Prevention and Control Methods Exclusion
Protect small areas with partially buried fences.
Wire tubes can be used to protect baldcypress or
other seedlings but are expensive and difficult to
Use sheet metal shields to prevent gnawing on wooden
and styrofoam structures and trees near aquatic
Install bulkheads to deter burrowing into banks.
- Cultural Methods
and Habitat Modification
Improve drainage to destroy travel lanes.
Manage vegetation to eliminate food and cover.
Contour stream banks to control burrowing.
Plant baldcypress seedlings in the fall to minimize
Restrict farming, building construction, and other
“high risk” activities to upland sites away from
water to prevent damage.
Manipulate water levels to stress nutria
None are registered. None are effective.
Zinc phosphide on carrot or sweet potato baits.
None are registered. None are effective.
Commercial harvest by trappers.
Double longspring traps, Nos. 11 and 2, as preferred
by trappers and wildlife damage control specialists.
Body-gripping traps, for example, Conibear® Nos.
160-2 and 220-2, and locking snares are most
effective when set in trails, den entrances, or
Live traps should be used when leghold and
body-gripping traps cannot be set.
Long-handled dip nets can be used to catch unwary
Effective when environmental conditions force nutria
into the open. Night hunting is illegal in many
- Other Methods
Available control techniques may not be applicable
to all damage situations. In these cases, safe and
effective methods must be tailored to specific
The nutria (Myocastor
coypus, Fig. 1) is a large, dark-colored,
semiaquatic rodent that is native to southern South
America. At first glance, a casual observer may
misidentify a nutria as either a beaver (Castor
canadensis) or a muskrat (Ondatra zibethicus),
especially when it is swimming. This superficial
resemblance ends when a more detailed study of the
animal is made. Other names used for the nutria include
coypu, nutria-rat, South American beaver, Argentine
beaver, and swamp beaver.
Nutria are members of the
family Myocastoridae. They have short legs and a robust,
highly arched body that is approximately 24 inches (61
cm) long. Their round tail is from 13 to 16 inches (33
to 41 cm) long and scantily haired. Males are slightly
larger than females;the average weight for each is about
(5.4 kg). Males and
females may grow to 20 pounds (9.1 kg) and 18 pounds
(8.2 kg), respectively.
The dense grayish underfur
is overlaid by long, glossy guard hairs that vary in
color from dark brown to yellowish brown. The forepaws
have four well-developed and clawed toes and one
vestigial toe. Four of the five clawed toes on the hind
foot are interconnected by webbing; the fifth outer toe
is free. The hind legs are much larger than the
forelegs. When moving on land, a nutria may drag its
chest and appear to hunch its back. Like beavers, nutria
have large incisors that are yel-low-orange to
orange-red on their outer surfaces.
In addition to having
webbed hind feet, nutria have several other adaptations
to a semiaquatic life. The eyes, ears, and nostrils of
nutria are set high on their heads. Additionally, the
nostrils and mouth have valves that seal out water while
swimming, diving, or feeding underwater. The mammae or
teats of the female are located high on the sides, which
allows the young to suckle while in the water. When
pursued, nutria can swim long distances under water and
see well enough to evade capture.
The original range of
nutria was south of the equator in temperate South
America. This species has been introduced into other
areas, primarily for fur farming, and feral populations
can now be found in North America, Europe, the Soviet
Union, the Middle East, Africa, and Japan. M. c.
bonariensis was the primary subspecies of nutria
introduced into the United States.
Fur ranchers, hoping to
exploit new markets, imported nutria into California,
Washington, Oregon, Michigan, New Mexico, Louisiana,
Ohio, and Utah between 1899 and 1940. Many of the nutria
from these ranches were freed into the wild when the
businesses failed in the late 1940s. State and federal
agencies and individuals translocated nutria into
Alabama, Arkansas, Georgia, Kentucky, Maryland,
Mississippi, Oklahoma, Louisiana, and Texas, with the
intent that nutria would control undesirable vegetation
and enhance trapping opportunities. Nutria were also
sold as “weed cutters” to an ignorant public throughout
the Southeast. A hurricane in the late 1940s aided
dispersal by scattering nutria over wide areas of
coastal southwest Louisiana and southeast Texas.
Accidental and intentional
releases have led to the establishment of widespread and
localized populations of nutria in various wetlands
throughout the United States. Feral animals have been
reported in at least 40 states and three Canadian
provinces in North America since their introduction.
About one-third of these states still have viable
populations that are stable or increasing in number.
Some of the populations are economically important to
the fur industry. Adverse climatic conditions,
particularly extreme cold, are probably the main factors
limiting range expansion of nutria in North America.
Nutria populations in the United States are most dense
along the Gulf Coast of Louisiana and Texas (Fig. 2)
Nutria adapt to a wide variety of
environmental conditions and persist in areas previously
claimed to be unsuitable. In the United States, farm
ponds and other freshwater impoundments, drainage canals
with spoil banks, rivers and bayous, freshwater and
brackish marshes, swamps, and combinations of various
wetland types can provide a home to nutria. Nutria
habitat, in general, is the semiaquatic environment that
occurs at the boundary between land and permanent water.
This zone usually has an abundance of emergent aquatic
vegetation, small trees, and/or shrubs and may be
interspersed with small clumps and hillocks of high
ground. In the United States, all significant nutria
populations are in coastal areas, and freshwater marshes
are the preferred habitat.
almost entirely herbivorous and eat animal material
(mostly insects) incidentally, when they feed on plants.
Freshwater mussels and crustaceans are occasionally
eaten in some parts of their range. Nutria are
opportunistic feeders and eat approximately 25% of their
body weight daily. They prefer several small meals to
one large meal.
The succulent, basal
portions of plants are preferred as food, but nutria
also eat entire plants or several different parts of a
plant. Roots, rhizomes, and tubers are especially
important during winter. Important food plants in the
United States include cordgrasses (Spartina spp.),
bulrushes (Scirpus spp.), spikerushes (Eleocharis spp.),
chafflower (Alternanthera spp.), pickerelweeds (Pontederia
spp.), cattails (Typha spp.), arrowheads (Sagittaria spp.),
and flatsedges (Cyperus spp.). During winter, the bark
of trees such as black willow (Salix nigra) and
bald-cypress (Taxodium distichum) may be eaten. Nutria
also eat crops and lawn grasses found adjacent to
Because of their dexterous
forepaws, nutria can excavate soil and handle very small
food items. Food is eaten in the water; on feeding
platforms constructed from cut vegetation; at floating
stations supported by logs, decaying mats of vegetation,
or other debris; in shallow water; or on land. In some
areas, the tops of muskrat houses and beaver lodges may
also be used as feeding platforms.
Biology, Reproduction, and Behavior
In the wild,
most nutria probably live less than 3 years; captive
animals, however, may live 15 to 20 years. Predation,
disease and parasitism, water level fluctuations,
habitat quality, highway traffic, and weather extremes
affect mortality. Annual mortality of nutria is between
60% and 80%.
Predators of nutria
include humans (through regulated harvest), alligators
(Alligator mississippiensis), garfish (Lepisosteus spp.),
bald eagles (Haliaeetus leucocephalus), and other birds
of prey, turtles, snakes such as the cottonmouth (Agkistrodon
piscivorus), and several carnivorous mammals.
Nutria densities vary
greatly. In Louisiana, autumn densities of about 18
animals per acre (44/ha) have been found in floating
freshwater marshes. In Oregon, summer densities in
freshwater marshes may be 56 animals per acre (138/ha).
Sex ratios range from 0.6 to 1.6 males per female.
In summer, nutria live on
the ground in dense vegetation, but at other times of
the year they use burrows. Burrows may be those
abandoned by other animals such as armadillos (Dasypus
novemcinctus), beavers, and muskrats, or they may be dug
by nutria. Underground burrows are used by individuals
or multigenerational family groups.
Burrow entrances are
usually located in the vegetated banks of natural and
human-made waterways, especially those having a slope
greater than 45o. Burrows range from a simple, short
tunnel with one entrance to complex systems with several
tunnels and entrances at different levels. Tunnels are
usually 4 to 6 feet (1.2 to 1.8 m) long; however,
lengths of up to 150 feet (46 m) have been recorded.
Compartments within the tunnel system are used for
resting, feeding, escape from predators and the weather,
and other activities. These vary in size, from small
ledges that are only 1 foot (0.3 m) across to large
family chambers that measure 3 feet (0.9 m) across. The
floors of these chambers are above the water line and
may be covered with plant debris discarded during
feeding and shaped into crude nests.
In addition to using land
nests and burrows, nutria often build flattened circular
platforms of vegetation in shallow water. Constructed of
coarse emergent vegetation, these platforms are used for
feeding, loafing, grooming, birthing, and escape, and
are often misidentified as muskrat houses. Initially,
platforms may be relatively low and inconspicuous;
however, as vegetation accumulates, some may attain a
height of 3 feet (0.9 m).
Nutria breed in
all seasons throughout most of their range, and sexually
active individuals are present every month of the year.
Reproductive peaks occur in late winter, early summer,
and mid-autumn, and may be regulated by prevailing
Under optimal conditions,
nutria reach sexual maturity at 4 months of age. Female
nutria are polyestrous, and nonpregnant females cycle
into estrus (“heat”) every 2 to 4 weeks. Estrous is
maintained for 1 to 4 days in most females. Sexually
mature males can breed at any time because sperm is
produced throughout the year.
The gestation period for
nutria ranges from 130 to 132 days. A postpartum estrus
occurs within 48 hours after birth and most females
probably breed again during that time.
Litters average 4 to 5
young, with a range of 1 to 13. Litter sizes are
generally smaller during winter, in suboptimal habitats,
and for young females. Females often abort or assimilate
embryos in response to adverse environmental conditions.
Young are precocial and
are born fully furred and active. They weigh
approximately 8 ounces (227 g) at birth and can swim and
eat vegetation shortly thereafter. Young normally suckle
for 7 to 8 weeks until they are weaned.
Nutria tend to
be crepuscular and nocturnal, with the start and end of
activity periods coinciding with sunset and sunrise,
respectively. Peak activity occurs near midnight. When
food is abundant, nutria rest and groom during the day
and feed at night. When food is limited, daytime feeding
increases, especially in wetlands free from frequent
Nutria generally occupy a
small area throughout their lives. In Louisiana, the
home range of nutria is about 32 acres (13 ha). Daily
cruising distances for most nutria are less than 600
feet (183 m), although some individuals may travel much
farther. Nutria move most in winter, due to an increased
demand for food. Adults usually move farther than young.
Seasonal migrations of nutria may also occur. Nutria
living in some agricultural areas move in from marshes
and swamps when crops are planted and leave after the
crops are harvested.
Nutria have relatively
poor eyesight and sense danger primarily by hearing.
They occasionally test the air for scent. Although they
appear to be clumsy on land, they can move with
surprising speed when disturbed. When frightened, nutria
head for the nearest water, dive in with a splash, and
either swim underwater to protective cover or stay
submerged near the bottom for several minutes. When
cornered or captured, nutria are aggressive and can
inflict serious injury to pets and humans by biting and
Kinds of Damage
has been observed throughout their range. Most damage is
from feeding or burrowing. In the United States, most
damage occurs along the Gulf Coast of Louisiana and
Texas. The numerous natural and human-made waterways
that traverse this area are used extensively for travel
Burrowing is the most
commonly reported damage caused by nutria. Nutria are
notorious in Louisiana and Texas for undermining and
breaking through water-retaining levees in flooded
fields used to produce rice and crawfish. Additionally,
nutria burrows sometimes weaken flood control levees
that protect low-lying areas. In some cases, tunneling
in these levees is so extensive that water will flow
unobstructed from one side to the other, necessitating
their complete reconstruction.
Nutria sometimes burrow
into the Styrofoam flotation under boat docks and
wharves, causing these structures to lean and sink. They
may burrow under buildings, which may lead to uneven
settling or failure of the foundations. Burrows can
weaken roadbeds, stream banks, dams, and dikes, which
may collapse when the soil is saturated by rain or high
water or when subjected to the weight of heavy objects
on the surface (such as vehicles, farm machinery, or
grazing livestock). Rain and wave action can wash out
and enlarge collapsed burrows and compound the damage.
Nutria depredation on
crops is well documented. In the United States,
sugarcane and rice are the primary crops damaged by
nutria. Grazing on rice plants can significantly reduce
yields, and damage can be locally severe. Sugarcane
stalks are often gnawed or cut during the growing
season. Often only the basal internodes of cut plants
are eaten. Other crops that have been damaged include
corn, milo (grain sorghum), sugar and table beets,
alfalfa, wheat, barley, oats, peanuts, various melons,
and a variety of vegetables from home gardens and truck
Nutria girdle fruit, nut,
and shade trees and ornamental shrubs. They also dig up
lawns and golf courses when feeding on the tender roots
and shoots of sod grasses. Gnawing damage to wooden
structures is common. Nutria also gnaw on styrofoam
floats used to mark the location of traps in commercial
At high densities and
under certain adverse environmental conditions, foraging
nutria can significantly impact natural plant
communities. In Louisiana, nutria often feed on seedling
baldcypress and can cause the complete failure of
planted or naturally-regenerated stands. Overutilization
of emergent marsh plants can damage stands of desirable
vegetation used by other wildlife species and aggravate
coastal erosion problems by destroying vegetation that
holds marsh soils together. Nutria are fond of grassy
arrowhead (Sagittaria platyphylla) tubers and may
destroy stands propagated as food for waterfowl in
Nutria can be infected
with several pathogens and parasites that can be
transmitted to humans, livestock, and pets. The role of
nutria, however, in the spread of diseases such as
equine encephalomyelitis, leptospirosis, hemorrhagic
septicemia (Pasteurellosis), paratyphoid, and
salmonellosis is not well documented. They may also host
a number of parasites, including the nematodes and blood
flukes that cause “swimmer’s-itch” or “nutria-itch” (Strongyloides
myopotami and Schistosoma mansoni), the protozoan
responsible for giardiasis (Giardia lamblia), tapeworms
(Taenia spp.), and common liver flukes (Fasciola
hepatica). The threat of disease may be an important
consideration in some situations, such as when livestock
drink from water contaminated by nutria feces and urine.
The ranges of
nutria, beavers, and muskrats overlap in many areas and
damage caused by each may be similar in appearance.
Therefore, careful examination of sign left at the
damage site is necessary to identify the responsible
On-site observations of
animals and their burrows are the best indicators of the
presence of nutria. Crawl outs, slides, trails, and the
exposed entrances to burrows often have tracks that can
be used to identify the species. The hind foot, which is
about 5 inches (13 cm) long, has four webbed toes and a
free outer toe. A drag mark left by the tail may be
evident between the footprints (Fig. 3).
Droppings may be found
floating in the water, along trails, or at feeding
sites. These are dark green to almost black in color,
cylindrical, and approximately 2 inches (5 cm) long and
1/2 inch (1.3 cm) in diameter. Additionally, each
dropping usually has deep, parallel grooves along its
entire length (Fig. 4).
Trees girdled by nutria
often have no tooth marks, and bark may be peeled from
the trunk. The crowns of seedling trees are usually
clipped (similar to rabbit [Sylvilagus spp.] damage) and
discarded along with other woody portions of the plant.
In rice fields, damage
caused by nutria, muskrats, and Norway rats (Rattus
norvegicus) can be confused. Nutria and muskrats damage
rice plants by clipping stems at the water line in
flooded fields; Norway rats reportedly clip stems above
the surface of the water (E. A. Wilson, personal
Nutria are protected as
furbearers in some states or localities because they are
economically important. Permits may be necessary to
control animals that are damaging property. In other
areas, nutria have no legal protection and can be taken
at any time by any legal means. Consequently, citizens
experiencing problems with nutria should be familiar
with local wildlife laws and regulations. Complex
problems should be handled by professional wildlife
damage control specialists who have the necessary
permits and expertise to do the job correctly. Your
state wildlife agency can provide the names of qualified
wildlife damage control specialists and information on
pertinent laws and regulations.
Prevention and Control Methods
Preventive measures should
be used whenever possible, especially in areas where
damage is prevalent. When control is warranted, all
available techniques should be considered before a
control plan is implemented. The objective of control is
to use only those techniques that will stop or alleviate
anticipated or ongoing damage or reduce it to tolerable
levels. In most cases, successful control will depend on
integrating a number of different techniques and
Timing and location of
control activities are important factors governing the
success or failure of any control project. Control in
sugarcane, for example, is best applied during the
growing season, after damage has started. At this time,
nutria in affected areas are relatively stationary and
concentrated in drainages adjacent to fields.
Conversely, efforts to protect rice field levees or the
shorelines of southern lakes and ponds should be
initiated during the winter when animals are mobile and
concentrated in Fig. 4. Nutria dropping in relation to a
2-inch (5.1-cm) camera lens cover. Note longitudinal
grooves major ditches and other large bodies of along
the length of the dropping. water.
Nutria are best controlled
where they are causing damage or where they are most
active. Baiting is sometimes used to concentrate nutria
in specific locations where they can be controlled more
easily. After the main concentrations of nutria are
removed, control efforts should be directed at removing
and other structures can reduce nutria damage, but high
costs usually limit their use. As a general rule,
barriers are too expensive to be used to control damage
to agricultural crops. Low fences (about 4 feet [1.2 m])
with an apron buried at least 6 inches (15 cm) have been
used effectively to exclude nutria from home gardens and
lawns. Sheet metal shields can be used to prevent
gnawing damage to wooden and styrofoam structures and
trees. Barriers constructed of sheet metal can be
expensive to erect and unsightly.
Protect baldcypress and
other seedlings with hardware cloth tubes around
individual plants or wire mesh fencing around the
perimeter of a stand. Extensive use of these is neither
practical nor cost-effective. Plastic seedling
protectors are not effective in controlling damage to
baldcypress seedlings because nutria can chew through
Sheet piling, bulkheads,
and riprap can effectively protect stream banks from
burrowing nutria. Installation requires heavy equipment
and is expensive. Use is usually restricted to
industrial or commercial applications.
Cultural Methods and
Land that is
well-drained and free of dense, weedy vegetation is
generally unattractive to nutria. Use of other good
farming practices, such as precision land leveling and
weed management, can minimize nutria damage in
Draining and Grading.
Any drainage that holds water can be used by nutria as a
travel route or home site. Consequently, eliminate
standing water in drainages to reduce their
attractiveness to nutria. This may be extremely
difficult or impossible to accomplish in low-lying areas
near coastal marshes and permanent bodies of water.
Higher sites, such as those used for growing sugarcane
and other crops, are better suited for this type of
On poorly drained soils,
contour small ditches to eliminate low spots and sills
and enhance rapid drainage. Use precision leveling on
well-drained soils to eliminate small ditches that are
occasionally used by nutria.
Grading and bulldozing can
destroy active burrows in the banks of steep-sided
ditches and waterways. In addition, contour bank slopes
at less than 45o to discourage new burrowing. Sculpting
rice field levees to make them gently sloping is
similarly effective. Continued deep plowing of land
undermined by nutria can destroy shallow burrow systems
and discourage new burrowing activity.
Eliminate brush, trees, thickets, and weeds from fence
lines and turn rows that are adjacent to ditches,
drainages, waterways, and other wetlands to discourage
nutria. Burn or remove cleared vegetation from the site.
Brush piles left on the ground or in low spots can
become ideal summer homes for nutria.
Manipulation. Many low-lying areas along the Gulf
Coast are protected by flood control levees and pumps
that can be used to manipulate water levels. By dropping
water levels during the summer, stressful drought
conditions that cause nutria to concentrate in the
remaining aquatic habitat can be simulated, thus
increasing competition for food and space, exposure to
predators, and emigration to other suitable habitat.
Raising water levels in winter will force nutria out of
their burrows and expose them to the additional stresses
of cold weather. Water level manipulation is expensive
to implement and has not yet been proven to be
effective. Nevertheless, this method should be
considered when a comprehensive nutria control program
is being developed.
Other Cultural Methods.
Alternate field and garden sites should be considered in
areas where nutria damage has occurred on a regular
basis. New fields, gardens, and slab-on-grade buildings
should be located as far as possible from drainages,
waterways, and other water bodies where nutria live.
seedlings are less susceptible to damage by nutria than
those planted in the spring. For this reason, plant
unprotected seedlings in the early fall when alternative
natural foods are readily available.
Nutria are wary
creatures and will try to escape when threatened. Loud
noises, high pressure water sprays, and other types of
harassment have been used to scare nutria from lawns and
golf courses. The success of this type of control is
usually short-lived and problem animals soon return.
Consequently, frightening as a control technique is
neither practical nor effective.
repellents for nutria are currently registered. Other
rodent repellents (such as Thiram) may repel nutria, but
their effectiveness has not been determined. Use of
these without the proper state and federal pesticide
registrations is illegal.
Zinc phospide is the only toxicant that is registered
for controlling nutria. Zinc phosphide is a Restricted
Use Pesticide that can only be purchased and applied by
certified pesticide applicators or individuals under
their direct supervision. It is a grayish-black powder
with a heavy garlic-like smell and is widely used for
controlling a variety of rodents. When used properly,
zinc phosphide poses little hazard to nontarget species,
humans, pets, or livestock.
is highly toxic to wildlife and humans, so all
precautions and instructions on the product label should
be carefully reviewed, understood, and followed
precisely. Use an approved respirator and wear
elbow-length rubber gloves when handling this chemical
to prevent accidental poisoning. Mix and store baits
treated with zinc phosphide only in well-ventilated
areas to reduce exposing humans to chemical fumes and
dust. When possible, mix zinc phosphide at the baiting
site to avoid having to store and transport treated
baits. Never transport mixed bait or open zinc phosphide
containers in the cab of any vehicle. Store unused zinc
phosphide in a dry place in its original watertight
container because moisture causes it to deteriorate.
Immediately wash off any zinc phosphide that gets on the
Past studies have shown
that zinc phosphide can kill over 95% of the nutria
present along waterways when applied to fresh baits at a
0.75% (7,500 ppm) rate. Today, the use of zinc phosphide
at this concentration is illegal. Federal and state
registrations, however, allow lower rates to be used.
For example, the label held by USDA-APHIS-ADC (EPA Reg.
No. 56228-9) allows for a maximum 0.67% (6,700 ppm)
treatment rate. At this rate, approximately 94 pounds
(42.7 kg) of bait can be treated with 1 pound (0.4 kg)
of 63.2% zinc phosphide concentrate.
Where to Bait.
The best places to bait nutria are in waterways, ponds,
and ditches where permanent standing water and recent
nutria sign are found. Baiting in these areas increases
efficiency and reduces the likelihood that nontarget
animals will be affected. Small chunks of unpeeled
carrots, sweet potatoes, watermelon rind, and apples can
be used as bait.
The best baiting stations
for large waterways are floating rafts spaced 1/4 to 1/2
mile (0.4 to 0.8 km) apart throughout the damaged area.
In ponds, use one raft per 3 acres (1.2 ha). Rafts
measuring 4 feet (1.2 m) square or 4 x 8 feet (1.2 x 2.4
m) are easily made from sheets of 3/8-to 3/4-inch (1.0-
to 1.9-cm) exterior plywood and 3-inch (7.6-cm)
styrofoam flotation. Install a thin wooden strip around
the perimeter of the raft’s surface to keep bait from
rolling into the water. The raft should float 1 to 4
inches (2.5 to 10.2 cm) above the surface and should be
anchored to the bottom with a heavy weight or tied to
the shore (Fig. 5).
In small ditches or areas
where nutria densities are low, use 6-inch (15.2-cm)
square floating bait boards made of wood and styrofoam,
in lieu of rafts (Fig. 5). These can be maintained in
place with a long slender anchoring pole made of bamboo,
reed, or other suitable material that is placed through
a hole in the center of the platform. This allows the
board to move up and down as water levels change. Attach
baits to small nails driven into the surface of the
platform. Bait boards should be spaced 50 to 100 feet
(15.2 to 30.5 m) apart in areas where nutria are active.
Other natural sites
surrounded by water can also be baited for nutria. Small
islands, exposed tree stumps, floating logs, and feeding
platforms are excellent baiting sites. Avoid placing
baits on muskrat houses and beaver lodges. Baits can be
attached to trees, stumps, or other structures with
small nails and should be kept out of the water.
Baiting on the ground
should only be used when water sites are unsuitable or
lacking. Ground baiting is justified and effective when
eliminating the last few nutria in a local population.
Use care when ground baiting because baits may be
accessible to nontarget animals and humans. Place ground
baits near sites of nutria activity, such as trails and
entrances to burrows.
Prebaiting is a crucial step when using zinc phosphide
because it leads to nutria feeding at specific sites on
specific types of food (such as the baits; carrots or
sweet potatoes are preferred). Nutria tend to be
communal feeders, and if one nutria finds a new feeding
spot, other nutria in the area will also begin feeding
To prebait, lightly coat
small (approximately 2-inch [5.1-cm] long) chunks of
untreated bait with corn oil. Place the bait at each
baiting station in late afternoon, and leave it
overnight. Use no more than 10 pounds (4.5 kg) of bait
per raft, 4 pieces of bait per baiting board, or 2 to 5
pieces at other sites at one time. Prebaiting should
continue at least 2 successive nights after nutria begin
feeding at a baiting site. Large (more than 1 week) gaps
in the prebaiting sequence necessitate that the process
be started over.
Observations of prebaited
sites will help you decide how the control program
should proceed. If nontarget animals are feeding at
these sites (as determined by sign or actual
observations of animals), then prebaiting should start
over at another location. Prepare and apply zinc
phosphide-treated baits when nutria become regular users
of prebaited baiting stations and nontarget animals are
not a problem.
Phosphide. Prepare zinc phosphide baits as
needed to prevent deterioration. Treated baits are
prepared in 10-pound (4.5-kg) batches (enough to treat
one raft) by using the following ingredients: 10 pounds
(4.5 kg) of bait (carrots or sweet potatoes are
preferred), prepared as for prebaiting; 1 fluid ounce or
2 tablespoons (30 ml) of corn oil; and 1.7 ounces or 7.5
tablespoons (48.2 g) of 63.2% zinc phosphide
To prepare treated baits,
add corn oil to the bait in a 5 gallon (18.9 l) plastic
or metal container. Stir the mixture until the bait is
lightly coated with corn oil. Sprinkle zinc phosphide
over the mixture and stir until the bait is uniformly
coated. Treated baits have a shiny black appearance and
should be dried for about 1 hour in a well-ventilated
area until the color changes to a dull gray. Properly
dried baits are weather-resistant and remain toxic until
they deteriorate. Although treated baits can survive
light rain, they should not be used when heavy rains are
expected or on open water that is subject to heavy wave
The amount of untreated
bait eaten the last night of prebaiting determines how
much treated bait should be used on the first night.
When all or most of the untreated prebait is gone from
baiting stations by morning, the same amount of treated
bait is used on the stations the following night (e.g.,
up to 10 pounds [4.5 kg] per raft, 4 pieces per baiting
board, and 2 to 5 pieces at other sites). When smaller
quantities are eaten, reduce the amount of treated bait
that is used per station proportionately. When only a
few pieces of prebait on a raft are eaten, the raft
should be removed and replaced with several scattered
The quantity of treated
bait eaten each treatment night is the quantity that
should be put out the following afternoon. Continue
baiting until no more bait is being taken. Most nutria
can be controlled after 4 nights of baiting. When
densities are high, control may require more time.
Procedures. Usually only 25% of the poisoned
nutria die where they can be found. Many nutria die in
dens, dense vegetation, and other inaccessible areas.
Carcasses of nutria killed with zinc phosphide should be
collected as soon as possible and disposed of by deep
burial or burning to prevent exposure of domestic and
wild scavengers to undigested stomach material
containing zinc phosphide. Dispose of any leftover
treated bait in accordance with label directions.
Cessation of damage is the
best indicator that zinc phosphide is controlling
problem animals. You can quantify the reduction in
nutria activity by putting out untreated bait at baiting
stations after the last application of zinc phosphide.
The amount eaten at this time is compared to the amount
of bait eaten on the last night of prebaiting.
fumigants are registered for controlling burrowing
rodents but none are registered for use against nutria.
Some, such as aluminum phosphide, may have potential as
nutria control agents, but their efficacy has not been
scientifically demonstrated. Carbon monoxide gas pumped
into dens has reportedly been used to kill nutria, but
this method is neither practical nor legal because it is
not registered for this purpose.
Harvest. Damage to crops, levees, wetlands, and other
resources is minimal in areas where nutria are harvested
by commercial trappers. The commercial harvest of nutria
on private and public lands should be encouraged as part
of an overall program to manage nutria-caused damage.
Landowners may be able to obtain additional information
on nutria management, trapping, and a list of licensed
trappers in their area from their state wildlife agency.
Leghold traps are the most commonly used traps for
catching nutria. Double longspring traps, No. 11 or 2,
are preferred by most trappers; however, the No. 1 1/2
coilspring, No. 3 double longspring, or the soft-catch
fox trap can also be used effectively. Legholds are more
efficient and versatile than body-grip traps and are
highly recommended for nutria control work. Leghold
traps should be used with care to prevent injury to
children and pets.
Several ways of setting
leghold traps are effective. Set traps just under the
water where a trail enters a ditch, canal, or other body
of water. Make trail sets by placing a trap offset from
the trail’s center line so that nutria are caught by the
foot. Traps can be lightly covered with leaves or other
debris to hide them, but nutria are easily captured in
Bait can be used to lure
nutria to leghold sets. Nutria use their teeth to pick
up large pieces of food; therefore, bait should be
placed beside, rather than inside, the trap jaws.
Leghold traps are also effective when set on floating
rafts that have been prebaited for a short period of
Use drowning sets when
deep water is available. Otherwise, stake leghold traps
to the ground, or anchor them to solid objects in the
water or on land (such as floating logs, stumps, or
trees and shrubs). Nutria caught in non-drowning leghold
sets should be humanely dispatched with a shot or hard
blow to the head. Nontarget animals should be released.
Nutria are easily captured in single-or double-door live
traps that measure 9 x 9 x 32 inches (22.8 x 22.8 x 81.3
cm) or larger.
Use these when leghold and
body-grip traps cannot be set or when animals are to be
translocated. Bait live traps with sweet potatoes and
carrots and place them along active trails or wherever
nutria or their sign are seen. A short line of baits
leading to the entrance of a live trap will increase
capture success. Live traps placed on floating rafts
will effectively catch nutria but prebaiting is
necessary. A large raft can hold up to 8 traps. Unwanted
nutria should be destroyed with a shot or blow to the
head. Nontarget animals should be released.
Floating, drop-door live
traps catch nutria but are bulky and cumbersome to use.
The same is true for expensive suitcase-type beaver
traps. Unwary nutria can be captured using a
long-handled dip net. This method should only be used by
trained damage control professionals who should take
special precautions to prevent being bitten or clawed
(Fig. 6). Live nutria can be immobilized with an
injection of ketamine hydrochloride. Funnel traps are
not effective for controlling nutria.
The Conibear® trap, No. 220-2, is the most commonly used
body-gripping trap for controlling nutria. Nos. 160-2
and 330-2 Conibear® traps can also be used. Place sets
in trails, at den entrances, in culverts, and in narrow
waterways. Large body-grip traps can be dangerous and
should be handled with extreme caution. These traps
should not be set in areas frequented by children, pets,
or desirable wildlife species.
Use locking snares to catch nutria when other traps
cannot be set. Snares are relatively easy to set, safer
than leghold and body-grip traps, and almost invisible
to the casual observer. Snares constructed with
3/32-inch (0.2-cm) diameter, flexible (7 x 7-winding)
stainless steel or galvanized aircraft cable are
suitable for catching nutria. Ready-made snares and
components (for example, cable, one-way cable locks,
swivels, and cable stops) for making homemade snares can
be purchased from trapping suppliers.
Place set snares in trails
and other travel routes, feeding lanes, trails, and bank
slides. Snares do not kill the animals they catch, so
anchor the snare securely. Check snares frequently
because they are often knocked down by nutria and other
animals. Snared nutria should be dispatched with a shot
or blow to the head. Release any nontarget animals that
Shooting can be
used as the primary method of nutria control or to
supplement other control techniques. Shooting is most
effective when done at night with a spotlight, however,
night shooting is illegal in many states and should not
be done until proper permits have been obtained. Once
shooting has been approved by the proper authorities,
nutria can be shot from the banks of waterways and other
bodies of water or from boats. In some cases, 80% of the
nutria in an area can be removed by shooting with a
shotgun or small caliber rifle, such as the .22 rimfire.
Care should be taken when shooting over open water to
prevent bullets from ricocheting.
Shooting at Bait
Stations. Baits can attract large numbers of
nutria to floating rafts, baiting boards, and other
areas where they can be shot. Shooting from dusk to
about 10:00 p.m. for 3 consecutive nights is effective
once a regular feeding pattern has been established.
Feeding sites should be lit continuously by a spotlight
and easily visible to the shooter from a vehicle or
other stationary blind. At night, nutria can be located
by their red-shining eyes and the V-shaped wake left by
swimming animals. As many as 4 to 5 nutria per hour may
be taken by this method. Shooters should wait 2 to 3
weeks before shooting nutria at the same site again.
Shooting can also be done in the late afternoon or early
evening from a small boat paddled slowly along waterways
and large ditches or along the shores of small lakes and
ponds. Nutria are especially vulnerable to this method
when water levels are extremely high or vegetative cover
is scarce. At times, animals can be stimulated to
vocalize or decoyed to a boat or blind by making a “maw”
call, which imitates the nutria’s nocturnal feeding and
assembly call. This call can be learned from someone who
knows it or by listening to nutria vocalizations at
night. Nutria become wary quickly, so limit shooting to
no more than 3 nights, followed by 2 to 3 weeks of no
Nutria can be shot by slowly stalking along the banks of
ditches and levees; this can be an effective control
method where nutria have not been previously harassed.
Unlike night shooting from a boat or blind, bank
shooting is most effective at twilight, both in the
evening and morning. Several nutria can usually be shot
the first night, however, success decreases with each
successive night of shooting. Daytime shooting from the
bank of a waterway is effective in some situations.
of Damage and Control
Nutria can have either
positive or negative values. They are economically
important furbearers when their pelts provide income to
commercial trappers. Conversely, they are considered
pests when they damage property.
From 1977 to 1984, an
average of 1.3 million nutria pelts were harvested
annually in the United States. Based on prices paid to
Louisiana trappers during this period, these pelts were
worth about $7.3 million.
The estimated value of
sugarcane and rice damaged by nutria each year has
ranged from several thousand dollars to over a million
dollars. If losses of other resources are added to this
amount, the estimated average loss would probably exceed
$1 million annually.
Management plans developed
for nutria should be comprehensive and should consider
the needs of all stakeholders. Regulated commercial
trapping should be an integral part of any management
scheme because it can provide continuous, long-term
income to trappers; maintain acceptable nutria
densities; and reduce damage to tolerable levels.
The value of the protected
resource must be compared with the cost of control when
determining whether nutria control is economically
feasible. Most people will not control nutria if costs
exceed the value of the resource being protected or if
control will adversely impact income derived from
trapping. Of course, there are exceptions, especially
when the resource has a high sentimental or aesthetic
value to the owner or user.
This chapter is a revision
of an earlier chapter written by Evans (1983). Kinler et
al. (1987) and Willner (1982) were the primary sources
consulted for biological information on nutria.
Figures 1 and 3 by Peggy
A. Duhon of Lafayette, Louisiana.
Figure 2 from Willner
(1982) and reprinted with permission of The Johns
Hopkins University Press, Baltimore, Maryland.
Harland D. Guillory, Dr.
Robert B. Hamilton, and E. Allen Wilson reviewed the
manuscript and provided valuable comments and
For Additional Information
Baker, S. J., and C. N. Clarke. 1988. Cage trapping
coypus (Myocastor coypus) on baited rafts. J. Appl.
Conner, W. H., and J. R.
Toliver. 1987. The problem of planting cypress in
Louisiana swamplands when nutria (Myocastor coypus) are
present. Proc. Eastern Wildl. Damage Control Conf.
Conner, W. H., and J. R.
Toliver. 1987. Vexar seedling protectors did not reduce
nutria damage to planted baldcypress seedlings. Tree
Planters’ Notes 38:26-29.
Evans, J. 1970. About
nutria and their control. US Dep. Inter., Bureau Sport
Fish. Wildl., Resour. Publ. No. 86. 65 pp.
Evans, J. 1983. Nutria.
Pages B-61 to B-70 in R.M. Timm, ed. Prevention and
control of wildlife damage, Coop. Ext. Serv., Univ.
Evans, J., J. O. Ells, R.
D. Nass, and A. L. Ward. 1972. Techniques for capturing,
handling, and marking nutria. Trans. Annual Conf.
Southeast. Assoc. Game Fish Comm. 25:295-315.
Falke, J. 1988.
Controlling nutria damage. Texas An. Damage Control Serv.
Leaflet 1918. 3 pp.
Kinler, N. W., G.
Linscombe, and P. R. Ramsey. 1987. Nutria. Pages 331-343
in M. Novak, J. A. Baker, M. F. Obbard, and B. Malloch,
eds. Wild furbearer management and conservation in North
America. Ministry of Natural Resources, Ontario.
Wade, D. A., and C. W.
Ramsey. 1986. Identifying and managing aquatic rodents
in Texas: beaver, nutria, and muskrats. Texas Agric.
Ext. Serv. Bull. 1556. 46 pp.
Willner, G. R. 1982.
Nutria. Pages 1059-1076 in J. A. Chapman and G. A.
Feldhamer, eds. Wild mammals of North America: biology,
management, and economics. The Johns Hopkins Univ.
Press, Baltimore, Maryland.
Scott E. Hygnstrom Robert
M. Timm Gary E. Larson
PREVENTION AND CONTROL OF
WILDLIFE DAMAGE — 1994
Division Institute of Agriculture and Natural Resources
University of Nebraska -Lincoln
United States Department
of Agriculture Animal and Plant Health Inspection
Service Animal Damage Control
Great Plains Agricultural
Council Wildlife Committee