In the spring of 1943, five nutria escaped a research enclosure at a federal fur-animal station on Blackwater’s marsh in Dorchester County, Maryland, and were later found dead in a nearby boathouse. That small, mostly overlooked event, recorded by Smithsonian’s Chesapeake Bay invasive-species database, marks the start of one of the longest wildlife-removal campaigns ever completed in the United States. It would take nearly eight decades, a coordinated federal-state program running more than 20 years, over 14,000 animals removed, cooperation from more than 700 private landowners, and a fleet of specially trained dogs before officials could say the marshes of the Delmarva Peninsula were clear.

How a Fur Experiment Became an Invasion

Nutria, or Myocastor coypus, are large semi-aquatic rodents native to South America, prized in the early twentieth century for their soft underfur. The federal government brought the first animals to a fur research station at what is now Blackwater National Wildlife Refuge in 1939, hoping to establish an alternative to the region’s declining muskrat trade. According to the Smithsonian Environmental Research Center’s Chesapeake Bay invasion database, the 1943 boathouse escape was followed by additional releases, some accidental and some deliberate, as local trappers and landowners tried their hand at raising the animals for fur.

Nutria breed quickly and eat voraciously, and they lack natural predators on the Eastern Shore. Unlike muskrats, which crop marsh vegetation without killing the root mat, nutria dig up roots and rhizomes, converting healthy marsh into open mudflat and shallow water. Maryland’s Department of Natural Resources describes the resulting damage as the destruction of thousands of acres of wetland habitat, and refuge managers at Blackwater have said the refuge itself lost more than 5,000 acres of marsh to a combination of nutria feeding, sea-level rise, and land subsidence over the following decades. By the 1990s, biologists estimated the regional population at roughly 100,000 animals spread across Delmarva’s tidal marshes.

Building a Program to Remove Every Last One

Early, informal attempts to control nutria date back to at least the 1950s, but they did little to slow the spread. The turning point came in the late 1990s, when the U.S. Fish and Wildlife Service and Maryland DNR, working with roughly a dozen partner agencies, concluded that eradication, not just population control, was technically feasible if the marshes were surveyed thoroughly enough. A pilot project tested trapping and marsh-recovery methods, and in April 2002 the Chesapeake Bay Nutria Eradication Project began in earnest, led by the Fish and Wildlife Service with USDA’s Animal and Plant Health Inspection Service, Wildlife Services, handling most of the fieldwork alongside Maryland DNR and university researchers.

The project depended on access to private land, since nutria did not respect refuge boundaries. Field crews eventually worked with more than 700 landowners across the Delmarva Peninsula, trapping and removing animals from public refuges, farms, and private wetlands alike. Over the life of the program, crews removed more than 14,000 nutria, with roughly half taken from private property. Researchers also used radio-collared, sterilized “Judas” nutria, released to seek out surviving groups of their own kind, a technique first added around 2009 that helped crews find animals in dense marsh where trapping alone was inefficient.

The Hardest Part Was Proving a Negative

Removing the bulk of a large, fast-breeding population turned out to be easier than confirming that none remained. By the early 2010s, trapping success had dropped so low that crews needed a more sensitive way to detect the last few animals scattered across a landscape of more than 250,000 acres. Starting in 2014, the project brought in specially trained detector dogs, working with handlers to search for nutria scat rather than the animals themselves, since scat is far more detectable across dense marsh vegetation than a wary, largely nocturnal rodent. The U.S. Geological Survey published a related evaluation of the project’s ground-based detection methods, finding that hair snares performed about as well as trail cameras and clearly outperformed scat surveys alone; detector dogs were added to the project’s toolkit around the same period but were not part of this particular USGS comparison.

That verification effort paid off. The last nutria confirmed in the wild on the Delmarva Peninsula was captured in May 2015. But program leaders did not declare victory then. Eradication claims require proving absence, a higher bar than simply not catching anything new, so field teams spent several more years conducting systematic surveys across the entire treated range before agencies were confident no breeding population remained. The Fish and Wildlife Service, together with USDA and Maryland DNR, formally declared the Delmarva Peninsula free of invasive nutria in September 2022, at an event held at Blackwater National Wildlife Refuge, seven years after that last capture and roughly two decades after the coordinated eradication project began.

What the Record Actually Shows

Several details commonly repeated about this history need adjusting against primary sources. The escape itself is well documented: five nutria did get out of a research facility on Blackwater’s marsh and were found in a boathouse in the spring of 1943, according to Smithsonian’s Chesapeake Bay invasive-species reporting. The 14,000-animal removal total and the more-than-700 landowner figure both match the Fish and Wildlife Service’s own account of the completed project. The “20 years” claim is accurate only if it refers to the formal removal campaign, which ran from April 2002 to the September 2022 declaration, not to the interval between the 1943 escape and the program’s end, which spanned closer to 80 years. And while a detector dog team did find the last confirmed nutria in May 2015, that discovery did not end the project. It began a lengthy, methodical verification phase, because officials needed years of clean surveys before they could rule out a hidden remnant population, a step nutria eradication programs in other parts of the world have skipped at their peril.

Nutria have not been eliminated from the United States generally. Louisiana, Texas, and other Gulf Coast states still manage large, permanent populations, and isolated nutria have turned up elsewhere on the East Coast since the Maryland program concluded, prompting monitoring efforts in neighboring states. What the Chesapeake Bay project demonstrated was narrower and still significant: that a localized, self-sustaining population of an invasive semi-aquatic rodent could be fully removed from a large wetland landscape, given enough time, enough landowner cooperation, and, in the end, dogs trained to smell what traps could no longer catch.