Rattus deathicus: America's War on Invasive Nutria

Image used with permissions under creative commons.

Throughout my career in the wildlife control industry, there’s few mammals I’ve become more familiar with than rodents. Rats, mice, beaver, squirrels, voles, muskrats - the list goes on, and there’s no doubt rodents have proven themselves prolific and resilient for millennia; especially in the face of man’s own hostile takeover. While mice and rats are more commonly handled by the commercial pest control industry, there’s one particular rodent that has kept some wildlife agencies and professional trappers busy for several decades.

Enter Myocastor coypus - the Nutria.

The nutria, often referred to as coypu, is a medium sized sub-aquatic rodent indigenous to South America. Similar to muskrats, nutria will feed on roots and tubers of many marsh plants, and can cause immense erosion and damage in the process. Similar to beaver, the nutria comes equipped with quite a set of headgear, in the form of enlarged front teeth for gnawing. Since their introduction, as early as 1899 in California, nutria have expanded to over 15 states - in varying degrees from isolated “feral” populations to full blown (and noticeable) presence. I haven’t had the pleasure of bearing witness to one here in the Granite State. Although northern US climates tend to be less desirable, reports of nutria activity stretch as far north as Massachusetts (Plum Island, in 2002). In the states they do reside, they continue to promote a varying range of concerns and issues for state agencies tasked with environmental and wildlife regulation.

Unlike the muskrat and beaver however, the nutria doesn’t technically belong here in the United States. So where did it come from? And why aren’t we simply “co-existing” with this furry little invader?

Public Domain Image

How’d They Get Here?

Throughout the 1930’s and 40’s, nutria were shipped into several states to reside on private farms for their fur. Farms and ranches in the business of raising nutria for their hides was common during the 20th century fur-boom. This is important to note, as some have incorrectly cited early fur trappers as the cause of nutria introduction. The reality is that fur farms (which at the time were under-regulated) were the catalyst for the initial introduction of nutria to the United States. It wasn’t long before nutria in several states escaped the poorly constructed pens, or were released into the wild when fur farms shut down due to lack of interest. Early trappers would actually play a part in the nutria’s control and removal when “escapees” from those fur ranches would find their way into the local marshes of states like Louisiana. While it has been rumored some fur farmers allegedly discussed a desire to intentionally create a nutria-trapping industry - all accounts I can find seem to cite these theories as merely lore and legend. Businessmen with crappy fencing - that seems to be our smoking gun!

During the 1940’s and 50’s, the spread of nutria was exacerbated when many states purposely introduced nutria as weed control agents. It seems as though the nutria were a little “too good” at their plant removal, and between prolific breeding and an appetite for all kinds of aquatic vegetation, these water-logged “brush-hogs” began to have a detrimental effect on their newly introduced landscape.

The United States Geological Survey has a nifty little timeline of nutria introduction that sums up these events nicely, along with a state-by-state breakdown.

Trapping, Management, and Eradication

Some states have accepted the fact that they have small pockets of “feral” nutria populations, and have created regulated trapping seasons to manage those populations. Other states, however, have launched all out war on the little buggers. Maryland, for example, has been very successful with their nutria eradication program. So what happens when managers opt to eradicate, rather than cohabitate?

Regulated trapping in a seasonal fashion is established for long-term conservation of a given furbearing species - it doesn’t cause wildlife to become endangered. It seeks to balance wildlife populations and conserve resources while also removing surplus or nuisance individuals.

Eradication however, such as the case with nutria in the Chesapeake Bay area, utilizes professional trapping techniques with the goal of completely removing a problem or invasive species.

Effective nutria trapping includes 220 or 160 lethal traps set precisely in aquatic runs and grassy marsh trails. Modern foothold traps affixed to submersion wires set at the base of baited scent mounds have also proven effective. Identifying feeding beds, rich with food debris and scat, and worn down trails and travel-ways are key to success. Lures include Pennyroyal and Rhodium oils, baited with carrots, apples and cabbage. On occasion, sharpshooters with rifles have been utilized to eliminate individual nutria when spotted, and many infected states offer a nutria hunting season or bounty system for skilled marksmen.

A very compelling image showing nutria damage (left) prior to removal. Followed by the after effects of the land regeneration after nutria removal (right).

There’s been very little public opposition to nutria eradication, because I think the ecological justification for what we’re doing is so compelling. You really can’t argue that they don’t belong here.
— Stephen Kendrot, USDA Nutria Eradication Project Leader

Without the pressures of a fur trade as popular as it once was, and a nonnative rodent expanding its population, many state agencies are heavily weighing their options. Whether its erosion from their dens and burrows, or trampled feed beds wiping out viable marsh vegetation, conservation-minded groups and citizens are typically willing to step aside and let licensed trappers answer the call.

According to the US Fish & Wildlife Service, a 2004 economic study commissioned by the Maryland DNR reported upwards of 35,000 acres of Chesapeake Bay marshlands could potentially be destroyed by nutria within 50 years. USDA’s APHIS Wildlife Services division has undertaken the brunt of the eradication challenge, and, with the assistance of USFWS and Maryland DNR, it proved very successful. All-out annihilation of the subaquatic rats was targeted, and in many regions, carried out. Managers even went as far as to fit nutria with tracking devices, which would lead hunters and trappers to small caches of nutria “hold-outs” in a battle dubbed The Judas Project - clearly, all’s fair in love and war.

Invasive Pest or Furbearing Resource?

Samples and data are taken from a caged nutria. (Public Domain Image)

While states like Maryland and Delaware are actively looking to abolish their nutria populations, states in the deep south seem to be slightly less agressive. The coypu is highly regarded in regions around the Gulf of Mexico and southern U.S. Delta waterways; ironically, some of the first areas where nutria were introduced. Both Louisiana and Texas actually have regulated hunting and trapping seasons on the rodents. Cajun trappers of the Barataria region regard the nutria as an important staple of tradition and as an important community resource. Food and fur - and while the nutria pelt has its own commercial value, I’m told nutria meat is actually pretty tasty as well; no surprise, as trappers like myself are well accustomed to the table-fare of baked muskrat and beaver stew!

That said, even states with harvest seasons and bag limits recognize the absolute chaos nutria can inflict upon marshlands when not properly managed. The Louisiana Coastwide Nutria Control Program is quoted as stating “The decline in fur trapping activity since the mid-1980s has resulted in over population of nutria.” My personal translation - there aren’t as many trappers as there once was, and without regulated trapping activities taking place on the landscape, “big guns” are called in to heavily cull instead. Unlike civilian trappers, I’m willing to gamble each individual animal’s resources (pelt, hide, meat etc.) aren’t being fully utilized when the need arises for an eradication situation.

As invasive and out-of-place as the nutria may seem, it also plays a crucial role in defending the activity of modern trapping today, and a need for trapper support going forward. The nutria not only demonstrates a critical need for skilled trappers on the landscape, but its my personal opinion that these adaptive marsh rats also clearly show the ramifications when a species is not managed properly, and comes to be regarded as a pest rather than a cherished resource.


References from the USFWS, USDA APHIS, US Dept. of the Interior, University of Nebraska - Lincoln, and the U.S. Geological Survey assisted with this column.