象传媒

One species of butterfly has taken air travel to extremes. The monarch butterfly is the long-haul operator of the insect world. Monarchs flying around Canada in late summer are the great-great-grandchildren of monarchs that flew north in the spring. Triggered by shorter, cooler nights, they start to head south, flying the entire length of North America, and beyond. Finally, having flown three thousand miles, the monarchs reach their winter destination in the mountains of central Mexico. Somehow they find their way back to the same trees used by previous generations and millions cluster together for safety and warmth.