It is one of the most characteristic semi-aquatic mammals of South American wetlands and a frequent inhabitant of lagoons, marshes, swamps, slow-moving rivers, and other freshwater environments. Myocastor coypus is a medium- to large-sized rodent with a robust, elongated body specially adapted for movement both on land and in water. Its fur is dense and composed of long, coarse guard hairs that protect a thick, soft, waterproof underfur, an essential adaptation for maintaining body temperature in aquatic habitats. Overall coloration ranges from dark brown and reddish-brown to grayish-brown, with the underparts generally somewhat paler. The head is relatively large, with small eyes, short ears, and a muzzle equipped with numerous sensitive whiskers. One of its most distinctive features is the presence of large bright orange incisors, whose coloration results from iron-rich enamel. The hind feet are long and equipped with well-developed webbing between the toes, providing excellent swimming ability. The tail is cylindrical, relatively long, and sparsely covered with hair. Males and females are similar in appearance, although males generally reach slightly larger sizes. A remarkable adaptation of females is the elevated position of the mammary glands along the flanks, allowing young to nurse while the mother remains partially submerged.
Geographic distribution: The species is native to central and southern South America. Its natural range includes most of Argentina, Uruguay, Chile, Paraguay, southern Brazil, and parts of Bolivia. Within this broad distribution it occupies numerous wetland systems, ranging from temperate environments to subtropical regions. Due to the historical commercial value of its fur, it was introduced into several parts of North America, Europe, Asia, and Africa, where wild populations became established in many areas. In some of these regions it has become an invasive species with significant ecological impacts on wetland ecosystems. Throughout its native range, however, it remains a common and important component of aquatic habitats.
Habitat: It primarily inhabits lagoons, marshes, swamps, wetlands, streams, canals, reservoirs, and slow-flowing rivers, particularly those with abundant emergent and shoreline vegetation. It shows a preference for habitats dominated by reeds, cattails, rushes, and other dense aquatic plant communities that provide food, shelter, and breeding sites. The species can also adapt to artificial water bodies created by human activities, provided that suitable vegetation is present. Permanent access to water is one of the most important factors determining its distribution and survival.
Diet: It is a predominantly herbivorous mammal, specialized in feeding on aquatic and riparian vegetation. Its diet includes leaves, stems, roots, shoots, rhizomes, and other tender plant parts from a wide variety of species. Reeds, cattails, grasses, and numerous emergent wetland plants are frequently consumed. In some areas it may also feed on agricultural crops located near water bodies. Although occasional consumption of small invertebrates has been recorded, animal matter represents only a negligible portion of its diet. Feeding activity usually peaks during twilight and nighttime hours, although individuals may remain active throughout the day in undisturbed habitats.
Behavior: It displays mainly semi-aquatic, crepuscular, and social habits. It is an excellent swimmer and diver, capable of remaining underwater for several minutes when threatened. Individuals commonly live in family groups composed of a breeding pair and offspring of different ages. Well-defined trails are often created between feeding areas and water bodies, producing visible pathways through the vegetation. The species may construct feeding and resting platforms from aquatic plants and also uses burrows excavated into banks and shorelines. Communication involves vocalizations, scent marking, and body postures that help maintain social cohesion and warn of potential danger.
Reproduction: The species has a high reproductive capacity and may breed throughout much of the year, especially in regions with favorable environmental conditions. Gestation lasts approximately 125 to 140 days, one of the longest periods among rodents. Litters usually contain four to six young, although larger or smaller numbers may occur depending on local conditions. Newborns are highly developed, emerging with fur, open eyes, and the ability to move and swim shortly after birth. Females provide intensive care during the first weeks of life, while juveniles gradually learn to forage independently and navigate aquatic environments. Under favorable conditions, more than one litter may be produced annually.
Conservation status: Globally, the species is classified as Least Concern (LC) due to its broad distribution, adaptability, and abundance throughout much of its native range. Nevertheless, some local populations may be affected by wetland degradation, water pollution, hydrological alterations, and hunting pressure. The conservation of marshes, swamps, lagoons, and other wetlands is essential for ensuring the long-term persistence of this species and the many biological communities associated with these ecosystems. Interestingly, while it is a natural component of biodiversity within its native range, it is regarded as an invasive species requiring management and control measures in several countries where it has been introduced.
Author of this compilation: EcoRegistros – 21/06/2026