In many parts of the world, alien species are harming the environment and causing other problems. An alien species is a species plant or animal that has a new area. moved from its original home to Sometimes people have purposely introduced the new species; sometimes it arrives accidentally, as a side effect of international trade. In its new location, the alien species has no natural enemies, so it can grow and multiply without limit. Over time-sometimes decades, sometimes a few years the living new species takes and space and food away from the native plants animals. The result can mean drastic change in the natural landscape and problems for people. The tiger mosquito is an example of an alien species. This kind of mosquito is common in Asia, but in recent years it has moved to parts of southern Europe. Scientists of this believe that the eggs insect probably arrived inside some car tires that were filled with water. In a few years the mosquitoes multiplied and spread over large areas of Italy and other countries. Tiger mosquitoes can reproduce faster than the common European mosquito, so they quickly replaced a large percentage of the native mosquitoes. Though they do not cause serious disease in humans, tiger mosquitoes are a serious nuisance. They are far more aggressivethan common European mosquitoes, and the effects of their bites are kind of an Another example of a different continent i that has recently moved to another was first the zebra mussel. This small shellfish in the Great of North discovered Lakes America may have come from Russia on cargo ship. In a very few years, zebra mussels spread over all the Great Lakes and into many important rivers. They have grown into thick masses, covering many areas of lakes or river bottoms. They have also covered and closed up pipes of power stations and water treatment centers. Government officials say that mu have caused many millions of dollars worth of damage. Among the many examples of alien species o mammals that have caused damage is the Indian mongoose. This animal was brought to Hawaii in 1800s to kill rats in sugarcane fields. Since then they have grown in numbers that today they are a major threat to bird life on the islands. One of the mongoose's favorite foods, in fact, is birds' eggs Thus, the mongoose has caused millions of dollars worth of damage to poultry farmers in Hawaii, and it has greatly reduced the numbers of many nativ bird species. Many of these species, which are unique to the islands, are now at risk of extinction.