A caller recently asked if I might write something about possums. She has found that a number of her associates and clients are rather offended by them, and are prone to destroy them. What is their real nature, and what should be done when they are found in your area?

I have to admit, I have mixed emotions about possums. I started a band with friends in college named Ergo Possum, based on a rather eclectic Steinberg cartoon in the New Yorker. We got into the whole mystique of possums, and very little of their natural history. I also had a place on a creek in Berkeley where possums would routinely climb up the roof and crawl along our loft window, causing more than a little concern to my girlfriend who would mutter "giant rat," or some such endearing phrase. My sister had chickens she thought were being eaten by them.

I've found them in backyards around the country, and had never really given them their due consideration. Possums, or opossums, as they are called in the Americas, are actually quite interesting animals, and could use the public relations assistance.

Opossums are older than flowering plants and lived side by side with the dinosaurs, perhaps as far back as 130 million years ago. The American Opossum, Didelphis marsupialis, is a widely distributed mammal in Americas and is found now throughout most of the Eastern and Pacific region of the US. It appears to have been one of the small number of successful invaders from South America when that continent connected to North America ages ago. More recently, humans probably introduced it to the western U.S., where it quickly naturalized.

Opossums are not related to rats or other rodents. They belong to the marsupial family, like the kangaroo and koala of Australia. This refers to its marsupium or pouch. Its young are born in an undeveloped state at about 13 days, and then must make a heroic journey up to the pouch. They are born blind, without ears or hair, and are about 1/2 inch long. They are assisted by the mother who must remain upright to orient them, and will clean out her pouch and may smooth down the hair to the pouch with her tongue, a gesture confused sometimes with actually placing them inside. Once in, they must find one of 13 nipples, which they will remain attached to for the next two months while they complete much of their development. At about two months they may begin to venture out of the pouch and will ride on the mother's back until they are weaned at 3 to 3 1/2 months.

Opossums are prolific, and need to be. Of as many as 20 young born, typically only 5 to 8 live until they are weaned. While they may live up to ten years in captivity, an opossum rarely survives more than a year in the wild. They are slow, and while they have 50 teeth and can feign aggressiveness, they are actually very docile and can easily be captured and eaten or killed. When very frightened they tend to go into a shocklike state, or "play dead", which can either protect them or make them even more susceptible to predation.

They really are among the best animals to have roaming our backyards at night. Aside from their docile behavior, they are omnivores and scavengers, so they tend to remove rotting fruit and dead animals, and eat garden snails, insects, rats, and snakes. (They may even be immune to rattlesnake venom.) Like many other wild animals they are also opportunists, so it always a good idea to put pet food away and secure garbage.

They seem to be more resistant than any other wild animal to disease, including rabies. Therefore, they tend not to pass along diseases. This is good reason to leave them to their work. Other animals will quickly fill a niche left by an opossum that is killed or displaced, and these will more likely carry disease that can be passed on to humans and pets. Like most wild animals, they make poor pets, even though opossums are tested to be as bright as dogs and have thumbs on their toes and a tail that is useful for climbing and carrying things.

Despite their large rat-like appearance and the fact that they prowl the darkness looking for food, as so much of nature that we may fear, opossums actually help us out quite a bit and are worth having around.