Costs of invasive species

Since the first arrival of a rat by ship, we’ve known that invasions of alien species extract huge economic costs to society—seen in higher medical expenses, losses of crops to pests, and losses of native biodiversity that is unable to compete with invaders.  Examples are abundant, but the costs are rarely quantified.

Now a new study has attempted to estimate the economic costs of biological invasions worldwide, finding that over the past half-century, mosquitoes have extracted about $150 billion, rats about $67 billion, and feral cats about $52 billion from human coffers—an aggregate of $1.3 trillion.  Moreover, such invasions are likely to accelerate and have driven current costs up to $167 billion annually.

Some of these costs, for example, crops lost to pests, are recorded as damages.  Others are costs to manage the number and spread of invaders. Some, like the costs associated with mosquitoes that carry disease, have both a damage and management component.  Most of the invasions are of insects, but the invasion of natural ecosystems by feral domestic cats from the Middle East, extracts a toll on wildlife that impacts pursuits by ecotourists and sportsmen worldwide.  I’ve blogged about the impacts of feral cats before.  Now we know that cats extract the third largest economic cost among biological invaders.   See: (

Long-term studies have found invasive plants in 80% of the National Parks in the eastern U.S., such that these areas cannot now be thought to represent the undisturbed flora of North America.  These same areas have lost nearly all chestnut, elm, and increasingly ash to diseases and pests from other continents.

As quantified by these studies, managing to reduce the transport and arrival of alien species will not be cheap, but the costs of damages are estimated to be roughly 10X the cost of management.  We should applaud efforts by the U.S. Department of Agriculture to intercept potential pests and pathogens arriving in international shipments.  However, historical escapes of horticultural plants (e.g., Japanese barberry) and exotic pets from households (e.g., Burmese pythons in the Everglades) put some of the burden of prevention on each of us every day.



Diagne, C. and 8 others. 2021.  High and rising economic costs of biological invasions worldwide.  Nature 592: 571-576.

Lovett, G.M. et al. 2016. Nonnative forest insects and pathogens In the United States: Impacts and policy options. Ecological Applications 26: 1437 – 1455.

Miller, K.M. and 7 others. 2020. Long-term trends indicate that invasive plants are pervasive and increasing in eastern national parks.  Ecological Applications doi: 10.1002/eap.2239

One thought on “Costs of invasive species

  1. Another interesting essay. There is irony in the enforcement of ridding areas of invasive species. I once read that the early English colonists attempted to hunt foxes in the colonies, but discovered that the native gray fox could climb trees. So much for a gallop across field after field. I further read that the colonists then imported the red fox so that they could hunt. In New York State where I live, the Department of Environmental Conservation loves and protects the non-native red fox, but annually destroys the eggs and nests of a European variety of Swans which are ‘invasive’, though they have been here since the 1880’s.
    Aren’t honey bees and earth worms invasive species also? When does a species achieve ‘native status’?
    Or are “some animals are more equal than others.” With apologies to George Orwell.

    PS Then there is the sympathy factor. I have seen cat lovers intentionally feeding feral urban and suburban cats. Not to mention that leash laws for cats are almost never enforced. Ask any homeowner who owns a dog who looks out the window and barks at the local felines sauntering through the back yard.

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