Chapter 14

SLIMEBALLS SAVE THE WORLD

Okay, remember those slimeballs? The ones with lancet flukes in them? It turns out that they do more than just infect cows, snails, and ants. They help save the world.

Well, okay, not the whole world. But they do make sure that the corner of the world where ants and cows and snails live doesn't come crashing down. Here's how it works:

When cows are looking for something to eat, they stay away from grass that's really green. Green grass is good for them, but it's green because of the cow pies fertilizing it. Now, these cow pies don't cause problems in themselves - cows are smart enough not to eat them. But cow pies have lancet flukes in them. Thus, there are fluke-infected snails nearby, which means that there must be flukey ants sitting atop stalks of green grass, waiting to be eaten.

So cows have evolved to avoid bright green grass. They don't want to get infected with lancet flukes, after all.

But a problem arises when there are too many cows and not enough grass to go around. The cows wind up eating the green grass, and getting lancet flukes in their stomachs. Less grass to go around, more sick cows. And, it turns out, sick cows have fewer calves. The cow population drops, and there's more grass for everyone.

Get the picture? The parasites control the population. They're part of nature's balance.

So what happens if you get rid of the parasites? Bad things.

Not long ago, some cattle ranchers decided to increase their herds with parasite-killing medicine. They doped every cow until all the parasites were gone. So their cattle had more and more calves, and they ate all the grass, green or not. More hamburgers for everyone!

For a while.

It turned out that those little clusters of bright green, parasite-laden grass were important. They were holding down the topsoil. Without parasites to keep the cows in check, every square inch of grass got eaten, and soon the grassland turned into a desert. New plants came in, desert shrubs that made it impossible for grass to return.

All the cows died. All the snails died. Even the ants got blown away.

Without our parasites to keep us in check, we're all in trouble.