Monarch butterflies, the large orange-and-black insects,
黑脉金斑蝶——一种大型黑橙相间的昆虫
are a common summer sight in the northern United States and Canada.
夏季的时候在北美和加拿大十分常见。
They brighten in parks and gardens as they fly among the flowers.
当它们在花丛中翩翩起舞时，整个公园或花园都熠熠生辉。
What makes monarch butterflies particularly interesting is that they migrate,
黑脉金斑蝶有一点特别有趣，那就是它们会迁徙，
all the way to California or Mexico and back.
一直迁徙到加利福尼亚或墨西哥然后返回。
They are thought to be the only insect that does this.
人们认为它们是唯一一种会迁徙的昆虫。
Every year in the late summer, monarchs begin their migration to the south,
每年的夏季末，黑脉金斑蝶就开始向南迁徙，
those heading for Mexico go first for the Louisiana Mississippi region.
奔赴墨西哥的蝴蝶会先去路易斯安那州的密西西比地区。
Then they fly across to go for Mexico into Texas.
接着它们会飞往墨西哥进入德克萨斯州。
Once in Mexico, they establish themselves in one of about 15 sizes in the mountain forest.
一旦抵达墨西哥，它们会形成15只左右的小群体，在山林里定居。
Each side provides the winter home for millions of monarchs.
每一个地方都为数以百万计的黑脉金斑蝶提供了一个冬季的避难所。
The butterflies are so numerous that they often cover entire trees.
蝴蝶的数量十分庞大，常常覆盖树的整个表面。
When spring comes, they began their long journey north.
当春天来临时，它们又会开始漫长的向北迁徙之旅。
The question is often asked whether every butterfly makes the round trip journey every year.
经常有人问是否每只蝴蝶每年都这样迁飞于两地。
And the answer is no.
答案是否定的。
The average monarch lives about nine months.
黑脉金斑蝶的平均寿命只有9个月。
So when flying north, might lay eggs in Louisiana and die.
所以朝北飞时，它们可能会在路易斯安那州产卵并死亡。
The eggs of that generation may be found in Kentucky,
第二代蝴蝶的卵可能会在肯塔基州出现，
the eggs of the next generation may be in Wisconsin or Michigan.
第三代蝴蝶的卵可能产在威斯康星州或密歇根州。
The last generation of the season about the forth will make the journey back to Mexico and restart the cycle.
而当季最后一代，也就是第四代，它们会返回墨西哥并开始一个新的循环。
Scientists learn about monarch butterflies migration by capturing and placing identifying tags on the insects.
科学家们通过捕捉昆虫并在它们身上贴上身份标签的方式研究黑脉金斑蝶的迁徙。
By recapturing a tagged monarch and noting where it came from,
通过重新捕捉贴有标签的黑脉金斑蝶并标记它们的来源地，
the next scientist can figure out things like the butterfly's age and its routine.
下一位科学家就能推测出蝴蝶的年龄及其迁徙的路线。