Animal Tracks - Opossum (Didelphis virginiana)

Opossums are the only North American marsupials. A marsupial is an animal with a pouch, like a kangaroo.

Opossum trail at Burlington. Photo by Kim A. Cabrera 2002.

Opossums have pointed noses and naked tails. They are the only North American mammals with prehensile (grasping) tails. The tail is used to assist in climbing. It also stores extra fat reserves, enabling the animal to survive lean times.

Opossums have opposable thumbs on their hind feet which help them to grip branches and climb. They are the only non-primates with opposable thumbs.

Opossums have the most teeth of any North American mammal.

In the trail pattern at left, the two tracks, front and hind, overlap each other. Because the tracks are doubled, the trail can look like that of a much larger animal.

Early morning is the best time to find their tracks. The trails in fine, dry soil tend to age quickly, especially along riparian areas. Opossums can be found in many environments, including cities and wilderness. They are opportunistic feeders and can utilize many of the scraps people throw away, thus they are often found raiding pet food dishes and garbage cans.

When baby opossums are born, each one weighs 1/200 of an ounce, is less than ½ inch long, and lacks fully developed hind limbs. Up to 14 young are born after only 12 to 13 days of gestation. Of these 14 young, only about nine survive. The entire litter could fit into a teaspoon. They climb into the mother's pouch, where they remain for about ten weeks. When they are big enough, they ride around on their mother's back.

Baby opossum.

Opossum trail in sand near the Eel River. December 2000.

When attacked, an opossum can play dead, or "play possum." When using this defensive strategy, they drool and emit an unpleasant smell which discourages predators. They also climb to escape danger. When threatened, they will hiss and show their 50 sharp teeth.

They nest in abandoned burrows or fallen trees. Opossums eat a variety of foods and are able to adapt to many different environments, from cities to wilderness.

Their tracks show five toes on the front foot and five toes on the rear, including the opposable thumb. The thumb lacks a claw.

On the left is the trail pattern of an opossum in river sand. The tracks nearly overlap each other in the alternating pattern that is typical of a walking opossum. The opposable thumb is very prominent in some of these tracks.


Personal Notes on Opossums
I recently walked outside at night and happened to see a very small animal by the woodpile. Upon closer examination, I determined that it was a baby opossum. I watched on the following nights and was treated to the sight of three baby opossums making their first forays out into the world. Their little ears were pink and looked too large for their heads. They moved slowly and tried out their climbing skills in a nearby tree. Fascinating animals to watch. When I used to live in the city, opossums would come around at night and get into the garbage cans. They used overhead powerlines as a sort of aerial highway. Pretty smart.

The left pair of tracks. Front track is ahead of the hind track. Note the opposable thumb in the hind track.	The right pair of opossum tracks. Quarter gives scale.

	This plaster cast of the hind foot of an opossum shows details that normally don't show up in field casts. The structure of the opposable thumb is easy to see here.
This young opossum visited me one night when I left some snacks outside. Here he is devouring some tasty morsel.
	Another young visitor. These young opossums were probably 8 or 10 weeks old. Photos taken in summer 2000.
Still another of my opossum visitors. Photo taken near Redway, California.
	This opossum got into the kitchen and was hiding behind the stove. It left on its own when I left the door open for it.

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Opossum tracks in sand. Front foot at top and right hind foot on the bottom. The hind print partially covers the front one.	Opossum trail pattern diagram.


Two left hind opossum tracks. These footprints show the opposable thumb that makes this animal unique in North America.
	A pair of left tracks. The hind track overlaps that of the front foot.