Introduction

Invasive Species Defined

What's Being Done

 National Invasive Species Information Center

Submodule 7: The Price We Pay -- Economic Impacts

Monetary Costs of Invasive Species

Economists and other researchers have used several methods in an attempt to estimate the costs of invasive species. Presented below are some examples:

Plants – It is estimated that there are over 25,000 non-indigenous plants have escaped cultivation and become established in U.S. ecosystems. In the 1990s, such weeds cost the U.S. economy about $20 billion for herbicides, mechanical control, and other management practices. Costs to control weeds for major crops and animal health were as high as $15 billion. Most of the rest of the cost was for weed management on golf courses, forests, aquatic areas, and other non-crop sites. The value of losses for these sites is generally not calculated, so it is not part of the $20 billion figure.

Fish – Invasive fish are estimated to cost about $6 billion annually in the U.S. (although this estimate varies considerably depending on whether the value of introduced fish to the sport fishing industry is included or not). As of 1997, there were 138 species of non-indigenous fish established in the country, most found in states with mild climates like Hawaii, California, and Florida. Invasive fish negatively change aquatic ecosystems by, for example, increasing the water’s turbidity or reducing native vegetation. In addition, exotic fish sometimes hybridize with natives, diluting the genetic integrity of both involved species.

Birds – About 10% of the bird species in the U.S. were introduced into the country. About 95% of these bird additions are considered detrimental because they damage property and crops, and spread disease; but introduced species can be beneficial…like chickens! The common pigeon (Columba livia) is probably the most notorious invasive bird because of its sheer numbers. This bird dirties structures, feeds on valuable crops, and carries and spreads over 50 known diseases. It has been estimated that pigeon control alone costs over $1 billion annually.

Mammals – Several species of domestic animals including pets and livestock have escaped into the wild and become invasive. These include dogs, burros, pigs, and deer, and are responsible for problems like habitat destruction and eating native plants to the point of extinction. Invasive mammals also destroy populations of native animals. For example, feral cats are responsible for the death of millions of birds and countless amphibians and small mammals. The most numerous invasive mammals are no doubt rodents, primarily rats and mice. While many rodent species are native, several dangerous and detrimental species were imported from all over the world. Some estimates as of 2004 published by the USDA for cost of invasive mammals include:

• Horses (Equus caballus) and burros (Equus asinus) introduced into western states cost about $22 million annually
• Feral pigs (Sus scrofa) cause damage nationwide of about $800 million/year
• Feral dogs (Canis lupus) cause about $9-10 million in losses to cattle and sheep each year
• Feral cats (Felis silvestris) kill about 465 million birds per year at an estimated cost of $14 billion
• Nutria (Myocastor coypus) cost over $6 million per year in damage to sugarcane
• Rat (Rattus rattus) destruction of stored grains in the U.S. averages more than $19 billion per year

Mollusks – These invertebrates are aquatic organisms that often arrive in the U.S. in ship ballast water. Two particularly important offenders are the zebra mussel (Dreissena polymorpha) and the Asian clam (Corbicula fluminea), which clog waterways and decrease populations of native aquatic species. The zebra mussel is expected to invade most bodies of fresh water in the U.S. by about 2020, and is already estimated to cost $5 billion/year for control and repairs due to infestations. Control of the Asian clam is estimated to cost $1 billion annually. On the west coast, a new invader to San Francisco Bay is the shipworm (Teredo navalis), a mollusk estimated to cost $200 million annually for control and containment.

Insects and other arthropods – By far the largest group of invasive species, approximately 4,500 arthropods have been introduced into the U.S. Invasive insects are known to wipe out entire populations of native species, for example, the balsam woolly adelgid (Adelges piceae), is estimated to have destroyed up to 95% of the Fraser fir (Abies fraseri) in the southern Appalachians. The adelgid also infects the more valuable balsam fir (Abies balsamea), which grows in the northeastern U.S. Both trees are valued as Christmas trees and monetary losses to the industry have been substantial. The southern part of the country has been particularly hard hit by invasive insects that are not only expensive to control but also cause huge financial losses by their infestations. The red imported fire ant (Solenopsis invicta) kills livestock and these costs, along with control expenses, are estimated to be $1 billion/year. In addition, the introduced Formosan termite (Coptotermes formosanus) inflicts structural damages that, coupled with efforts to control the pest, incur costs of nearly $1 billion annually.