Fungus Firearms

Every day on the cow pastures of the world, salvos are shot from
dunghills. Few people have heard of these cannonball volleys, however, because
they take place on such a miniature scale. The life cycle of the Pilobolus
fungus shows how our Creator can display beautiful design even when disposing
of manure.

When you think of cannonballs, the first thing that pops into your mind probably
isn’t a tiny black speck the shape of a deflated ball. Yet more of these tiny
projectiles are fired each day than all manmade cannonballs ever fired in military
history.

Why do so few people know about these special little cannonballs? Easy. Because
to see them you have to stick your face a few inches away from a fresh cow patty.

Several species of “hat-throwing fungus” in the genus Pilobolus live
on the fresh dung of cattle, horses, deer, and other grass-eaters. Like all
fungi, they are decomposers that consume dead or decaying matter. They start
as spores, which grow into thin threads (called hyphae), feeding on the nutrient-rich
manure. When the time comes to release new spores, specialized stalks, called
sporangiophores, sprout and grow to a height of a centimeter or less. On top
of these stalks appear the cannonballs, called sporangia, which contain the
new spores.

Light-seeking Fiber Optics

This particular fungus has beautiful sporangiophores, which are transparent
and shine like spun glass. How ironic that such jewels thrive in filthy surroundings.
A bulge just below the cannonball-like sporangium is not just beautiful but
serves as the cannon barrel.

To fire properly, the stalk must point toward the sun and fill with water.
God designed the bulge to refract the sun’s rays into the base of the swelling,
where certain pigments absorb the light. This happens in the morning when the
sun is low on the horizon.

To ensure that the sporangium is shot to greener pastures, it needs to have
a trajectory away from the home patty. Sporangia shot straight up in the air
wouldn’t get far—the farther they’re shot, the better. So shooting toward a
morning sun is the best strategy.

If the sporangiophore is not aimed directly at the sun, the light rays hitting
the pigments unevenly will cause one side to grow more than the other until
the sporangiophore is aimed right at the sun.

At the same time the bulge’s fluid (cytoplasm), which is very high in certain
ions, causes water to flow into the bulge (by osmosis), increasing the fluid
pressure to bursting levels.

Ready, Aim, Fire!

Once the sporangiophore is aimed at the sun, the water influx causes this bulging
balloon to burst. The little black sporangium, mounted on top, is shot from
its glistening perch with an initial velocity of about 45 mph (72 km/h). It
speeds away in an arc and can land over 6 feet (2 m) away.

Not bad, considering the sporangium is less than one tenth of a millimeter
wide. If it is lucky, the sporangium lands on a blade of grass a reasonable
distance from its stinky source.

Why does it need these incredible ballistics? Because cattle find their own
dung repugnant and won’t eat adjacent grass, Pilobolus needs to shoot
its sporangia a good distance from the home patty. Landing on grass several
feet away increases the chance of being eaten by another cow.

Most other fungi release their spores to the four winds. In so doing, only
a tiny fraction of a fraction of their spores actually land on a suitable surface
to grow. Also, most fungal spores of other related fungi are sprinkled out of
the sporangium like pepper from a shaker.

Unlike these other fungi, for the Pilobolus to have successful offspring
its sporangium needs to be eaten, processed through the gut of an herbivore,
and deposited in a fresh pile of dung. So Pilobolus spores are kept
inside a special protective sporangium, which is designed for successful sharp-shooting
and surviving the hazardous journey sloshing about in digestive juices in a
cow’s gut.

It Works!

If the tiny sporangium lands on a blade of grass several feet from the launch
patty, a cow or some other herbivore may eventually come along and chomp off
a mouthful of grass. The spores remain protected within the sporangium throughout
the entire digestive tract. After the cow patty is deposited, the spores grow
out of the sporangium, and the cycle begins anew.

Unwelcome Hitchhikers

Although Pilobolus sporangia are not harmful to cattle, often nasty
stowaway parasites, called lungworms, take advantage of Pilobolus’s
projectiles. Lungworm larvae, which are deposited in the same dung as the fungus,
need to be eaten by an herbivore. They squirm up the stalk of the sporangiophore
and crawl onto the sporangium. By this insidious method they can enter another
grazing host.

Once ingested, they take a circuitous route to the lungs, where they become
adults. Here the adults breed and often cause serious respiratory illnesses
in a variety of livestock. Their offspring are coughed up and then swallowed
into the digestive tract, where they again wind up in dung.

Pilobolus is an innocent accomplice. Left alone, it is a good little
fungus. The creative hand of God has not only made Pilobolus an effective
decomposer of dung but has also bestowed on it ballistic abilities to blast
its offspring to a better place to continue its life cycle. Imagine how, in
a perfect world before the Curse, this fungus went about its job recycling refuse
without harm to anything.

Answers Magazine

April – June 2010

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Answers in Genesis is an apologetics ministry, dedicated to helping Christians defend their faith and proclaim the gospel of Jesus Christ effectively. We focus on providing answers to questions about the Bible—particularly the book of Genesis—regarding key issues such as creation, evolution, science, and the age of the earth.