Invasive Species: Animal, Vegetable or Political? by Dana Joel Gattuso

“These are like something from a bad, horror movie.”
-Former U.S. Secretary of Interior Gail Norton, Time for Kids, October 2002

What do mute swans, kudzu, red clover, pigs, and starlings have in common?  Not much, except that they are all non-indigenous species – that is, the species does not originate from within the United States.

And that is essentially all they have in common.  Yet many government agencies, lawmakers and environmental special-interest groups would like to clump together the thousands of these species introduced within our borders and stamp out their existence.  More than 50 bills are pending in the U.S. Congress to address so called “invasive species.”1  Most bills would expand federal authority to further control land use and authorize billions of tax dollars to eradicate non-native flora and fauna.

Some “exotic species” are problematic, overtaking other species and imposing large economic costs in damages.  But, contrary to public perception, these are more the exception than the rule.  Most non-native species adapt to their surroundings, and many are even useful.

Legislation should be narrow in scope, case-specific, and based on science to control the spread of those that truly are destructive.  The “invasive species” bills pending in Congress are not based on science but rather assume all non-indigenous species are harmful unless proven otherwise.  Most of the bills would create massive government bureaucracies and, worse, grant federal agencies greater authority to regulate lands and waters, public or private, where these species exist.

Some experts warn legislation that defines “invasive species” so broadly and directs government agencies to “control” invasives on private as well as public lands could lead to a massive erosion of property rights.  According to Senate Environment and Public Works Committee Chairman James Inhofe (R-OK), “Bills of this scope and volume deserve close scrutiny because they can easily spiral into a regulatory morass.  As the dysfunctional Endangered Species Act has shown, Congress should be very wary of how legislation on invasive species is drafted.”2


No one knows for sure how many nonnative species exist in the United States. Documented estimates range from 6,500 by the U.S. Geological Survey3 to 50,000 from Cornell University.4  Still others assert these estimates are low because they don’t include the numerous foreign species that are unknown.5

One may wonder why the effort to quantify exotic species given that just about all plants and animals, including the many we eat, grow in gardens and even keep as pets, hail from other parts of the world.  The fact is that out of all the non-indigenous species found in the United States, only a tiny fraction are problematic.  Out of these, “problematic” largely constitutes economic damage from clogged water pipes from aquatic foreign species, economic costs imposed on some commercial industries such as tourism and commercial or recreational fishing and costs to farmers for damage from nonnative pests.

Yet many policy leaders and conservation activists lump all introduced species together and portray them as one of the biggest environmental crises of our lifetime.  The National Park Service calls non-natives “one of the greatest threats to our natural and cultural heritage;” the Union of Concerned Scientists considers the intruders “one of the most serious and least-recognized tragedies of our time” and NASA calls them “the single most formidable threat of natural disaster of the 21st century.”6

There are currently 28 laws that pertain to the “control” of exotic species. The most recent – and far-reaching – is Executive Order 13112 on Invasive Species, signed by President Clinton in 1999.  The rule revoked an existing executive order signed by President Carter that forbids the introduction of invasive species into U.S. ecosystems under federal authority.

The newer order granted new powers to federal authorities in an effort to wipe out not just foreign pests imposing economic damage but all “invasive species.”  The new, broader definition establishes that an “invasive species” is any “alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.”7  Federal agencies were granted new, expansive authorities that can be applied to private as well as public lands to control and “minimize” species impacts and restore local species and their habitat to affected ecosystems. 

The executive order also created the Invasive Species Council to monitor invasives’ impact, develop a network for information sharing among government agencies, and come up with recommendations for eradicating the species or “preventing their spread.”  Under the order and other laws, more than 20 government agencies are responsible for some aspect of invasive species “management,” with seven agencies – including the Department of Defense – spending over $1 billion a year.8

Given that the executive order’s revised definition of invasives covers just about every known species, it is no surprise that these demons are attributed with a wide range of crimes, including not only clogged pipes, power outages and agriculture disturbances but also spread of disease, collapse of buildings, threat to the world’s ecosystems and even the “leading cause of extinction worldwide.”9  Estimates on the amount of damages amounts to anywhere from $100 billion to $200 billion a year.10

Hype and Hyperbole Over “Invading Aliens”

Some invasives, to be sure, are destructive, imposing high economic costs on numerous commercial industries.  Farmers face myriad non-indigenous pests, for example, and the worst of them, like crop weeds, rats, gypsy moths and Mediterranean fruit flies, can imperil crops and jack up food prices.  Aquatic non-indigenous species that can out-compete small-mouth bass, trout and other fish populations are hurting both the commercial and recreational fishing industries, particularly in the Great Lakes region.  Forests are prey to many foreign predators, including the Asian longhorn beetle and gypsy moth.  And a vast assortment of invaders in Hawaii impact tourism, agriculture, and fishing industries.

The same can be said of native species that proliferate and easily evolve outside their natural habitat.  Most are harmless and even beneficial while some can wreak costly havoc, such as rabbits, white-tailed deer, barnacles and even native tics that can carry disease.

The well-kept secret about exotic species is that cases of destruction are the exception; most non-indigenous species are benign. As a report by the Congressional Research Service states: “While the damage from some non-native species can be great, few have proved to be economically harmful, and many are beneficial.”11

In short, most of the costs imposed from a small percentage of non-native species affect select businesses and industries.  They are not the national calamity portrayed by the many interest groups that benefit from tax dollars and expanded government authority on lands where non-natives are found.

Not All Snakeheads

Many invasives were brought here intentionally, despite the billions of tax dollars now spent to keep them out.  Kudzu, nicknamed “the vine that ate the South,” was brought to the region to control soil erosion.  European starlings were brought here in 1890 by a Shakespeare-enthusiast to introduce bird species ever mentioned by the Bard to the United States.12  Asian carp, prevalent in the Mississippi River Basin and the target of numerous federal and state regulatory bills, were brought here in the 1960s and 1970s to control algae throughout the South’s lakes and ponds.

Rarely mentioned are the numerous industries that rely on non-indigenous species, including nurseries, aquaculture, and exotic pets.13  Moreover, numerous states honor non-native species as their State Flower or State Birds.  Vermont’s red clover, Maryland’s black-eyed Susan, California’s poppy and South Dakota’s ring-necked pheasant are all “invasive” species.

The wide range of benefits from many “invasives” is both well-documented and under-reported.  Asian oysters, for example, are better at filtering out water pollutants than native oysters.  They also grow faster and withstand disease better than natives.  Biologists are currently considering releasing the mollusk in the Chesapeake Bay to help restore oyster stocks and clean up the bay’s pollution.  A recent study by the Johns Hopkins School of Public Health found the Asian oyster could significantly benefit the bay’s deteriorating water quality.14

In fact, invasives have become such a common part of our environment, culture and even diet that we don’t think about them.  For example, soybeans, kiwi fruit, wheat and all cattle except the turkey are exotic species.  Collectively, nonnative crops and livestock comprise 98 percent of our food system.15  These and other benefits from invasives are so vast that, according to the Congressional Research Service, they probably exceed the costs.16  Regrettably, benefits are rarely considered in reports and studies on the species’ impact; nor are benefits much reported in news stories and articles on non-indigenous species.

The zebra mussel, for example, is one of the most feared “invasives,” referenced in almost any article on exotic species and the purported raison d’etre for numerous bills pending in the U.S. Congress and state legislatures.  The tiny mollusk inhabits fresh water lakes and rivers and is infamous for clogging industrial plant water pipes, particularly in the Great Lakes and Mississippi Basin, where they have exploded on the scene.  Believed by scientists to have been brought over from Europe in ships’ ballast waters, some observers claim these hardy, prolific shell-fish could wipe out native aquatic life, though there is no conclusive evidence to support this theory.17

Rarely reported is the zebra mussel’s positive effect on water quality.  These “filter feeders” eat algae and fertilizer runoff from lakes and, as a result, waters they populate are frequently clear and free of pollution.  As reported by the U.S. Geological Survey:

“…there has been a striking difference in water clarity improving dramatically in Lake Erie, sometimes four to six times what it was before the arrival of zebra mussels.  With this increase in water clarity, more light is able to penetrate deeper allowing for an increase in aquatic plants. Some of these macrophyte beds have not been seen for many decades due to changing conditions of the lake mostly due to pollution.  The macrophyte beds that have returned are providing cover and acting as nurseries for some species of fish.”18

The plant purple loosestrife, maligned for crowding out natural wetlands vegetation and wildlife, has been called everything from “the poster child” for invasive species19 to the “purple plague.”20  Yet there is no scientific evidence that the plant causes actual displacement in the life cycle of native flora or fauna.21  Moreover, some biologists acknowledge actual benefits, including the plant’s ability to absorb nitrogen and phosphorus from the water better than even cattails and to help prevent soil erosion.22

Similarly, the South American water hyacinth blankets lakes and ponds in tropical climates, halting boat activity and, some claim, depleting aquatic life by blocking sunlight and crowding out native plant life.  But the plant also has a newly discovered talent – it eats raw sewage.  The alien species is used by a growing number of sewage treatment plants around the country23 to help purify water and performs the job at a fraction of the cost of conventional methods.  NASA, which is researching the new-found technology, planted water hyacinth over 40 acres of sewage lagoons and reports: “The plants flourished on the sewage and the once-noxious test area became a clean aquatic flower garden.”  They are also being researched for fertilizer, animal feed and biofuel.24

Threat to Biodiversity?

Among the exaggerated claims regarding non-indigenous species is their alleged threat to the variety of species within ecosystems.   According to Defenders of Wildlife, “The spread of non-native or ‘exotic’ species has emerged in recent years as one of the most serious threats to biodiversity, undermining the ecological integrity of many native habitats and pushing some rare species to the edge of extinction.”25  The Nature Conservancy lists invasives second, just after species’ habitat loss, as the biggest danger to biodiversity.26

To be sure, there are cases where exotic species have eliminated local flora and fauna, out-competing them for food, oxygen or sunlight; the same can be said of some resilient native species too.  But there is no scientific evidence of actual global extinction caused by a non-native species.  Nor do exotic species threaten species “richness” or “biodiversity.”27 

In fact, some scientists believe non-natives enhance diversity.  According to Michael Rosenzweig, a biologist at the University of Arizona and the editor of Evolutionary Ecology Research, the presence of exotic species can actually lead over time to a greater number of species because the destruction of local species would allow for the introduction of new species.28  Similarly, evolutionary biologist Gereet Vermeij wrote in Science, “Invasion usually results in the enrichment of biotas [plant and animal life of a particular region] of continents and oceans.  In some biotas… interchange has pushed diversity to levels higher than the pre-extinction number of species.”29

Where’s the Science?

Xenophobia – an unfortunate tendency of some unthinking humans to dislike things foreign – has given non-native plants and animals a bad name.  The media, some researchers, and environmental interest-groups are largely to blame, raising the level of hysteria by playing on public fears with articles and books that evoke images of attacking aliens that, left unchecked, will multiply and conquer life as we know it.

Consider typical headings: “Giant rats invade Florida Keys: 9-pound rodents could threaten native species,” “Sironga swamp threatened as ‘magic tree’ swallows up rivers,” and “Killer Algae.”30  Not surprisingly, emotion rather than science is driving government policy over how to handle these feared aliens.31  Missing from the debate are questions like: Is this a serious problem that extends beyond disruptions for some commercial industries?  What are the benefits of non-indigenous species, and how do they stack up against the costs?  What are the costs of widespread intervention, and is it justified?  Who are the real players behind the “invasive species” hysteria, and how do they benefit from government regulations and intrusion?

Furthermore, existing laws and pending legislation apply the flawed, better-safe-than-sorry “precautionary principle,” holding that we should first assume all invasives are damaging until we prove otherwise even though only a small percent of non-native species cause significant damage.

Legislation: Washington Goes to War

In spite of the fact that most non-native species are harmless, lawmakers are reacting to hype and exaggerations, launching numerous bills that, if passed, would cost taxpayers billions of dollars, assign government agencies a host of responsibilities aimed at eradicating “invasives” and preventing their spread, and expand government’s authority over land use control.  Consider:

*     S. 770, the National Aquatic Invasive Species Act of 2005: The bill, according to its sponsor, Senator Carl Levin (D-MI), is a “comprehensive approach towards addressing aquatic nuisance species.”32  It attempts to prevent the introduction of aquatic invasives into the United States, screen all species entering intentionally, launch a national system for identifying introduced non-natives, establish a “rapid response” fund within the U.S. Treasury to aid states and non-government organizations (NGOs) that have detected a non-native “emergency” and earmark $30 million a year for “research, education and outreach.”33

The bill reads more like a plan to prepare the nation for an apocalyptic attack from aliens than to prevent damage from fingernail-sized mussels and waterweeds.  Homeland Security would be given new authority to police vessels’ ballast waters, side-tracking the agency’s focus on terrorists to cover a very different class of invader.

“Aquatic” refers not just to oceans and lakes but to tributaries, wetlands, riverbanks and creeks – on private as well as public lands.  The bill also applies the “precautionary principle,” requiring the Fish and Wildlife Service to prove the species is not harmful if it determines to take no action.  Moreover, the meaning of harmful is expanded to apply to change in the “structure and functions of ecosystems.”34

States would receive $30 million a year to battle their wars with invasives, including those that don’t have a notable problem with non-indigenous species.  Co-sponsor Senator Susan Collins (R-ME) made a strong plea to save the “lakes and ponds… under attack” in her state of Maine,35 although the Congressional Research Service lists Maine among the states having “relatively few non-natives.”36

S.770 was introduced in 2005 and is pending in the Senate Committee on Environment and Public Works.

*     S. 1541, Public Land Protection and Conservation Act of 2005: S.1541, sponsored by Senator Daniel Akaka of Hawaii, appears innocuous at first glance, providing “cost-shared grants” to “appropriate public or private entities and Indian tribes” to “protect, enhance, restore and manage public land and adjacent land through the control of invasive species.”  It would provide funds to states to “identify” invasives in their state,” “assess needs to restore” native ecosystems and establish “rapid response capability.”  It also would fund private entities to “encourage increased private sector involvement.”

In practice, the bill would expand its army of crusaders, rewarding states, localities, Indian tribes and environmental interest groups with $250 million a year for “combat[ing] incipient invasive species invasions.” And it would lure private landowners with monetary incentives to assist in the effort, setting the stage for increased government involvement in land use on private property.

Furthermore, this legislation would be a costly expansion of current law; federal agencies already are directed to carry out many of the responsibilities outlined in the bill, including providing grants to states to “control” non-native species.  Scott Cameron, deputy assistant secretary at the Department of Interior, testified that “all of the actions called for [in the bill] can be achieved within existing authorities” and that his agency “cannot support… the sizeable authorization levels contained in this legislation.”

S. 1541 was introduced July 2005 and is pending in the Senate Energy and Natural Resources Subcommittee on Public Lands and Forests.

*     S. 2545, Great Lakes Collaboration Implementation Act: This bill sponsored by Senators Mike DeWine (R-OH) and Carl Levin (D-MI) authorizes $13 billion in restoration projects to the Great Lakes region, including $11.25 million a year to combat aquatic invasives.  It reauthorizes and expands the 1996 National Invasive Species Act, requiring all vessels entering the Great Lakes region to follow a ballast water “management” program and install “best performing treatment technology.” It also would mandate the screening of all invasive species entering the country intentionally, and set up a new nationwide invasives monitoring and rapid response system similar to that in S.770.

Moreover, the bill calls for the federal government to complete, fund and operate a costly electric barrier to block Asian carp’s entry into the Great Lakes from the Mississippi River Basin, a provision to gratify the region’s multibillion dollar sport fishing industry.  The barrier is estimated to cost $6 million to complete and $20,000 a month to operate.37

S. 2545 was introduced April 2006 and is pending in the Senate Committee on Environment and Public Works.


The key problem with government’s handling of the issue of non-natives is that it takes a simplistic view, bundling all the species together and exaggerating their effects on ecosystems and commercialism; if they come from outside our borders, we must assume they are harmful until we have evidence to prove otherwise.  Resulting legislation such as those referenced above grant government sweeping authority, threaten property rights and authorize billions of taxpayer dollars when the actual problem is a small number of non-native species that impact the economic interests of some commercial industries.

Like snowflakes, no two species are alike.  As stated by Mark Davis, an expert on invasives at Macalester College in St. Paul, Minnesota, “There are not generic conclusions we can make about invasive species.  Each species really has to be approached uniquely.”38  Furthermore, species’ relationship within an eco-system is extremely complex and can vary enormously from one ecosystem to another.  To address these unique circumstances, legislation should be case-specific, weigh species’ benefits against costs, and should be based on peer-reviewed scientific evidence.

Dana Joel Gattuso is a senior fellow at The National Center for Public Policy Research in Washington, D.C.  


1 U.S. Library of Congress, “THOMAS,” at

2 Also, see R.J. Smith: “This could expand the federal government’s power far beyond what the Endangered Species Act has done. Few people have endangered species on their land. Almost everyone has non-native species.” Joseph A. D’Agostino, “Decreasing Invasive Species May Increase Invasive Government,” Human Events, May 10, 2003.

3 U.S. Department of Interior, U.S. Geological Survey, National Invasive Species Information Center, at

4 David Pimentel, Lori Lach, Rodolfo Zuniga, and Doug Morrison, Environmental and Economic Costs Associated with Non-Indigenous Species in the United States, College of Agriculture and Life Sciences, Cornell University (Ithaca, New York), June 12, 1999.

5 M. Lynne Corn, Eugene H. Buck, Jean Rawson and Eric Fischer, “Harmful Non-Native Species: Issues for Congress,” CRS Report for Congress, U.S. Congressional Research Service; Resources, Science, and Industry Division, Washington, D.C., April 8, 1999, available at as of July 17, 2006.

6 Statement of Michael Soukup, Associate Director for Natural Resource Stewardship and Science, National Park Service, Department of the Interior, before the Subcommittee on National Parks, U.S. Senate Committee on Energy and Natural Resources, August 9, 2005; “Invasive Species: Scientists Demand Action on Invasive Species,” Union of Concerned Scientists, Cambridge Massachusetts, January 18, 2006 (last revised), available at as of July 17, 2006;, Invasive Species Management, Program Plan: 2003-2007, NASA, Office of Earth Science, Applications Program, June 6, 2003.

7 Executive Order 13112 of February 3, 1999, Federal Register, Vol. 64, No. 25, February 8, 1999.

8 “Invasive Species: Clearer Focus and Greater Commitment Needed to Effectively Manage the Problem,” Report to Executive Agency Officials, GAO-03-1, U.S. General Accounting Office, Washington, D.C., October 2002, p. 8.

9 Corn; Tim Johnson, “Invasive Species,” The Burlington Free Press, November 9, 2003.

10 Invasive Species Management; Pimentel.  In this report, the researchers estimate cost of environmental damages of $137 billion a year.

11 Corn.

12 Chad Cohen, “Bioinvasion: From Old World to New,” National Geographic News, National Geographic, January 23, 2001, available at as of July 17, 2006.

13 Corn.

14 Tom Pelton, Baltimore Sun, May 26, 2006.

15 Pimentel.

16 Corn.

17 While inconclusive, some studies conclude that zebra mussels could have a negative impact on native mussel populations. However, studies on their impact in the Great Lakes show that “zebra mussels are having a minimal effect on fish populations.” Greg Linder, Ed Little, Lynne Johnson, and Chad Vishy, Risk and Consequence Analysis Focused on Biota Transfers Potentially Associated with Surface Water Diversions Between the Missouri River and Red River Basins: Appendices, U.S. Geological Survey, Biological Resources Division, Columbia Environmental Research Center (Columbia, Missouri) Appendix 3A, July 2005, pp. 7-8.

18 Ibid, p. 8.

19 Johnson.

20 “Purple Loosestrife,” Invasive Species Initiative, The Nature Conservancy, Arlington, Virginia, available at as of July 17, 2006.

21 Heather A. Hager and Karen D. McCoy, “The Implications of Accepting Untested Hypotheses: A Review of the Effects of Purple Loosestrife (Lythrum Salicaria) in North America,” Biodiversity and Conservation 7, pp. 1069-1079, 1998; Sarah Stackpoole, Purple Loosestrife in Michigan: Biology, Ecology, and Management, National Sea Grant, National Oceanic and Atmospheric Administration, Silver Spring, Maryland , pp. 2-3, 2004, available at as of July 17, 2006.

22 Johnson.

23 Among those communities using the plant to treat water sewage are Rio Hondo, Texas; Orange Grove, Mississippi; Walt Disney World, Florida and San Diego, California; “Success at Stennis: A New Image for the Water Hyacinth,” Technology Development & Transfer Office, Stennis Space Center, NASA, available at as of July 17, 2006.

24 Ibid.

25 “Invasive Species,” The Biodiversity Partnership, Defenders of Wildlife, Washington, D.C., May 12, 2006 (last revised), available at as of July 17, 2006.

26 “Combating Invasive Species,” The Nature Conservancy, Arlington, Virginia, available at as of July 17, 2006.

27 Even the United Nation’s Convention on Biological Diversity’s Subsidiary Body concluded in their report on invasive species, “there are no records of global extinction of a continental species as a result of invasive species…” Convention on Biological Diversity, Subsidiary Body on Scientific, Technical and Technological Advice, Development of Guiding Principles for the Prevention of Impacts of Alien Species by Identifying Priority Areas of Work on Isolated Ecosystems and by Evaluating and Giving Recommendations for the Further Development of the Global Invasive Species Programme, Fourth Meeting, Montreal, Canada, June 21-25, 1999.

27 John Newcomb, “Alien Species Often Fit in Fine, Some Scientists Contend,” New York Times, September 4, 2001; James H. Brown, Department of Biology, University of New Mexico and Dov F. Sax, Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, “An Essay on Some Topics Concerning Invasive Species,” Austral Ecology, Vol. 29, p. 534: “losses due to extinction of native species have on average been more than offset by the colonization of invading species. Already abundant and widespread species have expanded their ranges, more than compensating in local richness for the restricted endemic forms that have disappeared.”

28 Ibid.

29 Geerat J. Vermeij, “When Biotas Meet: Understanding Biotic Interchange,” Science, September 6, 1991, Vol. 253, Issue 5024; Ronald Bailey, “Bio-Invaders: Are We Under Attack by ‘Non-native’ Species?  Should We Care?” Reason, August/September 2000.

30 Paul H. Gobster, “Invasive Species as Ecological Threat: Is Restoration an Alternative to Fear-Based Resource Management,” Ecological Restoration, (University of Wisconsin), Vol. 23, Issue 4, December 2005, p. 262.

31 Brown.

32 Senator Carl Levin, Introductory Remarks before the U.S. Senate Committee on Environment and Public Works, U.S. Senate, Washington, D.C., April 13, 2005.
33 U.S. Library of Congress, THOMAS, S.770, “National Aquatic Invasive Species Act of 2005,” April 13, 2006; Senator Susan Collins, Introductory Remarks before the U.S. Senate Committee on Environment and Public Works, U.S. Senate, Washington, D.C., April 13, 2005.

34 Julie Kay Smithson, “‘Invasive Species’ Report,” Property Rights Research, March 1, 2006, available at as of July 17, 2006.

35 Senator Collins.

36  Corn.

37 Dan Egan, “Carp Barrier May Prove Vulnerable,” Milwaukee Journal Sentinel, April 26, 2006; Dan Egan, “Carp Barrier Delayed: Device Sending Too Much Electricity Too Far Down Canal, Posing Danger to Barges,” Milwaukee Journal Sentinel, May 5, 2006.

38 April Reese, “Invasive Species: Effects of Introduced Organisms Overstate, Some Researchers Say,” Land Letter, E&E Publishing, LLC, September 22, 2005.

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