Coypú or swamp beaver?  Actually, both are common names of the aquatic mammal we most frequently call the Nutria (Myocastor coypus).  Or, is it nutra, neutral, or neutral rat, as frequently mispronounced in south Louisiana?

Now one of our most familiar rodents, the nutria had a most interesting introduction to our continent from its native Argentina.  A few were released in the marshes around New Orleans during the early 1930’s, but were presumably all captured by trappers.  About that time, the great Louisiana naturalist, E. A. McIlhenny, better known for his famous Tabasco hot sauce, imported 20 or so nutria (at the suggestion of the Louisiana Department of Wildlife & Fisheries) and placed them in an enclosure at his wildlife refuge on Avery Island near New Iberia.  The nutria did well, and in the late 1930’s they were released into the surrounding marshes (though it has always been believed that a storm allowed their escape!).

The stage was set - miles and miles of suitable habitat virtually devoid of competitors.  An additional positive feature was that there were only two real potential predators for adult nutria:  large alligators and humans.  Juveniles, however, are preyed upon by an assortment of predators such as snakes, turtles, gar, and some raptors.

At first, the trapper considered them a nuisance, but once the value of the pelt and carcass were realized, the nutria became economically valuable.  In less than 30 years, nutria became the number one fur crop in the U.S., with most pelts going to France where they were popular wear.  For some reason, they never caught on in the U.S., even though they were marketed as Hudson Bay Seal, a name that drew attention to their pelt’s similarity to seal fur while hiding its less than attractive source!  They continue today to be utilitarian wear in southern South America.

There is a connection between nutria and a beautiful yellow flower that literally covers the surface of swamps and freshwater marshes each fall.  This flower is Sticktight, or Smooth Beggertick (Bidens laevis or B. cernua, flowers erect in the former and nodding in the latter), but better known as fourchette in south Louisiana.  These flowers produce a seed that has barbed awns which hook into the skin of nutria, causing a severe dermatitis and ruining the pelt.  It is strange that a plant that provides such beauty can have such a devastating affect on the economy!

Nutria are strict vegetarians, but they do not eat only nuisance plants such as water hyacinth and alligatorweed.  They eat a wide variety of species, including rice and sugarcane.  Their messy feeding habits make them particularly wasteful - they only consume 10% of what they cut down with their sharp incisors. 

Nutria are aquatic by nature and live in burrows.  This habit frequently causes problems for humans, because their burrows weaken levees.  In areas with tall vegetation, they often form “hides” by tunneling about under matted grass.

They are quite social and family units may stay together for a time.  Their babies frequently cling to their backs as the adults swim about.  Nutria can often be heard calling to one another in the wetlands.  Their voices sound like “m-e-e-w” or a nasal “nan-cy.”

Humans who work in the marsh may get an occasionally case of nutria itch, resulting in severe itching and swelling.  It is caused by a small roundworm (a nematode of the genus Strongyloides, strong eh loy’ dees) that is parasitic in nutria intestines.  Nematode eggs leave the nutria in its feces, and they hatch into tiny larvae that swim about in the water.  Normally, these larvae burrow into a nutria, become adults, and the cycle begins again.  If some hapless human who is not wearing boots comes along, the larvae burrow into his or her skin.  Since humans are not the normal host, the larvae burrow about until they die.  The whole process can cause three weeks of unmitigated agony!

              Since they are now rarely hunted and the number of large alligators has declined, nutria populations in Louisiana have experienced uncontrolled expansion.  Due to predation, disease, and other factors, the average nutria probably lives three or four years in the wild.  They begin breeding on average at about 6 months of age.  Gestation is approximately 130 days, litters are usually four or five, and mating typically occurs about 48 hours after birth.  Putting the pencil to paper with these facts tells us that by the end of its first year, a female nutria can have produced one litter and be two months into a second litter.  Coincidental with her first birthday is that her first babies are now sexually mature and breeding and, like their mom, will produce 12-15 babies per year for 3-4 years!  Studies by Louisiana Department of Wildlife & Fisheries have shown that brackish marsh can sustain a maximum of nine nutria per acre, and freshwater marsh can sustain 18 per acre.  At 640 acres per square mile, some sites in Louisiana could be populated by as many as 11,520 nutria per square mile; 6,000 have been documented by scientists!!!  When the populations of these ravenous critters get too high, they may eat all the vegetation, including the roots.  This results in barren areas, sometimes hundreds of acres in size, referred to as “eat outs.”  This leaves the marsh vulnerable to further destruction by natural forces.  Marsh ecologists now believe that the uncontrolled nutria population is a major contributor to the demise of our coastal wetlands. 

So, nutria are eating out coastal marshes since there is no present market for their pelts?  What are we to do?  Let’s eat them!  They actually have a wonderfully lean meat that tastes great.  Just after World War II, they were sold in the U.S. as Hoover Hogs.  Nutria is marketed in Europe under the name ragondin (the French name for nutria).  Obviously, we have to convince folks that they are not rats (note:  not all “rodents” are “rats”, e.g., squirrels).  We may get a little help from science.



Or, We Can Eat Nutria Because They May Not Be Rats

The mammalian Order Rodentia (commonly called the rats) have traditionally been divided into three suborders:

Suborder Myomorpha - rats, mice, voles, lemmings, gerbils, hamsters, jerboas, etc.
Suborder Sciuromorpha - squirrel-like rodents:  squirrels, marmots, kangaroo rats, beavers, etc.

Suborder Hystricomorpha -

Old World - mole rats, cane rats, dassie rats, Old World porcupines, etc.
New World - guinea pigs, nutria, chinchillas, agoutis, pacas, capybaras, New World porcupines, etc.

Similarities that have bound these three groups have been morphological in nature:

-gnawing mammals

-adaptations of the incisors, molars, and musculoskeletal features of the masticatory (chewing) apparatus enhancing gnawing

-certain shared features of the post-cranial skeleton, placental and fetal membranes, carotid arterial patterns, and myology (muscles).

Suggestions that any or all of these three suborders are unrelated must overcome a long traditional definition of the Rodentia.  Though this has not happened, it has been suggested that the members of the New World hystricomorphs, called the Caviomorpha, are an identifiable unit, separate from the myomorphs, sciuromorphs, and Old World hystricomorphs, on the basis of amino-acid sequence(DNA) analysis.  These data indicate that the caviomorphs (represented by the guinea pig in the studies) diverged from the myomorphs before the primates (humans, monkeys, apes, etc.) and artiodactyls (cows, pigs, deer, and relatives).  If this is true, then it indicates that caviomorphs are not closely related genetically to the myomorphs and should be recognized as a different order.  This would mean that the morphological similarities are due to convergent evolution, i.e., they lead similar lifestyles so Mother Nature has selected a similar set of external features for them to share.

The jury will be out on this topic as more scientific information is accumulated, but it appears that there has been a rather ancient divergence genetically between caviomorphs and the rest of the Rodentia.