By Ruth Forsgren
Several winters ago while exploring behind the cabins at
Beaver Creek Reserve I stumbled across some interesting tracks in the snow. The
critter that had left these tracks had five toes on each foot; when I looked at
the track of the front foot, I was transported back to high school and the
coral director screaming “jazz hands people, jazz hands!” (For those of you
that have never performed in a swing choir, jazz hands are when the performer
ends a number and the hands are palm to the audience with the fingers straight
and spread comfortably apart.) The alignment of the critter’s back toes however
looked rather painful. The back foot has four of the toes that point forward,
but the fifth toe looks almost dislocated. If you were to hold your hand up in
front of you, fingers to the sky, then rotate your thumb to point towards the
ground you would have a close approximation of the track left by the back foot
of a Virginia opossum. You see, opossums are one of the few animals that have
an opposable thumb or finger. This means that the thumb is opposite of the
other fingers and allows those fingers to grasp things.
Since the opposable
thumb is on the back foot this makes opossums good at climbing and moving about
in the branches. But the opposable thumb is not the only fascinating trait of
the opossum, let’s look at what else makes these creatures unique and
interesting.
First let’s get the name straight we have opossums
(generally pronounced uh-paa-sum), Virginia opossums to be exact. They are
often simply called possums, but keep in mind that an opossum and a possum are
two different animals. Virginia opossum is one of 100 different species that
are found mostly in the Americas; while possums are a very different marsupial
that live in Australia and New Guinea. The Virginia opossum (Didelphis
virginiana) is the only opossum native to North America, north of Mexico. The
critters are technically a neotropical species or historically of the tropical
regions. Opossums are not equipped to survive extreme cold temperatures, but
that hasn’t stopped these critters from expanding their range from Costa Rica
to southern Ontario Canada. Prior to European immigration and settlement, the
northernmost limit of their range was Kentucky, Ohio, Indiana. But their
tolerance of humans and ability to find shelter among human structures has
allowed their range to expand northwards. They live in a wide range of habitats
but do prefer areas near a water source.
The Virginia opossum is a short-legged, pointy faced, stout
little animal whose body size equates to a large house cat. Their fur is
typically in the gray color range with darker legs and white tipped guard
hairs. The tail, feet and ears are all hairless and susceptible to frostbite in
the colder climates. They are primarily nocturnal (active at night) creatures,
whose sensitive, long whiskers help them feel their way through the night.
Opossums also hold the record for most teeth of any North American mammal, at
50.
The opossum is North America’s only marsupial. A marsupial
is an animal with a pouch where the young are raised. After a gestation of less
than two weeks the female opossum, or jill give birth to underdeveloped babies
referred to as joeys.
The joeys are about the size of honeybees and must crawl
into the mother's fur lined pouch and attach to a teat where they will stay and
continue to grow for up to another 10 weeks. Once big enough to leave the pouch
young opossums can be seen hitching a ride on mom’s back and are on their own
at around five months.
The opossums tail is another feature that makes these
critters unique. While lacking fur to help keep the animal warm their tails are
prehensile, which means that they can grasp and hold things with their
tail.
They can use it to help support
themselves as they move through the branches, but their ability to hang from
their tails and sleep is just another fallacy we picked-up from fairy tales.
While young opossums have been seen hanging from their tails, it can only be
done for a few moments. Their body does not have the muscles that would be required
to make this trick possible.
Opossums do have a great trick to avoid being eaten though.
When threatened by a predator that they cannot run away from the opossum will do
a variety of generally impolite activities such as growl, belch, hiss, pee or
poop to ward off the attack. If these tricks don’t work the opossum might “play
dead”.
Playing dead is an involuntary
reaction, in other words they cannot control when it happens. But when it does
the opossum will stiffen, fall on its side, pull the lips back to expose the
sharp little teeth, foam around the mouth and secrete a foul smelling liquid
from the backend. Since this is an involuntary reaction they cannot control how
long the episode lasts, in young animals it can last up to six hours.
Possibly because of their scruffy, slightly rat-like
appearance, their nocturnal habits and gruff behaviors, opossums are often
treated as unwanted pests. In actuality they should be looked upon as welcome
guests. They are quite intelligent animals, at least when it comes to finding
and remembering where food is. In maze and food placement recall tests they
outscored most other animals including rats, rabbits, cats and dogs. Their
omnivorous diet makes them great members of nature’s clean-up crew, helping to
keep the environment healthy by eating things like: carrion, garden pests
including snails, slugs and beetles and the sources that can attract these
pests, rotting fruits and veggies. They can lower the number of ticks that can
carry Lymes disease in an area, because the opossum is such a fastidious
groomer they remove and eat over 90% of the ticks that they pick up. According
to the National Wildlife Federation a single opossum eats roughly 5000 ticks
per season. Among North American mammals, opossums are one of the lowest risks
for developing and spreading rabies. Their naturally low body temperatures make
it difficult for the rabies virus to replicate. Opossums are also immune to the
venom of all poisonous North American snakes except the coral snake. Opossums produce a peptide that causes the
immunity, researchers are working to replicate that peptide for an inexpensive,
but universal antivenom for snakebites.
So, if you are lucky enough to have these critters living in
your neighborhood don’t contact pest control, consider yourself lucky and leave
them alone to do their thing.
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| Young Opossum at Trempealeau National Wildlife Refuge by Ruth Forsgren |
