The nutria, also known as the coypu, is a large, semi-aquatic rodent native to South America. Known for its powerful burrowing and voracious appetite for wetland vegetation, it has become established in numerous regions worldwide. Outside of its natural range, the nutria is classified as an invasive species due to the severe environmental and infrastructural damage it causes. Its ability to reproduce rapidly and lack of natural predators allow populations to grow unchecked, leading to significant ecosystem disruption.
Identification and Native Habitat
The nutria (Myocastor coypus) possesses several features that distinguish it from similar native rodents like the beaver or muskrat. Adults can weigh up to 20 pounds and measure about two feet in length. A key identifier is its long, thin, and rounded tail, which differs significantly from the beaver’s flat tail or the muskrat’s laterally compressed tail. The animal also has prominent, bright orange incisor teeth, visible even when its mouth is closed.
Highly adapted for a semi-aquatic lifestyle, the nutria has small eyes, ears, and nostrils positioned high on its head, allowing it to remain submerged. Its hind feet are partially webbed, aiding in efficient swimming. The native range of the nutria is the southern half of South America, including Argentina, Chile, Uruguay, Paraguay, southern Brazil, and Bolivia.
Global Spread and Current Range
The nutria’s expansion began with the international fur trade in the late 19th and early 20th centuries. Fur farmers sought the nutria’s soft, dense underfur, leading to its intentional introduction to North America and Europe. The earliest U.S. introductions occurred in California in 1899, followed by others in the 1930s, particularly in Louisiana.
Feral populations were established through accidental escapes and deliberate releases from these farms. When the demand for nutria fur declined in the mid-1900s, many farmers released their stock into the wild rather than continue feeding them. Today, the nutria is established across at least 20 U.S. states, notably along the Gulf Coast and in the Pacific Northwest, and is also found across Europe and parts of Asia.
Ecological and Infrastructure Impact
The most significant problem posed by invasive nutria populations stems from their destructive feeding behavior, often called “nutria eat-outs.” These rodents are voracious herbivores, capable of consuming approximately 25% of their body weight in vegetation daily. Nutria consume the entire plant, including the roots, rhizomes, and tubers necessary for stabilizing wetland soil. This intensive root-grazing rapidly destroys vegetation, leading to severe erosion and the conversion of productive marshland into open water. Such habitat loss threatens native plant and animal species that rely on the wetlands for survival.
Beyond natural habitats, nutria cause extensive damage to agricultural operations, feeding on high-value crops such as rice, corn, and sugarcane. Nutria also pose a direct threat to human infrastructure through their prolific burrowing habits. They excavate extensive tunnel systems that can reach up to 150 feet in length along the banks of waterways. This burrowing weakens the structural integrity of flood-control levees, irrigation canals, roadbeds, and dikes, potentially leading to costly failures and flooding risks. Furthermore, nutria carry various pathogens and parasites that can be transmitted to humans and livestock, making them a public health concern.
Management and Control Efforts
Controlling invasive nutria populations requires a sustained, multi-faceted approach. One common strategy involves various trapping methods, utilizing live traps, kill traps, and body-gripping traps like the Conibear® set in trails or at den entrances. In regions like coastal Louisiana, state-funded programs incentivize trappers and hunters by offering a bounty payment per tail to increase the annual harvest.
Exclusion methods are also employed, such as using low fences with a buried apron to deter nutria from gardens, or installing bulkheads to prevent burrowing into embankments. Habitat manipulation, such as deep plowing to destroy dens or managing water levels to stress the animals, also contributes to localized control. Management challenges are compounded by their high reproductive output and ability to quickly re-colonize controlled areas, necessitating continuous monitoring and removal efforts.