Twin Sons of Different Mothers

Corvallis Oregon, home of Oregon State University and capital of Beaver Nation, very likely has the highest concentration of beaver fans in the world. Beavers are likeable animals. Large for a rodent but industrious (busy as a… ), these clever engineers build dams and design homes with underwater entries. So why is it their distant relatives, the nutria, are reviled by those who know them?

If you think I overstate the animosity, consider this: I had a coworker, Marilyn, well-known as a master gardner, who woke up one morning and spotted a nutria munching in her lettuce patch. Marilyn grabbed her husband’s .22 rimfire rifle from the closet and loaded it. She propped it on the sill of her second floor bedroom window, carefully sighted down the barrel and shot the nutria between the eyes. Marilyn later informed me this was the first time she had ever shot a gun. I have other examples, but they are pretty violent, so I will move on.

The nutria (Myocastor coypus) is a large semi-aquatic mammal often confused with beavers or muskrats. Adult nutria weigh ten to twenty pounds and measure one to two feet in length without the tail, placing them between beaver and muskrat in size . Probably the most distinguishing (and least endearing) physical feature of the nutria is their thin, round, sparsely-haired, scaly tail. [1] On land, nutria appear hunched due to disproportionately long hind legs. Picture a 20-pound rat named Igor.


O.K. So this is not the most handsome mammal on the planet. What else?

A visit to the Oregon Department of Fish and Wildlife website [3] starts you out with a description of the damage and destruction wreaked by nutria burrowing, then continues with the rodent’s “depredation” on crops and natural plant communities. The site notes aggressive competition with the smaller muskrat. This naturally segues into nutria’s status as unprotected wildlife which can be trapped (but not relocated) and shot.

Still. Beavers girdle trees, their dams can cause flooding; but for their flat tails, they would also look like ROUS (rodents of unusual size). Here is the rub: nutria are native to South America. They were introduced around the turn of the century by the fur industry. They are not one of ours.

So nutria are non-native. So what? There are many non-native species we would happily call our own: cats, horses, European honeybees, and Norway maples to name a few. The trouble starts when a species crosses the line and becomes “invasive.” That is when the government gets involved. From [4]: “Executive order 13112 defines an invasive species as an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” Igor is on the federal Most Unwanted list.

Nutria have a well-documented history of wreaking economic and environmental havoc in Maryland, Louisiana and Texas, where there are multi-million dollar programs to manage them. In a recent presentation at the Tualatin National Wildlife Refuge [5], Dr. Trevor Sheffels, one of the forefront researchers of nutria management in the Pacific Northwest, stated that the public needs to know nutria are non-native, and invasive. They are prodigious breeders, reproducing up to 3 times a year, with an average litter size of 4 to 5 and a maximum of 13. Nutria prefer the basal succulent portions of plants, wasting up to 90% of the plant while eating 25% of their weight, daily. Doing the math, a large, wasteful nutria could consume up to 5 pounds of vegetation and waste 45 pounds. Daily. That’s bad, but probably not of immediate concern to the homeowners in Sheffels’ presentation whose house tilts into a creek, the creekbed destablized by nutria burrows.

Start the scary music. “In the year 2050 we show that almost all of the states are suitable for nutria [due to climate change],” said Catherine Jarnevich, a research ecologist with the USGS. The research, not yet published, was presented at the recent meeting of the Ecological Society of America in Minneapolis [6].  Sheffels states that with the current regional population size and prolific reproduction, a long term, high cost program would be needed to attempt eradication in the Pacific Northwest [7]. No wonder folks don’t like them.

[1] Maser, C., et. al. 1981. Natural History of Oregon Coast Mammals. USDA Forest Service Gen. Tech. Rep. PNW-133, p. 146.
[2] Visited 11/20/2013.
[3] Visited 11/19/2013.
[4] Visited 11/19/2013.
[5] Sheffels, Trevor. Extended Learning Program – Nutria, Tualatin National Wildlife Refuge, November 5, 2013
[6] Visited 12/15/2013
[7] Sheffels, Trevor and Mark Systma. “Report on Nutria Management and Research in the Pacific Northwest” Center for Lakes and Reservoir Environmental Sciences and Resources, Portland State University. December 2007. Available on-line: Visited 11/18/2013.