Science Bloggers for Students DonorsChoose Challenge

Monday, October 27, 2008

Urban Wildlife Watch: Opossums

photo credit: wikipedia

The Virginia Opossum, scientific name Didelphis virginiana, is the only Marsupials of North America. Yes, marsupials like kangaroos and koala bears. Opossums, like their Australian cousins, bear immature young and nurse them in the female's pouch.

Traditionally, opossums live in forested areas near water. Every living thing needs fresh water for survival. But they do quite well in cities, especially in neighborhoods with trash bins and alleys or near dense areas by parks. In fact, they are one of the most common animals in urban and suburban areas. They are often mistaken for rats because of their long noses and naked scaly tails. And many people regard them as vicious and scary, but they are actually quite passive. They hiss and bear their teeth as a threat, but when confronted they usually run or play dead - playin' possum - if you will.

Like rats, opossums will eat most anything. They are omnivores, meaning they eat protein like insects, mice, and moles but also vegetables and fruits, especially persimmon fruits (very common US forest tree). Not being picky eaters, they will dine on free protein of other dead animals - road kill. Hence, they are ecologically important as carrion eaters. As a result, they often become road kill themselves, which is how most people encounter this animal.

In fact, I met this fellow this past weekend on the street in front of my home.

As a mammalogist, road kill is a laboratory specimen and this is a teaching moment. During my training in graduate school, we collected road kill and preserved them for later study. This guy is actually in pretty good shape. Ten years ago I would dressed him (removed all of the fleshy insides), bagged him up and dropped him in a deep freezer until I was ready to prepare a museum flat-mount of him. My mother was not happy with me.

Here's a quick Anatomy lesson.
  • Opossums have thin leathery ears. His ears were actually split. Look closely at the photograph. He probably got snagged earlier in life.
  • They have a thick long prehensile tail which can wrap around limbs and help secure the animal as it climbs trees and fences. When they are babies they can actually hang in trees by their cute.
  • They have padded paws (or hands and feet) with opposable thumbs. Opossums are pretty dexterous or handy and can get into your trash or compost very easily.
  • Those knots in a string are NOT fetuses in the uterus. Opossum babies don't get that big in the mama's belly. I'm pretty sure that is the intestines and those dark lumps are poo. I can't be sure, sorry for that. The scientist in me was tempted to thoroughly examine and dissect this fellow but I didn't have any gloves nearby. Plus, I don't think my photographer was up to the challenge of taking photos of this interesting, yet gross science lab experiment.
  • I'm quite sure this fellow was a male. He was rather large and heavy. he was about the size of a house cat. Females tend to be a little smaller than males. Plus, I didn't notice any dead little ones. Because the young do stay with the mom - in the pouch or on her back - when a female is hit by a car her young often succumb as well.
This picture gives you an idea of big he is. I know it's gross, but stay with me. Something else I noticed a little way from the possum - I tend to drop the O when I say the word.

  • At first I thought the pale white organ was its heart, based on shape, but now I think it is it's cecum. The cecum is the blind pouch in the intestine, the appendix is a cecum and all of the stuff looks like food matter or poo. That dark red organ could be the spleen. Spleen are very dark red and slender organs. Like I said, I wasn't able to poke around and confirm things, but I feel pretty sure about it. But I bent over to take a closer and I noticed parasites.
  • This fellow has a whole mess of round worms coming from what I though was its heart. Do other mammals, beside dogs, get heart worms? I don't know, but it wouldn't be a big surprise. Parasites, internal and external, are apart of life for animals, even urban wildlife. But now that I think it is the cecum, then these could be intestinal worms, which are very common among mammals.
  • And one last interesting fact about opossums - they have an amazingly short life span, usually 1-2.5 years, even in captivity.

I did my civic duty and removed his carcass from the street to prevent any unpleasant meetings by the neighbors or other potential road kill victims who might want to check out the scene.

I put the carcass in my compost bin.


sheila said...

OMG I almost threw up from that post! lol.
OM!!!!!!!!!!! educational, but yuck! lol

DNLee said...

yeah! that's science. it gets gross sometimes. and I love it!

lisaschaos said...

Ew, yes educational, but ew. Most often when I see a possum it's road kill but last winter I got to snap some photos of a live one and my son was snapping photos of one in Missouri and we were amazed at how different they look from each other.

Kam Kam Speaker I am said...

Haha, thats gross Nicole.
In your compost bin! ew.

DNLee said...

Kam: where else should I put him. Next year I'll have a great skeleton..just kidding.

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