流浪的昆虫：帝王蝶

Teresa Fang

黑脉金斑蝶是北美地区最常见的一种蝴蝶，它体形较大，因而又有“帝王蝶”之称。这种蝴蝶每年都会进行大规模的迁徙，原因是什么呢？一起到文章中寻找答案吧！

Monarchs are the only butterflies known to make two?way migrations， as birds do. The annual migration of the eastern North American monarch butterfly is the most highly evolved （進化） of any known species of their kind. These butterflies can travel up to 3，000 miles in their short lifetime.

In the late summer and early fall， the butterflies typically leave southern Canada and northern and central regions of the United States. They make a dangerous trek （长途跋涉） to Florida and Mexico， where the weather is warmer. In recent years， monarch populations have been declining dramatically. In California， the population has decreased by 99.9%.

A monarch butterfly has four stages of life： egg， caterpillar （毛虫）， chrysalis （蛹）， and adult butterfly. No individual butterfly can make the entire migration， which may require four or more generations to complete. During their fall migration， the fourth generation of monarchs—known as the super generation—leave their summer breeding habitats and travel south to warmer places， where they can also find food and shelter.

But the future of these butterflies is in serious danger. The decline of the monarch population has been the consequence of habitat loss. Climate change and pesticides （杀虫剂） are causing harm， too. We must all work together to ensure the monarchs can find enough places with sources of food， shelter and water.

To help save the monarch butterfly population， teens in North Carolina community formed a club， which successfully applied for land for the monarchs' protection. Club members hope to secure more land from the community in the future.

Reading Check

What may cause the monarch population to decrease according to the text？