Emerald ash borer in North America (2002–present)
An Asian beetle found in Michigan in 2002 spread across North America and killed hundreds of millions of ash trees. Despite quarantine efforts, it reached 35 states plus Canadian provinces within two decades.
Millions of dead ash trees fell across cities and forests, creating safety hazards and cleanup costs in the billions.
The case showed that a single invasive pest moving through trade routes can reshape a continent's tree cover.
A parallel example of how an imported pest, once established, can overwhelm even coordinated quarantine campaigns.
