This angry baby 'possum from last year's baby season is the background on my laptop.

Generally speaking, opossums have a pretty bad reputation.  Most people seem to think of them only as pests that get into their garbage cans and give birth under their porches.  They can come across as downright vicious, hissing and snapping when they feel threatened.  Their black eyes are lined with dark fur that stands out vividly against the pale fur of their pointed faces, heightening their impression of ferocity.  Although they will sometimes “play ’possum” when cornered, they can also put up quite a fight, as anyone whose dog or cat has ever picked a fight with one likely knows.  They’re not the most intelligent of animals, and the results of their lack of intelligence are evident in their high roadkill body count.  In fact, opossums have the smallest brain size relative to body size of any mammal—and, coincidentally, more teeth than any other North American mammal.  So that can make for a fun combination.

Still, I have to say, I love opossums.  They’re just awesome.  For one thing, they’re marsupials, meaning their young are born very early in development and then spend several weeks in a pouch in the mother’s abdomen as they continue growing.  The Virginia opossum is the only marsupial in North America, having made its gradual way north over the last several millennia from the rainforests of South America, where its relatives still live.  The American marsupials are descended from some common ancestor with Australian mammals in the distant past when Australia and South America were connected as part of the same supercontinent.

Opossums also have prehensile tails, like some monkeys, which they use to gather leaves and other nesting material and to hold onto tree limbs for balance.  They have grasping front and back feet with almost-opposable thumbs.  When you go into more detail in opossum anatomy, you find even more fascinating peculiarities.  For example, its genus name, Didelphis, which literally means “double-wombed” in Latin, describes its unusual bifurcated reproductive system.

The opossum explores her new cage.

People visiting TreeHouse often wonder why we accept opossums, and they ask us “What good are they?”  After swallowing the urge to launch into a diatribe about how I don’t think humans have the right or the knowledge to make judgment calls about which animals are “good” and which are “bad”, I generally respond that opossums are omnivorous scavengers, and like any scavenger they fill an important niche in the ecosystem.  Opossums really will eat just about anything, and that is very important for keeping an ecosystem clean and healthy.  Imagine what the world would smell like if it weren’t for scavengers like vultures and opossums speeding up the process of dead organisms returning their nutrients to the environment.

We admit a lot of orphaned baby opossums at TreeHouse.  Typically, the mother was killed by a car, and one or more of the babies in her pouch survived.  Opossum baby season has not arrived yet, but when it does I will have to devote a post to them—they’re ridiculously adorable.

At the moment, we have two adult opossums living at TreeHouse.  Both came in last summer as orphans, and for different reasons these two were unable to be released.  The first was much too habituated to humans to be released.  The people who found her after her mother was killed by a dog intended to release her when she was old enough, but unfortunately she became too tame.  Luckily, though, she is an absolute sweetheart, so we are able to hold her during education programs and we can let her out of her cage for exercise.

After dunking her head in water and then rubbing it on a log, the fat opossum looked like she had painted her face for camouflage.

The other opossum is just fat.  She was going to be released last fall, but on the day we went to pack up her and her litter-mates from the release training cage, we found her on the floor of the cage with a large wound on her back.  So, we had to keep her over the winter while the wound healed.  It did heal, but opossums are somewhat prone to obesity.  They store fat in their tails and also, somewhat disgustingly, in deposits at the corners of their eyes.  Despite all our efforts to control her diet, the opossum gained a great deal of weight.  As a result, she moves very slowly and can’t really climb, so unless she gets in shape we won’t be able to release her.

The opossum rubs the side of her head on the log to mark it with her scent. She also kept licking it.

The two opossums spent the winter in cages in the mammal ward, so today I was very excited to move them both into deck cages where they have space to explore and climb around.  It’s always a lot of fun watching an animal explore a new environment (with the annoying exception of the bobcat, as I discussed earlier) and today I spent a good hour watching the two of them.  The fat one was the funniest—immediately after arriving in the new cage, she went to the water bowl and dunked her whole head in it.  She then proceeded to rub her head and neck over every inch of the log we gave her to practice climbing, marking it with her scent.  This resulted in the fur of her face being dyed a dark greenish-brown, as if she was trying to camouflage herself.

Based on the amount of time she spent exploring the cage, I now have hopes—not high hopes, certainly, but hopes—that she might lose enough weight to be able to return to the wild.  Unfortunately, opossums, whether in the wild or captivity, have extremely short lifespans.  They very rarely live past two or three years.  Their survival strategy as a species is based instead on their extraordinarily high reproductive rate—a single female opossum has the potential to have raised as many as 26 young after one year of life.  So, although our opossum may may never be able to have a life in the wild, she seems pretty content at TreeHouse, and she is definitely enjoying her new cage!

Exploration's done for the day. Time for a snack.

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