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Figure
1. Opossums measure 2 to 3 feet
in length, a third of which is a round, scaly, sparsely
haired tail. The head is conical, tapering to a slender,
elongated snout tipped by a pink-colored nose. The face
is light gray to white, whereas the general color of
the fur from neck to rump is grayish white. Because
of its body shape, a small opossum is sometimes mistaken
for a large rat. (Photo by Kim Chandler.) |
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Prior to European
settlement of North America, the Virginia opossum (Didelphis
virginianus, Fig. 1) was found only in Central America and the
southeastern United States. During the 1900s, its range expanded
northward and westward.
Virginia opossums,
also known as “possums,” first arrived in Washington
in the early 1900s as pets and novelties. Some of these animals,
or their offspring, later escaped from captivity or were intentionally
released.
With few natural
predators, the absence of hunting, and an abundance of food and
shelter, opossums have adapted well to living close to people in
urban and suburban environments. Except for higher elevations, opossums
now occupy most human-occupied habitats in western Washington.
Opossums are
marsupials (mammals with a pouch in which they carry their young),
a primitive group of mammals found most commonly in Australia. Kangaroos,
koalas, and wombats are other well known marsupials. Opossums are
the only marsupials in North America. All other mammals are placentals,
which means their young develop within a saclike membrane called
the placenta inside the mother’s uterus, rather than in an
exterior pouch.
In Australia
and elsewhere, many species of marsupial have been out-competed
and even driven to extinction by more modern mammals. Yet, the opossum
has adapted to the changing environment in the Western Hemisphere,
and continues to thrive.
Opossums are
inhibited animals, especially in daylight or under artificial light,
but are by no means stupid. Results from some learning and discrimination
tests rank opossums above dogs and more or less on a par with pigs
in intelligence.
Facts
about Washington’s Opossums
Food and
Feeding Habitats
- Opossums
lived during the time of the dinosaurs and one reason for their
continued survival is their ability to eat nearly anything.
- Foods
include fruits, nuts, grains, insects, slugs, snakes, frogs,
birds, bird eggs, shellfish, mice, and carrion (dead animals).
- Around
human habitation, opossums also eat garbage, pet food, birdseed,
poultry, and handouts.
- A study
of Portland Oregon’s opossum population found that small
mammals (dead and alive) were the most important food in winter
and spring, slugs in summer, and fruits in fall.
- Because
opossums eat many road-killed animals, including other opossums,
they often become road kill themselves.
- Because
opossums accumulate little body fat for winter and don’t
store food, they must forage year-round.
Den Sites
- Opossums
will den nearly anywhere that is dry, sheltered, and safe. Den
sites include burrows dug by other mammals, rock crevices, hollow
stumps, logs and trees, woodpiles, and spaces in or under buildings.
- Their
fur doesn’t provide much insulation, so opossums fill
their dens with dried leaves, grass, and other available soft
material to form well-insulated nests. Nest materials are carried
in their coiled tail.
- To avoid
predators, opossums move to a different den every few days.
(A male opossum followed by radio tracking used 19 different
dens in five months.)
- A female
with young or an opossum “holed up” during a cold
spell will use the same den for a greater length of time.
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Figure
2. Young opossums ride on their mother’s back with
their feet and tail firmly attached to her fur.
(From Christensen and Larrison, Mammals of the
Pacific Northwest: A Pictorial Introduction.) |
Reproduction
- Opossums
are successful as a species due in part to the size and frequency
of litters.
- The breeding
season begins as early as January and may continue to mid-November.
- Being
marsupials, opossums give birth to undeveloped young. Only 12
days following breeding, five to ten bumblebee-sized pups crawl
into their mother’s pouch, where each firmly attaches
to a teat.
- Opossum
pups find nourishment, warmth, and safety in the pouch. When
closed, it is so well sealed that if the female swims, the pups
remain dry.
- At 60
to 70 days old, the house mouse-size young begin to leave the
pouch for brief periods, returning to suckle.
- At 80
to 90 days old, the young begin to ride on their mother’s
back with their feet and tail firmly attached to her fur (Fig.
2). (Contrary to myth, a female opossum never carries her young
on her tail.)
- At 3½
months of age, the young begin to leave the den to feed on their
own, and soon disperse to establish their own territories.
Mortality
and Longevity
- Opossums
have high mortality rates at all ages. They are killed by dogs,
coyotes, foxes, raccoons, bobcats, eagles, hawks, and owls,
with young opossums being the most vulnerable.
- Car kills
in the fall and in winter conditions account for many opossum
deaths.
- Opossums
rarely live a full two years in the wild.
Viewing
Opossums
Opossums are
nocturnal, spending the day in dens or other protected spots.
However, they can be seen at any time of day, especially in winter
when food is scarce. At night, opossums forage in areas near their
current dens, but can travel up to 2 miles in search of food.
Opossums
are solitary animals, and except during breeding season or a female
with her young, they are rarely seen together. Opossums do not
hibernate.
Although
they can climb and are good swimmers, opossums prefer to amble
about on the ground. With a top speed of about 4 miles per hour,
when “running,” opossums appear to be walking quickly,
with the tail rotating in circles for balance. When idle, opossums
constantly groom themselves, much as house cats do.
A nighttime
walk along a path bordering a stream or wetland, or down an alley
lined with trashcans, will occasionally turn up an opossum searching
for food. Strong but not agile climbers, opossums can be observed
climbing trees to escape, search for food, rest, or to look for
dens. Their tails are able to wrap around and grasp tree limbs
and can support the animal’s full weight for short periods.
(Contrary to myth, opossums do not hang upside down by their tails
when sleeping.)
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Figure
3. The opossum’s front tracks are about 2 inches in
diameter and hind tracks are slightly larger. The opossum’s
long tail often leaves drag marks in snow or mud.
(Drawings by Kim A. Cabrera.) |
Trails
Opossums readily
use trails made by other wildlife or humans near creeks, ravines,
and wetlands. Like raccoons and foxes, opossums use culverts as
a safe way to cross under highways and roadways.
In developed
areas, trails occur along buildings and fences. Wear marks and
hairs may be found around the edges of entry points where opossums
are entering a building or crawling under a fence. Opossum hair
is long and silver to gray in color.
Tracks
Tracks can
be found in mud, snow, or fine soil; also on deck railings, downspouts,
and other surfaces that opossums use to gain access to structures
(Fig. 3). The opossum’s opposable hind thumbs create a unique
print, pointing as much as 90 degrees away from the direction
of travel.
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Figure
4. Opossum droppings may resemble the droppings of house
cats and small domestic dogs, coyotes, and foxes.
(Photo from Acorn Naturalists.) |
Droppings
Opossum droppings
are not easily found, but can be seen along trails they use and
near favorite feeding spots. Opossum droppings vary in appearance
according to the animal’s diet and may resemble the droppings
of house cats and small domestic dogs, coyotes, and foxes (Fig.
4). Firm droppings are pointed on the ends and 1 to 3 inches long.
Calls
Opossums are
among the most silent animals that live in Washington, but when
frightened or threatened they growl and hiss.
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| Figure
5. When caught out in the daylight with little chance
of escape, or when attacked, the opossum will “play
possum.” |
The opossum
is a slow runner and when threatened will usually growl, hiss,
and bare its teeth or try to escape by climbing the nearest
tree. However, when caught out in the daylight with little chance
of escape, or when attacked, the opossum will “play possum.”
This is a surprisingly effective defense commonly seen in insects.
In such cases the opossum will fall on its side, curl its body,
open its drooling mouth, and excrete droppings—all to
give the appearance of being dead.
While the opossum is in this state, which lasts several minutes
or several hours, no amount of prodding will produce a response.
Though it appears to be in a catatonic state, its metabolic
processes are as high as when the animal is fully alert.
When
the opossum believes the danger has passed, it will begin
to wiggle its ears in an effort to pick up sounds. If it thinks
the danger has passed, it will pick up its head and look around.
If danger persists, the opossum will play dead again. |
Preventing
Conflicts
In urban areas,
opossums are beneficial as rodent and carrion eaters. They also
clean up uneaten food that might otherwise attract mice and rats.
However, in rural areas the impact of non-native opossums preying
upon native invertebrates, small mammals, amphibians, reptiles,
ground-nesting birds, nestlings, and eggs is of concern to wildlife
biologists.
As long as
they are kept out of human homes, not cornered, and their interaction
with pets is limited, opossums are not dangerous. If an opossum
finds its way into your house, stay calm, close surrounding interior
doors, leave the room, and let the animal find its own way out
through the pet door or an open door or window. If necessary,
gently use a broom to coral the opossum outside. Do not corner
an opossum, thereby forcing it to defend itself.
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Figure
6. Their 50 teeth (more than any other mammal in North America)
give opossums a menacing look when threatened.
(From Verts and Carraway, Land Mammals of Oregon.)
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If the opossum
appears sick or injured, call a wildlife rehabilitator or your
local wildlife office (see Wildlife
Rehabilitators and Wildlife Rehabilitation).
Although
generally gentle and placid, opossums have 50 teeth and will use
them to protect themselves, or their young (Fig. 6). So avoid
close encounters.
An opossum’s
search for food may lead it to a vegetable garden, garbage can,
or chicken coop. Its search for a den site may lead it to an attic,
chimney, or crawl space. The most effective way to prevent conflicts
is to modify the habitat around your home so as not to attract
opossums.
Recommendations
on how to do this are given below:
Don’t
feed opossums. Feeding opossums may create undesirable situations
for you, your children, neighbors, pets, and the opossums themselves.
Opossums that are fed by people often lose their fear of humans
and may become aggressive when not fed as expected. Artificial
feeding also tends to concentrate opossums in a small area; overcrowding
can spread diseases and parasites. Finally, these hungry visitors
might approach a neighbor who doesn’t share your appreciation
of the animals. The neighbor might choose to remove these opossums,
or have them removed.
Don’t
give opossums access to garbage. Keep your garbage can lid
on tight by securing it with rope, chain, bungee cords, or weights.
Better yet, buy garbage cans with clamps or other mechanisms that
hold lids on. To prevent tipping, secure side handles to metal
or wooden stakes driven into the ground. Or keep your cans in
tight-fitting bins, a shed, or a garage. Put garbage cans out
for pickup in the morning, after opossums have returned to their
resting areas.
Feed dogs
and cats indoors and keep them in at night. If you must feed
your pets outside, do so in late morning or at midday, and pick
up food, water bowls, leftovers, and spilled food well before
dark every day.
Keep pets
indoors at night. If cornered, opossums may attack dogs and
cats. Bite wounds from opossums can result in fractures and disease
transmission.
Prevent
opossums from entering pet doors. Keep indoor pet food and
any other food away from a pet door. Lock the pet door at night.
If it is necessary to have it remain open, put an electronically
activated opener on your pet’s collar. Note: Floodlights
or motion detector lights placed above the pet door to scare opossums
are not long-term solutions.
Put food
in secure compost containers and clean up barbecue areas.
Don’t put food of any kind in open compost piles; instead,
use a securely covered compost structure or a commercially available
opossums-proof composter to prevent attracting opossums and getting
exposed to their droppings. A covered worm box is another alternative.
If burying food scraps, cover them with at least 8 inches of soil
and don’t leave any garbage above ground in the area—including
the stinky shovel. Cover the burial site with heavy wire mesh
and a weight as further prevention.
Clean barbecue
grills and grease traps thoroughly following each use.
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| Figure
7. Opossums access to rooftops can be eliminated by installing
sheets of aluminum flashing, at least 3 feet square, around
the corners of buildings. |
Figure
8. Commercially available metal or plastic spikes can
help keep opossums off of buildings.
(Drawings
by Jenifer Rees.) |
Eliminate
access to denning sites. Opossums commonly use chimneys, attics,
and spaces under houses, porches, and sheds as den sites. Close
any potential entries with ¼-inch mesh hardware cloth,
boards, or metal flashing. Make all connections flush and secure
to keep mice, rats, and other mammals out. Make sure you don’t
trap an animal inside when you seal off a potential entry (see
“Opossums in or Under Buildings” the handout Evicting
Animals from Buildings for additional information).
Install a
commercially designed and engineered chimney cap (homemade caps
are often unsafe and may be a fire hazard). You can still have
fires in your fireplace; however, the “cap” will keep
opossums and other wildlife out. (For information on how to remove
opossums from chimneys, see “Raccoons in Dumpsters and Down
Chimneys” in the handout on Raccoons.)
Prevent opossums
from accessing rooftops by trimming tree limbs away from structures
and by attaching sheets of metal flashing around corners of buildings
(Fig. 7). Commercial products that prevent climbing are available
from farm supply centers and bird-control supply companies on
the Internet (Fig. 8). Remove vegetation on buildings, such as
English ivy, which provide opossums a way to climb structures
and hide their access point inside.
Opossums
in or Under Buildings |
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| Figure
9. A one-way door can be used in conjunction with
a welded wire or hardware cloth barrier. (Drawing
by Jenifer Rees.) |
Occasionally
an opossum will find a suitable den site in or under a building.
Opossums normally occupy a den site for only two or three consecutive
nights. However, during the mating and nesting season, females
are attracted to warm, dry, dark, easily defended areas, and
will remain longer if the setting remains favorable.
Should
you choose to remove the animals, a wildlife control company
can be hired (call your local Fish
and Wildlife office for a current list of contacts), or
you can complete the process yourself using the steps below.
(For detailed information, see Evicting
Animals from Buildings.)
1. Seal
all openings except the main opossum entrance. Use sturdy
wire mesh (1/4-inch hardware cloth or similar materials)
to screen vents near ground level in houses and other structures.
Tightly
seal holes in foundations or under porches to prevent opossums
from entering.
2.
To determine entry points, you can use "tracking patches"
of a fine layer of sand, talcum powder, or dust placed at
suspected entrances. Wadded up newspaper lightly stuffed
into the entry hole also works great. Opossums will push
the paper out of the way when exiting.
3.
After dark, when the opossum has left seeking food they
will leave tracks at the den entrance. Inspect
the powder or the dislodged newspaper for exiting opossum
tracks.
4.
Once an opossum has left the building, immediately seal
the entrance with a hardware cloth "one-way door"
(Fig. 9). (You will not want to permanently exclude at this
point, not being sure of the number of opossums present.)
The one-way door can be made from 1/2 -inch hardware cloth
that is attached over the opening, and hinged at the top
and left loose on the other 3 sides. It should be larger
than the opening so that it cannot swing inward. The opossum
will push it open to leave, but cannot re-enter.
5.
Put a layer of powder on the inside and outside of the door
after the one-way door has been installed for two to three
nights. Any footprints should be outside the door with none
inside. This means the opossum is out. If you have any doubt,
then smooth out the dirt on both sides of the door with
your hand or a tool, reapply the powder and observe. Once
a couple of days have gone by with no footprints, the opossum
is probably gone. Another way to check is to open the door
and shove a few pieces of wadded up newspaper into the opossum’s
entrance. If the paper stays in place for two to three nights,
then the opossum is gone.
6.
Once you are sure all opossums are out, permanently seal
the opening.
To try
and drive an opossum away, consider harassing the animal.
Lighting up the den site with battery operated flashing lights
and adding a portable radio can cause an opossum to seek a
more suitable habitat. (For detailed information, see Evicting
Animals from Buildings.) |
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Figure
10. An opossum’s dexterous paws make it possible for
it to open various types of fasteners, latches, and containers.
(From Christensen and Larrison, Mammals of the
Pacific Northwest: A Pictorial Introduction.) |
Enclose
poultry (chickens, ducks, and turkeys) in a secure outdoor pen
and house. Opossums will eat poultry and their eggs if they
can get to them. Note: Other killers of poultry include
coyotes, foxes, skunks, raccoons, feral cats, dogs, bobcats, weasels,
hawks, owls, other poultry, and disease.
To prevent
opossums from accessing birds in their night roosts, equip poultry
houses with well-fitted doors and secure locking mechanisms. An
opossum’s dexterous paws make it possible for it to open
various types of fasteners, latches, and containers.
To prevent
opossums from accessing poultry during the day, completely enclose
outdoor pens with 1-inch chicken wire placed over a sturdy wooden
framework. Overlap and securely wire all seams on top to prevent
opossums from forcing their way in by using their weight. To prevent
opossums from reaching in at ground level, surround the bottom
18 inches of the pen with smaller-mesh wire.
See Figures
7 and 8 for examples of how to prevent opossums from climbing
enclosures.
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Figure
11. Install two electrified wires, 6 and 10 inches above
ground and onto existing fence posts, poultry pen supports,
and other structures, using the proper insulators. A single
strand of wire may be sufficient, but two wires will provide
added insurance against the animal making the climb. Run one
or two electrified wires toward the top of the fence to prevent
bobcats and other species from jumping the lower hot wires and
making the climb.
(Drawing by Jenifer Rees.) |
Fence orchards
and vegetable gardens. Opossums can easily climb wood or wire
fences, or bypass them by using overhanging limbs of trees or
shrubs. See Figures 6 and 7 for examples of ways to prevent opossums
from climbing fences and accessing crops at ground level. Wire
fences will need to have a mesh size that is no wider than 3 inches
to keep young opossums out.
Protect
fruit trees, bird feeders, and nest boxes. To prevent opossums
from climbing fruit trees, poles, and other vertical structures,
install a metal or heavy plastic barrier (Fig. 12). Twenty-four-inch
long aluminum or galvanized vent-pipe, available at most hardware
stores, can serve as a premade barrier around a narrow support.
Alternatively,
a funnel-shaped piece of aluminum flashing can be fitted around
the tree or other vertical structure. The outside edge of the
flared metal should be a minimum of 18 inches away from the support.
Cut the material with tin snips and file down any sharp edges.
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| Figure
12a and 12b. A predator guard can be secured around trees,
pipes, posts, and other structures to keep opossums from climbing.
It can be made from a piece of aluminum flashing or sheet metal,
held together with wire, nails, or screws, and painted to blend
in. (Drawing by Jenifer Rees.) |
Regularly
pick up fallen birdseed and fruit to prevent attracting opossums.
Trapping
Opossums
Trapping and
relocating an opossum several miles away seems an appealing method
of resolving a conflict because it is perceived as giving the
animal a second chance in a new home. Unfortunately, in addition
to being illegal (see “Legal Status”),
moving opossums often will not solve the original problem because
other opossums will replace them and cause similar conflicts.
Hence, it is more effective to make the site less attractive to
opossums than it is to routinely trap them.
It is legal
to trap an opossum, and then release the animal at the site of
capture. With this option, the opossum is trapped and released
on site after its reentry into a structure is prevented by physical
exclusion. (See “Opossums in or Under
Buildings” for exclusion techniques.)
In such a
case, the opossum is evicted within its home range and because
it is familiar with its surroundings, it can soon find suitable
food and shelter. In the event young are present but were not
noticed prior to trapping, allow the female back inside to tend
to her dependent offspring.
A downside
to this approach is the possibility that the animal may simply
enter someone else’s attic, chimney, or similar place. Then,
if someone else has to trap the animal, they will be dealing with
a trap-smart opossum, making its capture difficult.
If an opossum
needs to be trapped, use a single- or double-door type live trap
that measures 11 x 11 x 36 inches. Bait with cracked boiled eggs,
sliced apples or other fruit, or vegetables to prevent attracting
cats or small dogs. Place the trap where the animal, or evidence
of the animal has been seen.
Public
Health Concerns
Although opossums
might carry several diseases of significance to humans, their
role in the transmission of any of these diseases is uncertain.
Anyone handling a dead or live opossum should wear rubber gloves,
and wash his or her hands well when finished.
There is
convincing evidence that the parasite that causes Equine Protozoal
Myeloencephalitis (EPM), a disease in horses, is carried by the
opossum. EPM is an infection of the central nervous system; the
neurologic signs that are most apparent in horses include dizziness,
weakness, and spasticity.
While there
are no guaranteed methods of preventing exposure to this parasitic
organism, horse owners can minimize risks by making facilities
less attractive to opossums. Remove or seal up food that opossums
might find attractive, such as cat food left out, grain sitting
in buckets, feed in uncovered bins, and garbage in open cans.
If feed has been left exposed, check it for droppings before serving
it to your horses.
Droppings
need not be fresh to be dangerous; the parasite can live outside
a host and remain potentially infectious for as long as one year.
The rabies
virus does not exist in Washington opossum populations, and for
some unknown reason opossums rarely get rabies elsewhere.
If a person
is bitten or scratched, immediately clean the wound by thoroughly
scrubbing it with soap and water. Flush the wound liberally. A
physician should examine all wounds caused by an opossum.
Legal
Status
The opossum
is unclassified and may be trapped or killed year-round; no permit
is necessary. No permit is necessary for the use of live (cage)
traps; however, a special trapping permit is required for the
use of all traps other than live traps (RCW
77.15.192, 77.15.194;
WAC
232-12-142).
It is unlawful
to release an opossum anywhere within the state, other than on
the property where it was legally trapped, without a permit to
do so (RCW
77.15.250; WAC
232-12-271). Except for bona fide public or private zoological
parks, persons and entities are prohibited from importing opossums
into the state without a permit to do so (WAC
246-100-191).
Because legal
status, trapping restrictions, and other information about opossums
change, contact your local Fish
and Wildlife office for updates.
Additional
Information
Books
Christensen,
James R., and Earl J. Larrison. Mammals of the Pacific Northwest:
A Pictorial Introduction. Moscow, ID: University of Idaho
Press, 1982.
Conover,
Michael. Resolving Human-Wildlife Conflicts: The Science of
Wildlife Damage Management. Boca Raton, FL: Lewis Publishers,
2002.
Hygnstrom,
Scott E., et al. Prevention and Control of Wildlife Damage.
Lincoln, NE: University of Nebraska-Lincoln, Institute of Agriculture
and Natural Resources, 1994. (Available from: University of Nebraska
Cooperative Extension, 202 Natural Resources Hall, Lincoln, NE
68583-0819; phone: 402-472-2188; also see Internet Sites below.)
Ingles, L.
G. Mammals of the Pacific States. Stanford, CA: Stanford
University Press, 1965.
Larrison,
Earl J. Mammals of the Northwest: Washington, Oregon, Idaho,
and British Columbia. Seattle: Seattle Audubon Society, 1976.
Maser, Chris.
Mammals of the Pacific Northwest: From the Coast to the High Cascades.
Corvalis: Oregon State University Press, 1998.
Nagorsen,
David W. Royal British Columbia Museum Handbook: Opossums,
Shrews, and Moles of British Columbia. Vancouver, BC: University
of British Columbia Press, 1996.
Verts, B.
J., and Leslie N. Carraway. Land Mammals of Oregon. Los
Angeles: University of California Press, 1998.
Internet
Resources
Burke
Museum’s Mammals of Washington
Prevention
and Control of Wildlife Damage
The
Internet Center for Wildlife Damage Management
Tomahawk
Live Traps
Wildlife
Control Supplies
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