Interesting Projects for Home or School

Dung Jars

By Harold Eddleman, Ph.D. President of Indiana Biolab. (indbio@disknet.com)

Some very interesting fungi grow on the dung of horses, cattle, buffalo, deer, rabbits, mice, rats, elephants, giraffes and many other animals which eat plants. Such animals are called herbivores (plant eaters). Do not use the dung of cats and dogs because they eat meat and their dung will develop mostly smelly bacterial populations. However, the dung (droppings, scat, feces) of plant eating animals develops interesting fungi and demonstrates a succession of species. The dung of different plant eaters give rise to strikingly different fungi.

Pilobolus, a very beautiful, tiny, jewel-like fungus develops in a few days on lumps of horse manure. Collect fresh horse droppings; those less than a day old work best and are less likely to contain fly eggs. Place one lump of dung in a jar with a loose fitting cover so that it gets plenty of air. The loose lid holds in moisture, yet admits enough air for the desired aerobic conditions. Fungi must have oxygen. Furthermore, air prevents the growth of anaerobic bacteria which produce the foul odors associated with rotting manure. Actually, this project is going to be free of strong odors if you are careful to avoid getting the dung soaking wet. Fungi require moist conditions for growth. The ball of dung should be in contact with liquid water 2 to 5 millimeters deep. Add water as needed to maintain a dryish surface, but moist inside the dung ball. Room temperature is ideal. If in doubt start several jars and keep them in different locations.

A succession of fungus species will appear. After a day or two, there may be a few stalks of spores of Aspergillus, and other sugar molds. These use proteins and sugars; horse manure contains very little of these and that limits the growth of the sugar molds. You may also see the hyphae (these look like fine hairs; they are tubes filled with protoplasm) of various fungi. After a few days, Pilobolus will appear. This genus sends up sporophores shaped like tiny bowling pins standing bottom up. The little bowling pins are about 2 to 5 mm tall and hyaline (totally water clear) and puffed up tightly with liquid. The distal end (the end away from the dung) will develop a beautiful yellow sporecap which turns black in a day. Then the exciting part begins. Water pressure continues to build inside the stalk until it bursts sending the cap of spores flying upward a few feet striking the nearest light precisely. They always fly toward the light.

Try taping a paper or transparent plastic film firmly over a lamp 2 to 4 feet from the Pilobolus. Caution: Light bulbs can set paper on fire and burn your house down. Have your parent help with this project and check it frequently to be sure the paper is cool. How far can the tiny cannon balls travel, six feet? The rain of tiny cannon balls will make a visible spot on the target.

Here is a better way. Cover the jar with a loose-fitting pane of glass or a piece of plastic. Cut a 1/4 inch hole near the center of a 6-inch square of aluminum foil and tape this foil on top of the glass. Place your light so that the beam of light passes through the hole in the foil and hits the lump of horse manure. After a few days, does the black deposit of spores on the clean glass coincide exactly with the hole in the aluminum foil? You do not have to set up a special light for this project; you can use any existing light such as your study lamp or ceiling light. Just make sure the light which passes through the hole in the foil hits the manure. If the culture dries then water pressure may not develop to fire the tiny cannons!

Sometimes the color (wavelength) of light is important in biological reactions. You can experiment using various colors of cellophane over the hole in the aluminum foil. Use a different jar for each color of light filter. I have never tried using different colors of light. If you try different colors of light, send me an e-mail telling me how it came out. If you try colored light, be careful that you don't fool yourself. You should repeat the experiment a three times and be very careful that all the jars are as close to exactly alike as possible. If some jars are dried out more than others that might cause different results; don't you think? Make a list the things you will try to keep the same:

In nature, Pilobolus fires its spores toward the lighted sky so they land on vegetation and stick to the leaves. When a horse eats the leaves, conditions in the digestive tract activate the spores so they are ready to grow in the dung. Pilobolus is difficult to grow without the assistance of a willling horse. However, I believe I have grown it on sterile rabbit dung.

After a week or two you may not see many changes in your dung jars because the growth that is taking place is deep inside the dung ball. Then tiny toadstools (gill mushrooms) should appear. Coprinus is a typical genus likely to appear. You may observe some less common fungi. Plan to keep your dung jar a couple months or longer to see the gill mushrooms (Basidiospores). If you have a microscope remove a gill of the mushroom or any toadstool outdoors, and exam under a microscope use a drop of water and a coverglass. You should find 4 tiny spores growing at the corners of each club (basidium). The first time you try this experiment, you may give up long before the one or two-inch mushrooms appear. That is because the mushrooms eat really hard to digest materials and the manure will become very decayed in appearance. Finally, when the mycelium has accumulated enough food stores, it will form a button inside the manure and within a day or so, the toadstool will grow upward out of the manure.

Now that you are an expert on the fungi of horse dung, try other types of dung. The dung of mice and insects is so small that you can't place it in water. Instead place one layer of thick filter paper in a petri dish and keep it moist for a few weeks. The fungi that grow will be different than those which grew on horse dung. You don't expect the same fungi because the mouse, rat, insect, rabbit, or elephant ate different food so it will contain different spores. If you don't have filter paper and petri dishes, then use a few layers of paper towel in a jar. Remember to keep the paper moist but not with a puddle of water on the animal dung. For best results dung must be moist but not shiny wet. If the balls of dung are melting down they are too wet. If you find some mouse dung that is many months or years old, try it. Does it give any fungi? Are they different from those on fresh mouse dung?

Don't be too surprised if some insects come from your manure. Remember that many kinds of flies lay their eggs in manure. Beetles and other orders of insects also feed on or grow in manure.

Keep a record of your dung jar on a sheet of paper. It might look like this:

Date         Day       Observations (what I saw); also enter what you did

98 Jan 12    0    I began my dung jar using a "horse apple" fresh from the horse today. I placed it in a pint jar on some paper towel with just enough water to wet the towel. Manure is green-black.

98 Jan 13    1    No fungi. Manure is turning blacker. Towel getting dry; added more water. I put a better cover on the jar--clear polyethylene, but I punched a hole for air to enter.

98 Jan 14    2    There is some mold on the manure. I added more water--towel did not dry out.

I would be delighted to receive an e-mail from you describing how you did this experiment and what happened. All good scientists report their results. I will publish the best reports on my web site. Click here to read the results of other people's dung jars. That page also links to reports on other projects.

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A slight variation of dung jars is to place wood such as a piece of a tree limb in a jar. Try various sizes of wood and kinds of wood (oak, tulip tree, pine, etc). Select a weather beaten tree limb with or without bark and cut to 6 inches long or any convenient length, stand it on end in a quart or larger jar. Add water to a depth of 1/2 to 1 inch and cover with a loose fitting cover. That will provide ideal conditions for fungal growth. It will also be excellent for the growth of any wood boring insect larvae inside the wood or between the bark and wood. Most wood borers are beetles. You are sure to produce some fine fungus specimens. If you start several jars with various types of wood from rotten logs to live branches, you will grow a greater variety of fungi and increase your chances of hatching out some insects. The wood pieces may be any diameter from twig to two inches or more. Let wood jars sit for many months. Wood is difficult to digest and it will take some insects and fungi many months or years to mature. You might want to let some jars go until the wood has completely rotted to "nothing."

Try other kinds of jars. Leaves, humus from a forest floor, garden soil, dead plants, green plants, peat, vegetables. Caution: some of these will develop dusty molds which might grow in your nose or lungs if inhaled. Do not place your jars where infants can reach them. Discard dangerous jars carefully.

Safety Warnings

This experiment carries very limited risk of infection or injury unless you fall out of a tree collecting wood or step on a rusty nail in the horse stable. Horse manure is reputed to contain tetanus spores. Therefore be very careful not to step on rusty nails or pitchforks in horse barns. Wear protective shoes. Tetanus (lockjaw) develops in deep wounds infected with Clostridium tetani. You must go to a doctor immediately if you suffer such an injury. Anyone likely to get such wounds should make sure his tetanus shots are up to date. If you suffer a puncture wound of the above type, it is extremely urgent that you see a doctor right away because lockjaw is extremely serious. Death is the expected outcome. Avoid inhaling mold spores if any develop in this project.

There are safety precautions which you should read and observe. Study safety manuals at your library and ask your teacher and parents to review your research plans. If you can't do an experiment safely, postpone the experiment until you can conduct it safely.

Revised 1999 Sep 17