英语翻译一篇关于蝴蝶从美国向墨西哥迁移的文章有这么一句话：they fly across to go for Mexic

英语翻译
一篇关于蝴蝶从美国向墨西哥迁移的文章有这么一句话：they fly across to go for Mexico into Texas.怎么翻译啊?逻辑上有点乱,最好帮我把语法结构屡屡.

你这个句子是哪里看来的?是课本上的吧.to go for 加在这里莫名其妙嘛.请看原文：
Monarch butterflies are a common summer sight in the northern United States and Canada.
These large orange and black insects brighten parks and gardens as they fly lightly among the flowers.
What makes monarchs particularly interesting is that they migrate -all the way to California or Mexico
and back.They are thought to be the only insect that does this.
Every year in the late summer monarchs begin their journey to the south.Those heading for Mexico go first
for the Louisiana-Mississippi area,then fly across the Gulf of Mexico into Texas.Once in Mexico,they settle
themselves in one of about fifteen places in a mountain forest filled with fir trees.Each place provides a winter
home for millions of monarchs.The butterflies are so many that they often cover entire trees.When spring
comes,they begin their long journey north.
The question is often asked whether every butterfly makes the round-trip journey every year.And the answer
is no.The average monarch lives about nine months.So one flying north might lay eggs in Louisiana and then
die.The eggs of that generation may be found in Kentucky; the eggs of the next generation may end up in
Wisconsin or Michigan.The last generation of the season,about the fourth,will make their way back to Mexico
and restart the journey.
Scientists learn about monarchs' migration by catching and making marks on the insects.By recatching a
monarch with such a mark and noticing where it came from,the next scientist can get to know things like the
butterfly's age and its routing .
【Those heading for Mexico go first for the Louisiana-Mississippi area ,then fly across the Gulf of Mexico into Texas .目标方向墨西哥,首先进入路易斯安那-密西西比河地区,然后它们穿过墨西哥湾进入得克萨斯.】