The invasion has begun．Around the world，plants，animals，fungi ，and other life forms are moving into places where they don't belong．These attacks can mean major headaches for both wildlife and people．
For example，American white moths are damaging 1.5 million hectares of forests every year．And imported water hyacinth plants are choking some parts of the Yangtze River and the Pearl River．
However，sometimes it's not an accident．There was the boy from Hawaii who brought some snails to his grandmother in Miami．He thought that she would love them but，unfortunately，she didn't and threw them away．Scientists discovered the snails a year and a half later，after they had already pushed some native species close to extinction．It took seven years and a great deal of money to finally get rid of the invaders．
Humans have been moving species around for thousands of years．It started as people began migrating to new areas，bringing plants and animals with them．At that time，it was easy to control the danger of this as travel was still quite slow．
Words and Expressions
- fungi n．真菌，菌类
- moth n．蛾
water hyacinth［植］水葫芦
- migrate v．（使）移动；移居
Write an example of the effect of life forms moving into places where they don't belong．
Read the following sentence：
It took seven years and a great deal of money to finally get rid of the invaders．（人们花了7年的时间，耗费了大量资金才最终把它们消灭。）
It takes（sb．）some time to do sth．某人花……时间做某事
More examples：
It took me quite a long time to understand the meaning of the painting by Picasso．
Some scientists think that it will take hundreds of years to make robots do most work for humans．
Now please write your own sentences：
It took __________．
It will take __________．
恼人的物种迁移
物种入侵已经开始。在全世界范围内，动植物、真菌和其他的生命形式都在侵入本不属于他们的地方。对于野生动植物和人类而言，他们的入侵危害匪浅。
例如，每年有150万公顷的森林遭受美国白蛾之害。而引过的水葫芦正在淤塞长江和珠江的部分河段。
然而，有时物种入侵并非偶然。曾有个夏威夷的男孩把一些蜗牛带给他远在迈阿密的祖母。他以为祖母会喜欢它们，但不幸的是，她并不喜欢，把它们扔掉了。一年半之后，科学家发现了这种蜗牛，但那时它们已经快把当地一些物种推向灭绝的边缘。人们花了7年的时间，耗费了大量资金才最终把它们消灭。
人类迁移物种已经有上千年的历史了，这源于人们迁居到新的地方的同时，也把动植物带到了那里。在当时，因为旅行还比较慢，所以比较容易控制它们的危害。