Invasive species in the United States
Invasive species are a significant threat to many native habitats and species of the United States and a significant cost to agriculture and recreation. The term invasive species can refer to introduced or naturalized species, feral species, there are many species that are invasive. Some species, such as the dandelion, while non-native, do not cause significant economic or ecologic damage and are not widely considered as invasive. Overall, it is estimated that 50,000 non-native species have been introduced to the United States, including livestock, pets, economic damages associated with invasive species effects and control costs are estimated at $120 billion per year. S. Estimates for the damages caused by well-known species can vary as well, the Office of Technology Assessment has estimated zebra mussel economic effects at $300,000 a year, while an ACoE study put the number at $1 billion. Estimates of total yearly costs due to invasive species range from $1.1 billion per year to $137 billion per year, in 1993, the OTA estimated that a total of $100 million is invested annually in invasive species aquatic weed control in the US.
Introduced rats cause more than $19 billion per year in damages, exotic fish cause up to $5.4 billion annually, the total damage to the U. S. native bird population due to invasive species is approximately $17 billion per year. The federal government has promoted the introduction and widespread distribution of species that would become invasive, including multiflora rose, kudzu. Before the 20th century, numerous species were imported and released without government oversight, such as the gypsy moth, over 50% of flora recognized as invasive or noxious weeds were deliberately introduced to the United States, by either government policy or individuals. Current government policy can be separated into two categories, preventing entry of a potential invasive species and controlling the spread of species already present. This is carried out by different government agencies, depending on types of damage a species can cause. The Lacey Act gives the FWS the power to list a species as injurious, the Alien Species Prevention and Enforcement Act of 1992 makes it illegal to transport a plant or animal deemed injurious into the United States through the mail.
The FWS concerns itself mostly with the species likely to threaten sensitive habitats or endangered species. The USDA is involved in preventing the introduction of species, largely through the Animal and Plant Health Inspection Service. APHIS enforces bans against interstate transport of pests, diseases, an example of the USDA banning imports is the ban on fresh mangosteen fruit due to concerns about fruit flies from southeast Asia. This ban originally allowed only frozen or canned fruit, but now allows for fresh irradiated fruit to enter, many invasive species are spread inadvertently by human activities, such as seeds stuck to clothing or mud transporting firewood, or through ballast water. The government has instituted several different policies related to different pathways the invasive species may be spread. For example, quarantines on a federal and state level exist for firewood across the Eastern United States in an attempt to halt the spread of the ash borer, gypsy moth, oak wilt