Opossums

Figure 1: Photo Credit - Kim Chandler

Overview

The Virginia opossum (Didelphis virginianus, Fig. 1) is North America's only marsupial, a primitive mammal that bears its young only partially developed. When baby opossums are born, they are so small that twenty can be held in a teaspoon. The babies must crawl into an external pouch on the mother's abdomen, where they will feed and continue to grow for the next two months.

Opossums measure two to three 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.

Opossums have many unique features. They have a prehensile tail, which means the animal can use its tail to grasp; for example, it can grab a tree limb and hang upside down. Opossums have digits on their hind feet that act like opposable thumbs. They have 50 teeth, more than any other mammal. They are immune to snake venom.

When extremely frightened, an opossum will go into a catatonic state from which it cannot be aroused. It opens its mouth, curls back its lips, and secretes a foul-smelling substance from its anal gland to simulate the smell of death. The term "playing possum" comes from this ability to "play dead" when confronted by a predator. Often a predator will walk away from the opossum instead of trying to consume it.

Opossums are relative new comers to Maine. Prior to European settlement of North America, they lived only in Central America and the southeastern United States. During the 1900s, the population expanded northward into New England. Most opossums in Maine live in the southern part of the state. Cold temperatures block their northward expansion. Opossums do not hibernate and they are prone to frost bite on tails, ears and digits.

Opossums, like kangaroos, bear live young but must nurture them in an abdominal pouch until the babies are large enough to exist on their own. Opossums are sometimes called living fossils because they are extremely primitive. Opossums can "play dead," drool as if they were sick, or bar their teeth in the face of predators.

Facts About Maine's Opossums

Food and Feeding Behavior

  • Opossums are omnivores and eat a variety of plant and animal matter. Foods include carrion (dead animals), insects, fruits, nuts, grains, slugs, snails, snakes, frogs, and small mammals such as mice. Around human habitation, opossums also eat garbage, pet food, birdseed, poultry, and handouts.
  • Opossums primarily feed by scavenging, eating many road-killed animals including other opossums. In the process, they often become road kill themselves.
  • Because opossums are slow-moving animals, food must be abundant and within a small area. Droughts or extended cold periods that reduce the availability of food can have devastating effects on the population.
  • Opossums accumulate little body fat for winter and do not store food, so they must forage year-round.
  • If opossums are removed from a property and the owners do not remove the food that was attracting the opossum, other animals (e.g., raccoons, skunks, rats) will often take their place.

Den Sites

  • Opossums will den nearly anywhere that is dry, sheltered and safe, including burrows dug by other mammals, rock crevices, hollow stumps, logs and trees, woodpiles and spaces in or under buildings.
  • Opossum fur provides little insulation, so an animal carries dried leaves, grass and other soft material to the den in its coiled tail to line the nest and insulate it.
  • 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.

Reproduction

Figure 2: Drawing Credit Christensen and Larrison

  • Opossums usually have two litters a year of eight to 10 young. Litter sizes of up to 17 young have been reported.
  • The breeding season begins in late January and may continue through July.
  • Being marsupials, opossums give birth to undeveloped young. Only 12 to 13 days following breeding, five to 10 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 young are the size of a house mouse. They leave the pouch for brief periods, returning to suckle.
  • At 80 to 90 days, 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 three and a half months, the young begin to leave the den to feed on their own, and soon disperse to establish their own territories.

Young opossums ride on their mother's back with their feet and tail firmly attached to her fur. (Fig. 2)

Mortality and Longevity

  • Opossums have a high mortality rate at all ages; it is estimated that only 10 percent of weaned opossums survive more than one year. Dogs, coyotes, foxes, raccoons, bobcats, eagles, hawks and owls prey on them, especially the young.
  • Mortality factors include predation, disease, exposure, starvation, and human related mortality (car strikes and shooting). Car kills account for many opossum deaths.
  • Opossums seldom carry rabies. Feral dogs are eight times more likely to carry rabies than opossums.
  • The oldest know wild opossums are two and a half to three years old.

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Viewing Opossums

Opossums are nocturnal, spending the day in dens or other protected spots. They can sometimes be seen during daylight hours, however, however, especially in winter when food is scarce. (They do not hibernate) At night, opossums forage in areas near their current den, but can travel up to two miles in search of food.

Opossums are solitary animals, and except during breeding season or when a female is with her young, they are rarely seen together.

Although they can climb and are good swimmers, opossums prefer to amble about on the ground. With a top speed of about seven 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 trash cans, 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.

Trails

Opossums readily use trails near streams, ravines and wetlands that are made by humans or other wildlife. Like raccoons and foxes, opossums use culverts as a safe way to cross under roads.

In developed areas, their trails follow buildings and fences. You can find wear marks and hairs where opossums are entering a building or crawling under a fence. Opossum hair is long and silver to gray in color.

Figure 3b: Drawing Credit Kim A. Cabrera

Figure 3a: Drawing Credit Kim A. Cabrera

Tracks

Tracks can be found in mud, snow, or fine soil as well as on deck railings, downpours and climbable surfaces that opossums use to gain access to structures. The opossum's opposable hind digit creates a unique print, pointing as much as 90 degrees from the direction of travel. (Fig. 3)

The opossum's front tracks are about two inches in diameter and hind tracks are slightly larger. The opossum's long tail often leaves drag marks in snow or mud. (Fig. 3)

Figure 4: Photo Credit Acorn Naturalists

Droppings

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. Firm droppings are pointed on the ends and one to three inches long. (Fig. 4)

Droppings can occasionally be seen along trails and near favorite feeding spots.

Opossum droppings may resemble the droppings of house cats and small domestic dogs, coyotes, and foxes. (Fig. 4)

Calls

Opossums are among the quietest animals that live in Maine, but when frightened or threatened they growl and hiss.

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Preventing Conflicts

Opossums will bare their teeth, growl, and hiss when threatened. They are, however, generally not aggressive and seldom cause problems for homeowners. They sometimes raid trash cans or pet food containers, but these situations usually can be easily remedied by storing these items inside the home or garage. In urban areas, opossums are beneficial as insect, rodent and carrion eaters.

As long as they are kept out of human dwellings, opossums should not pose a problem to homeowners. 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 and help it move outside. Do not corner an opossum, thereby forcing it to defend itself.

Note: If the opossum appears sick or injured, call a wildlife rehabilitator or your regional wildlife office.

An opossum's hunt 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 in the following ways so you do not attract these animals.

Refrain from feeding opossums. Feeding may create an undesirable situation for your family, neighbors, pets and the opossums themselves. These animals often lose their fear of humans and may become aggressive when they do not receive food 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 animals or have them removed.

Secure your 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 daily well before dark.

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 compost in a secure container. Do not put food of any kind in an open compost pile; instead, use a securely covered compost structure or a commercially available opossum-proof composter to prevent attracting opossums and getting exposed to their droppings. (Or, feed compost to worms in a covered worm box)

Figure 5: Drawing Credit Jenifer Rees

Figure 6: Drawing Credit Jenifer Rees

Note: Clean up your barbecue area. Clean the grill and grease trap thoroughly following each use.

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 quarter-inch mesh hardware cloth, boards or metal flashing. Make all connections flush and secure to exclude mice, rats and other mammals. Make sure you don't trap an animal inside when you seal off a potential entry.

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.

Prevent opossums from accessing rooftops by trimming tree limbs away from structures and by attaching sheets of metal flashing around corners of buildings. (Fig. 5) Commercial products that prevent climbing are available from farm supply centers and bird-control supply companies on the Internet. (Fig. 6)

Eliminate access to rooftops by installing sheets of aluminum flashing, at least three feet square, around the corners of buildings. (Fig. 5)

Commercially available metal or plastic spikes can help keep opossums off of buildings. (Fig. 6)

Opossums in or under buildings

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. During the mating and nesting season, however, females will remain longer if they find a warm, dry, dark, easily defended area. To make the area unattractive, consider lighting up the den site with battery operated flashing lights and/or a adding a portable radio. These actions can prompt the animal to seek a more suitable den. Should you choose to remove the animal, a wildlife control company can be hired (call your regional Fish and Wildlife office for a current list of contacts), or you can continue using the steps below.

Figure 7: Drawing Credit- Jenifer Rees

Figure 8: Drawing Credit Christensen and Larrison

Figure 9: Drawing Credit Jenifer Rees

A one-way door can be used in conjunction with a welded wire or hardware cloth barrier. (Fig. 7)

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. Coyotes, foxes, skunks, raccoons, feral cats, dogs, bobcats, weasels, hawks, owls, and other poultry also kill poultry.) 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. (Fig. 8)

To prevent opossums from accessing poultry during the day, completely enclose outdoor pens with one-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 9 and 10 for examples of how to prevent opossums from climbing enclosures)

Its opposable thumb allows an opossum to manipulate fasteners, latches and containers. (Fig. 8)

Fence orchards and vegetable gardens. Opossums can easily climb wood or wire fences, or bypass them by using overhanging limbs of trees or shrubs. Wire fences will need to have a mesh size that is no wider than three inches to keep out young opossums.

Using the proper insulators, install two electrified wires, six and 10 inches above ground and onto existing fence posts, poultry pen supports, and other structures. 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. (Fig. 9)

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. 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, make a funnel-shaped piece of aluminum flashing and fit it 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.

Regularly pick up fallen birdseed and fruit to prevent attracting opossums.

Figure 10a: Drawing Credit Jenifer Rees

Figure 10b: Drawing Credit Jenifer Rees

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. (Fig 10a and 10b)

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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.

Equine Protozoal Myeloencephalitis

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.

Although 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 outdoor cat food, buckets of grain, feed stored in uncovered bins, and garbage placed in cans without covers. 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.

If someone is bitten or scratched

For an as yet unknown reason, opossums rarely get rabies, but if someone is bitten or scratched, immediately clean the wound by thoroughly scrubbing it with soap and water. Flush the wound liberally and then get a physician to examine it.

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Legal Status

The opossum is a game animal; to hunt it, you must have a license and hunt when the season is open. If an opossum is causing damage or is a nuisance, consult Maine's laws on this subject: http://www.mainelegislature.org/legis/statutes/12/title12ch921sec0.html


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Additional Information

Books

New England Wildlife, Habitat, Natural History, and Distribution
Written by: Richard DeGraff, and Mariko Yamasaki
University Press of New England, 2001.
(Available from: www.upne.com)

Resolving Human-Wildlife Conflicts: The Science of Wildlife Damage Management
Written by: Michael Conover
Lewis Publishers, 2002.

Prevention and Control of Wildlife Damage
Written by: Scott E. Hygnstrom, et al.
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.)

Internet Resources

Adapted from: "Living with Wildlife in the Pacific Northwest"
(see Washington Department of Fish and Wildlife)

Written by: Russell Link, Wildlife Biologist, Email Russell Link, with assistance from WDFW Biologists Rich Beausoleil and Rocky Spencer

Design and layout: Peggy Ushakoff, ITT2

Illustrations: As credited

Copyright 2005 by the Washington Department of Fish and Wildlife


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