Managing Opossum Problems

The opossum (Didelphis virginiana) is a house cat sized mammal (4 -14 Ibs.) with moderately long fur that ranges in color from white to dark gray. The fur is frequently darker on the legs and lighter on the back. Its face is long and pointed with dark, rounded, paper-thin, hairless ears. Opossums have 50 teeth, more than any other North American mammal. The tail is hairless, scaly and prehensile. They have five toes on each foot and the inside toe on the hind foot is opposable. Opossums have expanded their range to include all of California.

Biology

Opossums are the only marsupials (pouched mammals) in North America. They breed from January through November and produce two litters per year. The undeveloped young are born 13 days after mating. They crawl to the female pouch (marsupium) and attach themselves to one of the 7-13 teats. Development continues in the pouch for 7 - 8 weeks. Young opossums will stay with the female until they are weaned at about 4 months of age. Except for females with young, opossums are solitary animals.

Opossums are omnivores and eat a wide variety of foods including fruits, vegetables, nuts, meat, eggs, insects, carrion, pet food, and garbage. They are found in many different habitats from woodlands to highly developed residential areas. In urban areas, they have been found living in attics, garages, chimneys, woodpiles, under houses or decks, or in any place that offers protection. Although they are very common in urban areas, opossums are not often seen due to their nocturnal habits.

Damage

Opossums become a nuisance when they move into urban areas. When they live in or near inhabited buildings, the animal's smelly nesting habits and discharge of anal fluids cause offensive odors. Opossums can damage buildings by pushing in screened vents or window screens, scattering insulation, and chewing electrical wiring. They frequently get into garbage and may injure pets or expose them to disease in disputes over pet food. Opossums prey on wild birds and are capable of eliminating local populations of some species.

Disease

Opossums are carriers of many diseases: tuberculosis, relapsing fever, herpes virus, tularemia, salmonella, spotted fever, toxoplasmosis, coccidiosis, trichomoniasis, Chagas Disease, yellow fever, and rabies (rarely). They are important reservoirs for leptospirosis (hemorrhagic jaundice) in wildlife and humans. Leptospirosis is transmitted through the urine and feces of infected animals. Humans frequently pick up the disease by eating unwashed produce or windfall fruit, or by putting unwashed hands to their mouth (gum, cigarettes, etc.). Opossums are also heavily infested with fleas, ticks, mites and lice which are known carriers and transmitters of disease.

Problem Prevention

Opossums are attracted to urban areas by the easy accessibility of food, water, and shelter. Reducing or eliminating the availability of all of these factors will keep opossums from moving in or encourage them to leave. Tight fitting lids should be kept on garbage cans; pets should be fed during daylight hours and any leftovers removed immediately, water bowls should be emptied or taken in at night; gardens should be frequently harvested and windfall fruit picked up. Food should never be intentionally left out for wild mammals.

Opossums can be excluded from buildings by covering foundation vents with slotted metal vent covers and by using 1/4 inch grid screening to cover attic vents and chimneys. Opossums have been known to enter homes through pet doors. Keep pet doors locked at night. Opossums sometimes take up residence under low decks. They may be excluded by using 1/4 inch grid screening or solid metal flashing. Trench around the perimeter of the deck a minimum of 12 inches deep, insert screening in trench and backfill. Attach top of screening to facade of deck with nails or fence post staples. Before completing final seal on the last entry point, it is wise to make sure no animals are trapped inside. On the night before completing repairs, sprinkle flour in the entrance hole and check for tracks the following morning. If no tracks are evident for 3 consecutive nights, no animals are likely to be present. You may wish to make a temporary one-way exit using 1/4 inch screening. Form the screening into a cone or funnel shape. The large end should be sized to encircle the entry hole and be attached to the facade of the deck or building with nails or fence post staples. The small end should face away from the house and be 4 inches in diameter.

Opossums can be kept away from roof areas by trimming tree branches 10 feet from roof and by keeping climbing plants trimmed away from eave areas.

Direct Control

Opossums may be trapped with a 10x12x32 inch cage trap or they may be shot in rural areas. In urban areas, live trapping with baited cage traps is the best method of control. Since opossums and skunks occupy the same habitat types, open grid cage traps should be covered (top, bottom and sides) with heavy cardboard or 1/4 inch plywood. Almost any type of food can be used as bait to trap opossums. Using fruit, berries, raw egg, or peanut butter rather than meat will reduce the chance of catching neighborhood cats. Place trap in areas of greatest activity or near entry holes.

There are no Federally registered pesticides for the control of opossums.

Laws and Regulations

Opossums are not native to California. They are not threatened or endangered, nor are they classified as game animals or furbearers. It is a violation of California state law for any wildlife to be kept as pets. Only authorized wildlife rehabilitators may keep injured or orphaned wildlife, and then only for limited periods of time. California Fish and Game Regulations prohibit the relocation of opossums and other wildlife without written permission of the Department. For further information on the legal status of opossums and other wildlife, contact your California Department of Fish and Game Regional Office.

For further information or assistance in solving opossum problems, contact your local agricultural commissioner.