by Margot F. McMillen
illustrated by David Besenger

Millions of micro-organisms and other tiny life forms supply the world with the right amount of...

Rot.  Decay.  We humans dislike it; some are even afraid of it. "Don't touch that!" we say when we find something rotten. "It's stinky." When we hear the "r" word, we something icky in the kitchen trash.

But there are tiny critters-arthropods, beetles, bacteria, maggots, mites, molds, fungi, and more-that love rot. It's their bread and butter. Their meat and potatoes. Their home.

Let's journey to a forest.

Twenty inches underground, seven young shrews begin to forage for insects, worms and roots. Exploring a tunnel dug by a mouse, one shrew finds a treasure-a snail. She drags it deep into the family burrow to eat later.

Thirty feet above ground, in a tree hollow lined with soft leaves, a flying squirrel family is sleeping after a night of hunting. One squirrel wakes up and pushes the empty nutshells out of the hole.

High above the squirrels, an eagle steps off a sycamore branch and glides over the river. When a shad surfaces, the eagle swoops down and locks its claws around it-Air Express Delivery back to feed its young.

Lots of animals, like squirrels and birds, are easy to see. But all around them are life forms too tiny to notice. In this world, species exist on leftover energy the others throw away or don't use. These recyclers break down the discarded nutshells, dead leaves, fish bones and squirrel manure.

Rot can be beautiful. Tiny animals ate most of this ground cherry (Physalis) seed pod leaving a delicate filagree of veins. Dipped in gold it would make an interesting pendant.

Luckily, these organisms are numerous. Jan Weaver, a scientist at the University of Missouri, counted 40,000 arthropods in three square meters of leaf litter. She says that the critters represented 547 different species, each with its own characteristics, perfectly adapted for its life's work.

To these tiny creatures-nature's decomposers-the ribs on a leaf are like the tallest mountains, and a drop of water is as big as an ocean. Take, for example, the world on a dead branch that falls from the squirrels' tree onto the forest floor. Almost as soon as it falls, a team of termites arrive to eat holes through the dead wood.

It would seem, then, that termites make rot, but nature is much more complicated. Termites do eat wood, but for the real work of rot, you can thank the bacteria that live inside the termites. Those bacteria are so tiny we'd need a powerful microscope to see them, but they can digest an entire tree-as long as the termites are there like taxi cabs to carry the bacteria around.

The real work of rotting things is done by the smallest creatures. These creatures, or micro-organisms, dissolve the old materials. And, believe it or not, they are picky eaters. One species attacks dead bark, another the wood. Many are so specialized that one scientist found seven kinds of mites munching on different parts of the same feather.

Without those tiny creatures, nothing would ever break down and the organic matter trapped in worn-out things could never be used again. Old stuff would pile up-leaves, bones, egg shells, feathers, manure. The forest would be a mess, and new plants wouldn't grow. The forest survives because there is a crumbly foundation of rot.

There's no need to be afraid of these strange species because most are harmless to humans. In fact, before they find their perfect habitat, the micro-organisms are dormant. They drift in air currents and water. When they land on exactly the kind of food they need, their work begins.

Given the right food, temperature and moisture, fungi reproduce quickly. Some forms divide hundreds of times in a single week. The process is so quiet, and the organisms so tiny, that we can't see or hear the work going on. But if we look, we can see the results.

For example, as termites and bacteria do their work, the fallen tree limb grows soft. A cluster of mushroom spores drifts onto the wood and eventually it sprouts with mushrooms. Mushrooms grow quickly, from almost nothing to several inches in one night. Their tiny roots penetrate and widen little cracks in the wood.

When the mushrooms die, new bacteria move into the root tunnels and, soon, earthworms wiggle in from below. An earthworm may be small, but it is wrapped in pure muscle. Its movement opens the termite tunnels further. A hungry mouse follows, chewing through the wood to feast on the worm.

In a very short time, thanks to the action of the termites, bacteria, fungi, earthworms, mice and a host of other creatures, the log has decomposed. Now there's a new layer of crumbly, black rot on the forest floor.

The rot supports plants. A plant seed can't get a hold in a fresh log, but if the same seed drops on soft rot it sprouts. Roots grow into the rot to absorb moisture and organic matter. Ferns pop up, and violets, and a bush from a blackberry seed. The process of building begins again.

Some scientists spend their lives studying plants and animals. They can describe some species in detail and have learned the lifestyles and habits of about 1.4 million more. But the world of rot is still mysterious. There are probably 1.4 million times 10 species still undiscovered.

We live on a lively planet, and it is easy to overlook the critters that make rot happen. But their recycling efforts release nutrients from dead tissue for new generations. From life to rot and back again? The invisible world of decay, you might say, makes the rest of the world go around.

Margot McMillen writes frequently for Outside In.

The rot cycle:

Energy comes to earth from the sun. Some organisms can capture solar energy. These are nature's producers, or builders-green plants that take sunshine, water, carbon and other elements and grow.

Other life forms-animals-use energy stored by the plants. Some animals survive by eating green leaves, while others eat fruits or seeds. Other animals are hunters and prey on smaller ones.

Still other species live on the leftovers. When they break down wastes, they free the basic elements. From arthropods to fungi, these species are the masters of rot. When they have done their work, the basic elements are again available for plants to use. The cycle begins again.