Myocastor coypus - Nutria

Physical Description:

Myocastor coypus is described as being a “giant muskrat” and this proves to be very true.  Like muskrats, they have a long scale-like tail that is slightly hairy that ranges from 340 mm to 405 mm on average in length and a robust rat-like body, which ranges from 472 mm to 575 mm in length.  Its’ weight ranges anywhere from 11 lbs to 22 lbs and males usually tend to be larger than females.  It has four enlarged front teeth that are orange pigmented and its’ head is triangular shaped with small eyes and small ears.  It has short legs; the hind feet are longer than the front feet and contain 4 digits that are webbed with a fifth digit, which is considered the thumb and meant for grooming.  Unlike most mammals, the female has four teats that are found further up on the side of the body; in fact, the teats are so high up they are almost located side of the myocastor coypus.  Like all furbearers, it has short, dense underfur and long coarse guard hairs that can range in color from a light brown (almost yellow) to a dark black to a bright reddish brown (Woods 1992).

Geographical region:

Myocastor coypus is native in southern and central part of South America.  The distribution extends from central Bolivia down to the southern tip of Argentina.  Myocastor coypus has also invaded Europe, North America, and Asia due to being raised in fur farms and released or escaped from these farms (Redford 1992). 

Ontogeny and Reproduction:

Myocastor coypus has a high reproduction rate.  A female can reach sexual maturity at six months of age and can bear anywhere from 3 to 6 young pending the season.  It is a non-seasonal breeder meaning that it breeds whenever it is ready to bear a litter.  A female can have up to three litters in a year pending the circumstances.  Limiting factors that control female breeding capability are food availability, weather, predators, and disease.  The length of gestation can range anywhere from 127 to 139 days.  Once the young are born, they are precocial and grow at an accelerated rate being only cared for by the mother.  The young are weaned in less than two months.  The average lifespan of the myocastor coypus is 6.3 years give or take .4 of a year (Woods 1992).

Myocastor coypus mortality consist of primarily of predators, disease, and human-control methods.  The biggest mortality factor is human control methods, which can consist of shooting, trapping, and poisoning.  The myocastor coypus has very few predators, but what predators it does have consist of pumas, red wolves, hawks, and anacondas (Woods 1992).

Ecology and Behavior:

Myocastor coypus is a semi aquatic mammal that is nocturnal and is very socialable.  These social groups consist anywhere from 2 to 13 in a group and a group usually consists of related adult females, their litters, and one adult male.  At times, young males take up a solitary life due to being forced from a social group (Guichon 2003).  Myocastor coypus spend most of its time feeding, grooming, and swimming.  Its grooming claw is located on the separated digit on the hind foot and it releases oil, which it spreads over its body with its fore paws.   It does this to keep its body “water proof”.  Myocastor coypus live in bank dens, which it digs itself and can range from anywhere from 3 to 18 feet long and can contain up to seven entrances (Woods 1992).

Myocastor coypus are herbivores.  Their diet consists primarily of aquatic vegetation, however, they have been known to invade cropland areas and do extensive damage to growing crops (Malekian 2000).

Myocastor coypus serves as an economic importance to humans.  They are continually killed for food and fur purposes.  In South America, they very seldom become a nuisance unless population density is high, however, in North America, particularly the Gulf coast, Myocastor coypus has became an extreme nuisance destroying vast amounts of shoreline with its’ burrows and frequently destroying cropland and tree growth.  Nuisance control methods have been taken, which are slowing down the population boom, however, their population is still increasing (Woods 1992).

Myocastor coypus live in a variety of aquatic habitat.  The quality of the aquatic environment that it lives in includes waterways, rivers, lakes, and marshes.  The areas that myocastor coypus thrive well in are areas that contain succulent vegetation along the shores and banks of any aquatic habitat.  Though it prefers to live in fresh water, current populations have been able to live in salt-water habitats (Nowak 1999).

Literature Cited:

Guichon.  2003. Population Structure of Coypus in their Region of Origin and Comparison with Introduced Populations.  Journal of Zoology 261:265

Malekian.  2000.  Analysis of the nutritional content of Myocastor coypus.  Journal of Food Composition and Analysis.  13:117

Woods.  1992.  Myocastor coypus.  Mammalian Species 398:1-8

Redford, K.H. and J.F. Eisenberg. 1992 Mammals of the Neotropics.   Vol. 2. University of Chicago Press. 353-354

Nowak, R.M. 1999. Walker’s Mammals of the World.  6th edition. Vol. 2. The John Hopkins University Press. 1712-1714

Reference written by Aaron Geistfeld, Biology 378 student.  Edited by Christopher Yahnke. Page last updated August 8, 2005.