A Little Bit More
Most of us have seen the shots of an African savannah with an assortment of hungry animals circling a dead Wildebeest or Zebra. We’re fascinated with how different animals feed on a dead animal and how the carcass quickly disappears. Lions, Hyenas, Wild Dogs, vultures and others converge on a “kill” to get their own share of the food. But in North America, most of us can tramp through woods and field for years without seeing much of anything approaching this activity.
Animals are dying and being killed and eaten all the time in North America – we just don’t see much evidence of it in most instances. But, if we do, it can be quite interesting to watch the process over time as an organism returns, quite literally, to the environment. You won’t see large numbers of large animals feeding on a carcass in North America, but there are certainly many different small, even microscopic, organisms reducing a carcass to the earth.
Temperature is important for decomposition to take place so it follows that during harsh winter weather, little if any decomposition takes place (kind of like having meat in your freezer). But as things warm up, various processes can begin to take place. Once death occurs, and it’s warm enough, tissues in the body begin to break down due to internal enzymes and bacterial action. If the body is available to other animals, insects, especially flies, are an important agent of decomposition as their young, called maggots, feed on the decaying flesh. Larger animals such as coyotes, dogs, foxes, crows, and mice also feed on the flesh and can quickly reduce a carcass to little more than bones, skin and hair/feathers. Although the bones and hair and feathers are much more resistant to decomposition, they too will eventually break down into their chemical elements and return to the soil.
Decomposition may not be a topic we’d like to dwell on often but it is an important, actually essential, part of life on earth. It can be said quite accurately that we are made from the “dust of the earth” – and to the earth we’ll return.
Activities
Decomposition
Objectives: See how decomposition proceeds
Materials: Chicken leg and thigh or small, dead animal, plastic bag, digital camera, and wire “cage”
This may not be a “hands-on” exercise for the squeamish but even they will find this fascinating to watch as it progresses. If you can pull this exercise off, you’ll have shown your students something that is happening all around them, every day – it’s well worth doing.
- Buy a leg and thigh (articulated (connected) if possible) from your local grocery, place in a plastic bag, and keep refrigerated until ready to use. You could use an actual whole, dead animal – mouse, squirrel, or rabbit – but this will add to the “yuck” factor. You decide, although a whole animal may heighten the interest level.
- Decide on a good place on your school grounds or near your home that is out-of-the-way but will permit easy access for your students.
- Once you have your meat, be sure to keep it in the refrigerator/freezer until you’re ready to begin this exercise because you want the meat to be as “fresh” as possible for the start of this exercise.
- Remove the meat from the plastic bag and place the meat at your pre-selected location. Place a wire cage over the meat that will allow small insects and creepy crawlies in, but keep larger animals from taking your subject away. Be sure your cage is secured to the ground so it isn’t easily pushed aside.
- Assign one or more of your students to take a digital photo of the meat on a daily basis.
- Every day, have the student (if you rotate students, be sure that everyone photographs the subject in exactly the same way each time) remove the cage and take a photo of the subject. Over the next 10 days to 2 weeks (this may take longer depending on variables) you should obtain a series of photographs that clearly shows how the subject is decomposing.
- Depending on your equipment, once the series is finished, you may even want to print out your photographs and post them so everyone can see the series quickly and easily.
- Have students take a close look at the each photograph to see if they can determine what factors may be working to decompose the meat – insects, other creepy-crawlies, fungi, nibblings of some animal.
- If you find that the time frame you’ve chosen isn’t long enough, simply extend the time you keep an eye on the process until you do feel it is finished to your satisfaction.
Keep in mind that if the weather is on the warm side, the decomposition of your subject will be speeded along but if on the cool side, the opposite will be true.
Key Concepts
Life Cycles, Food Webs /Food Pyramids
Questions
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