Imagine a world without decay…
A world where autumn leaves don’t decompose, but pile up, year by year and layer by layer, until they cover the forest floor. Soon all kinds of grasses, shrubs, and other low-lying vegetation would be buried beneath the fallen foliage. In no time at all, the leaves would smother the trees themselves. The fields, too, would be covered by a blanket of dead insects and weeds, from which no seed could sprout. Such a world would soon be completely uninhabitable, its life-cycle brief and self-defeating.
Thank goodness for the saprotrophs, Mother Nature’s cleaning crew. They get their scientific name from the Latin words sapro, meaning “rot or decay”, and troph, meaning “nutrition”. They’re also known as detritivores, or “waste eaters”.
This diverse group of creatures is anything but glamorous – bacteria, fungi, termites, slugs, earthworms, maggots, and flies are just a few – but they are an indispensable part of every ecosystem. These are the agents of rot, mold, and decay, and it’s their job to recycle dead organic matter, breaking it down again into the fundamental components of life.
Carbon, oxygen, hydrogen, and nitrogen account for 96 percent of all organic molecules, with sulfur and phosphorous also playing an essential role. Living cells take these basic elements and combine them into more complex substances, like proteins, carbohydrates, and nucleic acids (like DNA, for instance). Whenever any organism dies, decomposers go to work immediately, breaking those complex molecules back down into simpler forms – which will then be reused by other living things.
Think of it like a vast, planetary recycling program, which takes the raw material of life and repurposes it. After all, with trillions of living things on planet Earth, all competing for these key nutrients, we can’t afford to have anything go to waste!
Take those autumn leaves, for example. Instead of piling up endlessly, they are quickly dissolved and consumed by different species of fungi, or mushrooms.
The mushrooms we see when walking through the woods are only the fruiting bodies (read as “reproductive organs”) of the fungus – and that’s just the tip of the iceberg. The rest of the fungus lies underground, unseen, in sprawling web-like networks called mycelium. These underground webs are formed of thin white filaments called hyphae, which grow right up through the ground, penetrating the carpet of fallen leaves and dead plant matter. The hyphae then secrete acidic enzymes, which dissolve and break down the vegetation, enabling them to absorb the nutrients they need to grow and reproduce.
Mycelium networks can reach gigantic proportions. The biggest yet discovered is a species of honey fungus (Armallaria solipides) found in the Blue Mountains of Oregon. The fungus is believed to cover approximately 3.7 square miles (2400 acres), and could be more than 8,000 years old!
Certain species of fungi are the only decomposers capable of breaking down wood. Compared to most forms of plant life, trees are extremely resistant to rot and decay. This is due not just to their size, but also to their chemical composition – specifically, the presence of lignin, the complex, carbon-based polymer which gives wood its toughness and rigidity.
When the first trees appeared millions of years ago, there were no detritivores able to break down the lignin contained in their wood and bark. So the vast forested regions of that era were buried where they fell, creating most of the coal beds and fossil fuel deposits that we use today. Near the end of the Coniferous Period (around 300 million years ago), a new player appeared on the scene: white rot fungus. Possessing enzymes that dissolve lignin into usable nutrients, the white rot fungus was able to break down those prehistoric trees, slowing down fossil fuel formation drastically.
There are many other species, besides fungi, involved in plant decomposition: millipedes, woodlice (like the common “rolly-polly” or pill bug), and invertebrates like worms, snails, and slugs. These little fellows feast on all kinds of vegetable matter; dead roots, leaves, grasses, and so on. They even eat dirt! Their digestive systems break down organic matter, concentrating the minerals and nutrients, then excreting the perfect fertilizer for the next generation of plant life.
How do we Get Rid of All Those Bodies?
Of course, plants aren’t the only thing that need to be decomposed. Death comes to animals of all shapes and sizes, as well. And when it does, a whole host of colorful detritivores are waiting to consume and clean up the remains; primarily bacteria, insects, and their larvae.
Animal decomposition begins the moment the heart stops beating. Living cells use oxygen for fuel, and create carbon dioxide as a waste product. Without constant circulation, there is no fresh supply of oxygen, and no flushing of carbon dioxide waste. The pH balance drops quickly. The cells and tissues become unstable, and are soon dissolved and broken down by their own enzymes. This process is called autolysis.
Next comes putrefaction, the breakdown of the body by anaerobic microbes and bacteria. These invisible swarms proliferate in the absence of oxygen, consuming the body’s proteins, lipids, and carbohydrates, and breaking them down into methane, ammonia, hydrogen sulfide, and other chemical byproducts. The buildup of these chemicals causes the bloating and discoloration of the corpse, as well as the infamous, gut-wrenching odor.
Carrion insects are the next to arrive, especially flesh flies (Sarcophagidae) and blow flies (Calliphoridae). These tiny scavengers lay their eggs in every available orifice of the corpse, usually the nose, mouth, and any open wound. After hatching, the insect larvae (maggots) use the decaying soft tissues as a food source, burrowing under the skin and feasting on the rotten flesh.
There are also several species of carrion beetles (Silphidae, Nicrophorinae, and Dermestidae), which feast on the flesh and skin of animal corpses. Their longer life-cycle makes them of interest to forensic entomologists, who can use them to help determine time of death in criminal investigations. Some species are even kept in colonies by natural history museums, where they are used to strip every last bit of flesh from skeletons.
Eventually, the activity of the maggots and the buildup of noxious gases becomes too much. The skin ruptures, the corpse bursts open, and foul smelling fluids come spilling out onto the ground, pooling up around the body. This gives the insects and their larvae more access, and exposes the remains to the open air, where aerobic bacteria and microbes can contribute to the decomposition process. Together these voracious eaters will strip a corpse down to cartilage and bones – and even these will be carried off and eaten by larger scavengers, as a valuable source of calcium.
Hey, nothing goes to waste, remember?
The liquefied remains of the animal’s organs and tissues are eventually soaked up by the soil. The carbon, nitrogen, phosphorous, and other essential elements thus return to the earth, where they will nourish new plant growth. This in turn will feed other herbivores, which will become food for predators, and so on. Sooner or later, they all become food for the saprotrophs – the cleaning crew, the unsung heroes of the animal kingdom.
Man’s Place in the Cycle
And so, the great circle of life continues. Death and decay are a necessary part of that circle, just as essential as birth and growth. Each makes the other possible. Like yin and yang, they form a delicate balance, an intricate dance. On the one hand, countless species of plants and animals take the basic ingredients of life and build them into increasingly diverse and complex forms. On the other, bacteria, fungi, and detritus insects tear them down again, dissolving them back into simpler molecules – only to begin the process all over again.
Thanks to these humble servants and their unseen, unceasing, and unappreciated labor, nature enjoys a perfect, closed-loop recycling program.
Well, nearly perfect.
Since the industrial revolution, at least, humans have been a bit of a wild card in the game, introducing large amounts of waste and pollutants into the natural environment. Most organic matter – like food waste, cardboard and paper products – is broken down and recycled in a matter of months, by the same organisms responsible for decomposition in nature.
Untreated wood decays similarly to the process described above, with some species (like white oak or cedar) being much more rot-resistant than others. However, much of the lumber we use is pressure treated with chemicals to make them more resistant to rot, insects and even fires. It can take 20 years or more for the chemicals to “leach out” of the wood, and regular decomposition to begin.
We also produce large quantities of inorganic matter, which is not so easily disposed of. One of the most common examples is the metal used for tools, wires, structural frames, and countless other applications.
Ashes to Ashes, Iron to Rust
The breakdown of metal is called corrosion, and it’s actually a kind of chemical reaction. The most common form of corrosion by far is that of iron alloys. Metals containing iron (like steel, which is an alloy made from iron and carbon) react with water and oxygen in the air, and the atoms of the iron actually lose some of their electrons to the oxygen atoms through a process called oxidation. Oxidation results in an entirely new compound, iron oxide – the flaky, reddish brown substance we know as rust.
But iron is not the only metal that corrodes. The discoloration, or tarnish, that develops on silver, copper, or brass is a form of corrosion. Gold and platinum are exceptions. These noble metals are highly resistant to corrosion, and will not noticeably tarnish or break down under normal conditions.
Aluminum is also extremely durable, but for a different reason. Aluminum reacts almost instantly with oxygen in the air, forming a microscopic coating of aluminum oxide. This coating, invisible to the naked eye, then protects the rest of the aluminum from further corrosion. This is called passivation.
Nickel and chromium also share this quality, and are both used to make other metals more corrosion resistant, either by combining them into a more durable alloy (like stainless steel) or by applying a thin coat of chrome or nickel over another substance (commonly called plating). Metals treated in this way can resist corrosion almost indefinitely. Just think of your stainless steel sink, which never rusts despite constant exposure to water.
But however fast or slow, almost all metals eventually succumb to corrosion, which actually changes their chemical makeup from that of a pure element or alloy to that of an oxide, sulfide, or other derivative – which is the form in which they are often found as ores in the ground.
Decay Can’t Touch This
Petroleum-based materials (like plastic and Styrofoam) are more problematic. Most plastics are immune to decay from bacteria and fungi, and can only be broken down by sunlight through a process called photodegradation. Specifically, the ultraviolet rays of sunlight interact with plastic polymers at a molecular level, weakening the bonds that hold it together, making it more brittle and eventually causing it to fall apart into tiny pieces.
However, most of the plastic materials we produce end up buried in landfills somewhere, and are not exposed to much light at all – meaning that it degrades veeerrry slowly, if at all. Styrofoam resists even the effects of light, and could take millions of years to decompose!
Another common, and very durable man-made substance is glass. Although it does flake and crack over time (a process called “crizzling”) and break into ever smaller pieces, glass does not decay, degrade, or chemically decompose. The most common type is made of silica (silicon dioxide), a strong, stable, and abundant mineral found in sand and quartz crystals. The Corning Museum of Glass has a specimen on display that is more than 4,000 years old.
There are also samples of a type of glass called moldavite, which was formed by the intense heat of a meteor impact 14 million years ago! Many such samples are still intact today, indicating that glass can indeed be preserved over centuries and even eons.
As you can see, many man-made products and materials have a tendency to linger, impacting natural ecosystems in ways that we still don’t fully understand. But one good thing about Mother Nature is that she evolves. She is always adapting and developing new ways to cope with and correct imbalances in the environment; like the fungi that learned to feed on trees all those millions of years ago. Who knows what she will come up with next?
One thing we do know is this: The more we learn about decay, and the organisms and processes behind it, the more we can live in harmony with the process, and the great circle of life of which we are a part.