Didelphis virginiana Kerr, 1792

Virginia opossum

North America's only marsupial, 50 teeth and a talent for theatrics.

Order: Didelphimorphia
Family: Didelphidae
Group: Wildlife
Ontario status: Native, expanding northward

Why it matters

Garbage and pet-food raiding, denning under structures; eats ticks and slugs, so ecologically useful; rarely a rabies concern.

Origin

Native to eastern North America; expanding northward into Ontario as winters warm.

Behavior

Nocturnal, solitary, slow-moving; the famous 'playing dead' is an involuntary stress response, not a trick; hisses and drools when cornered.

Living conditions

Dens in brush piles, under decks, in attics and garages; needs cover and water; poor cold tolerance sets its northern range limit.

Signs of presence

Tracks: hind foot shows an opposable 'thumb'
Overturned compost and raided pet food
Hissing from under the deck at night
Leaf nests in sheltered voids

Weaknesses

Poor cold tolerance, Ontario winters are the range limit
Thanatosis makes it easy to approach and confirm
Slow and clumsy, easily excluded by intact structures

Myths and facts

Myth Opossums are rabies-ridden vermin.
Reality Opossums are remarkably rabies-resistant, their lower body temperature makes them poor hosts. They are among the least likely wild mammals to carry rabies.

Research notes

Morphology

Body 33-55 cm, naked prehensile tail 25-40 cm; weight 2-6 kg. Grizzled gray-white fur, pointed snout, 50 teeth, more than any other North American land mammal.

Diagnostics

Naked prehensile tail + opposable hind thumb + 50 teeth; unmistakable in Ontario.

Easily confused with

Raccoon (Procyon lotor) Raccoon has a furred ringed tail and masked face; the opossum's tail is naked and rat-like with a pointed snout.
Muskrat (Ondatra zibethicus) Muskrat is semi-aquatic with a laterally flattened tail; opossum is terrestrial with a round prehensile tail.

Life cycle

Egg: N/A, marsupial mammal
Nymph or larva: Pouch young about 2 months, back-riding about 1 month
Adult: Sexual maturity about 1 year; lifespan 2-4 years wild
Egg to adult: Gestation about 13 days + pouch development about 2 months
Generations per year: 1-2 litters per year

Development

Marsupial: about 13-day gestation; neonates crawl to the pouch, emerge at about 2 months, then ride on the mother's back.

Reproduction

Up to 20+ neonates born, but only about 13 teats, typical surviving litter 7-9 × 1-2 litters/year.

Distribution

Native range: Eastern and central North America
Ontario: Native, expanding northward with milder winters
Global: Not established outside North America

Ecology

Omnivorous scavenger; poor thermoregulation, frostbitten ears and tails common at the range edge; small home range; high predation turnover.

Resistance

Unknown, not applicable.

IPM implications

Exclusion and attractant removal (pet food, compost); range-edge biology means winter itself limits populations. Licensed wildlife-control rules apply (Fish and Wildlife Conservation Act).

Chemical ecology

Anal-gland musk released when threatened (mild beside a skunk); thanatosis is accompanied by drooling and a foul anal secretion that sells the 'corpse' performance.

Genetics and DNA

Reference genome published: chromosome-length assembly (DNA Zoo dv-2k, 2n=22).

Taxonomy

Order Didelphimorphia, family Didelphidae. Didelphis virginiana Kerr, 1792, North America's only marsupial.

Open questions

Rate of northward range expansion in Ontario and its interaction with urban heat islands.

References

Animal Diversity Web, Didelphis virginiana species account (University of Michigan)
McManus (1974), Didelphis virginiana, Mammalian Species