Invasives Blog

farmer on an ipad
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The total cost of invasive species in the United States is estimated to be in the order of billions each year, according to a recent study.

The study, which is currently published as a preprint on BioRxiv, also estimates the total invasive species cost over the past 60 years to be at least $1 trillion, when considering highly reliable reports only. This figure reaches around $4.5 trillion when all data are included.

The challenge

Economic losses from natural causes such as pests, diseases or invasions are notoriously difficult to measure on a large scale, with few researchers willing to take on the challenge – the last estimate of the cost of invasive species in the US was published in 2005. Since then, many more invasive species have entered the country despite efforts to prevent new invasions, and economic costs have risen substantially. A fresh estimate is therefore urgently needed to help inform US policymakers’ decisions on how best to tackle biological invasions, and to highlight the full extent of the damage caused by invasive species to the general public.

Cost of invasive species: Invacost project

An estimate of this scale was was made possible thanks to the Invacost project. Funded by the French National Research Agency and BNP-Paribas Foundation Climate Initiative, the Invacost project involved the construction of a global database of reported costs of invasive species, using data derived from structured literature reviews and consultations with invasive species experts. The Invacost database has already been used to estimate the economic costs of invasive species in a number of other countries and geographic regions, some of which have been published in a special issue of the journal Neobiota.

Using statistical computing software to interrogate the US data, the authors were able to explore how costs changed over time and across different geographic regions, industry sectors and species. Agriculture suffered the largest losses at over $500 billion, followed by the environmental, forestry, and public and social welfare sectors. The total annual cost showed a 10-fold increase from 1960-1969 to 2010-2020, from an average of $2 billion to $20 billion per year. This reflects the transition to intensive farming practices over the past 50 years, which while boosting agricultural productivity, has also enabled pests to thrive.

Most costly species

Invasive species cats
Cats are the most costly invasive species in the US
Image by Fabio Grandis from Pixabay

Although a number of agricultural pests featured in the top 10 most costly invaders, domestic and feral cats (Felis catus) took first place with estimated costs of $45.5 billion, followed by black rats (Rattus rattus) at $23.8 billion. Cats predate on native wildlife, in particular birds, while rats cause damage by eating crops and stored grain, outcompeting native species and vectoring diseases. Both of these species are widespread across all regions of the US, which may explain their high costs at the national scale.

Formosan termites (Coptotermes formosanus) took third place at an estimated $18.5 billion. With their voracious appetite for wood, Formosan termites can damage trees, homes, telephone poles and railway tracks, and have been known to chew through plastic, concrete and even metal in their search for food, sometimes causing regional power cuts as they chew through underground power lines.

Two species of fire ant, Wasmannia auropunctata and Solenopsis invicta, also made the top 10. Like termites, fire ants can damage electrical equipment such as agricultural machinery, as well as harming crops and native biodiversity by tunnelling through roots and stems, eating seeds and disturbing pollinators.

Accuracy of the estimates

Red swamp crayfish
A red swamp crayfish
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The authors noted a number of limitations to the accuracy of the estimates, such as reporting bias. It is no coincidence that the two most economically damaging species, rats and cats, are also among the most recognisable to the general public. Well-known species which live among humans are much more likely to draw research attention. No estimates were available for the majority of invasive species, in particular aquatic invasives, potentially reflecting a broader reporting bias across environmental economic research. There also appears to be a divide between economists and ecologists in terms of species prioritisation, as several species, such as the red swamp crayfish (Procambarus clarkii) and Amur Honeysuckle (Lonicera maackii) feature among the most studied ecologically in the US, but have few, if any, economic estimates available.

There were various other potential sources of missing costs – for example, effects on ecosystem services, which are more difficult to measure. Given these limitations, the authors advised that all figures should be interpreted as the most inclusive minimum estimates available, and are subject to change as the Invacost database evolves over time.

Cost of invasive species: study’s implications

This study could have major implications for the US government’s spending on invasive species management. Currently only $1.35 billion, or 1% of a total $199 billion, is spent on biosecurity to prevent new invasions. With climate change and global trade intensifying, the threat of new invasions is only expected to loom larger. Greater investment in biosecurity is therefore clearly needed to contain the rapidly expanding costs of damage caused by invasive species.

CABI products and tools

CABI’s Invasive Species Compendium provides free access to data on over 800,000 invasive and potentially invasive species, as well as abstracts and full text access to other content such as journal papers, practical management guides and reports. CABI also offers the Horizon Scanning Tool, which identifies potentially invasive species at risk of entering a particular geographic area, and the Pest Risk Analysis Tool, which uses extensive plant pest data from the Crop Protection Compendium to provide a framework for assessing and managing pest risks. Both of these tools are designed to support decision-making in biosecurity and proactive management of invasive species.

Further reading

Reference: Jean E. Fantle-Lepczyk, Phillip J. Haubrock, Andrew M. Kramer, Ross N. Cuthbert, Anna J. Turbelin, Robert Crystal-Ornelas, Christophe Diagne, Franck Courchamp. Economic costs of biological invasions in the United States. BioRxiv 2021.07.02.450757; DOI: https://doi.org/10.1101/2021.07.02.450757

The above article is a preprint and has not been formally peer reviewed. It may be subject to significant revisions prior to journal publication, and results should not be interpreted as conclusive.

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