Feeding on the Dead

To scavengers and decomposers, the stench of rot is as appealing as fresh-baked cookies are to you. That foul fragrance comes from bacteria springing into action. All living things are teeming with bacteria. Normally, these microscopic passengers dine on the contents of an animal’s intestines or gobble up oils and flakes of skin.

But after an animal dies, the bacteria go to work on the animal itself. This results in stinky chemical emissions that let scavengers know a meal is nearby. After the scavengers have their fill, insects, bacteria, fungi, and other tiny creatures finish the job.

A rotting carcass smells stinky to us. But to scavengers and decomposers, it smells as tasty as fresh-baked cookies do to you! The stench comes from bacteria. All living things are covered with these tiny life forms. Normally, bacteria eat the contents of an animal’s intestines or oils and flakes of skin.

But after an animal dies, the bacteria start eating the carcass. This releases stinky chemicals that tell scavengers a meal is nearby. After the scavengers have their fill, they leave. Insects, bacteria, fungi, and other tiny creatures finish the job.

Bacteria also lurk in the dirt. There are hundreds of thousands of microbes in a single teaspoon of soil, waiting to decompose dead leaves, trees, and other plant matter. Some of these bacteria hang out in the stomachs of other creatures, called detritivores. Termites, for example, feast on dead trees and plants. “You think of them as eating the wood, but they’re feeding the bacteria inside their gut and poop out the decomposed material,”  says Blanchard.

All decomposers are part of the carbon cycle, which feeds every living thing—including humans. When plants and animals die, decomposers reduce them to the elements and chemicals that they were made of. The most important of these elements is carbon. “Carbon is the building block of all life,” says Diva Amon. She’s a marine biologist and a fellow at the Natural History Museum, London. “It’s what ultimately everything comes back to.”

Bacteria also lurk in the dirt. A single teaspoon of soil contains hundreds of thousands of microbes. They’re waiting to decompose dead leaves and other plant matter. Some of these bacteria even live in the stomachs of other creatures, like termites. Termites chew on dead trees and plants. But they’re not actually eating the wood, says Blanchard. “They’re feeding the bacteria inside their gut, and they and poop out the decomposed material,” says Blanchard.

Decomposers play an important role on Earth. When plants and animals die, decomposers break them back down into the elements they were made of. The most important of these is the element carbon. “Carbon is the building block of all life,” says Diva Amon. She’s a marine biologist at the Natural History Museum, London. Every living thing—including humans—needs carbon to live. Decomposers return carbon to the environment so it can be used again.  

Decomposers don’t just feast on dead animals. They also help break down poop! Creatures like dung beetles help keep piles of poop from covering farmlands. They roll up dung into balls and bury their snack in the soil. It’ll either become a future meal or a place to lay eggs. Most animal poop includes undigested morsels as well as dead bacteria, salts, and other animal waste. Dung beetle larvae eat the solid waste, while adults drink the liquid part.

If it doesn’t become a meal, poop takes about a year to fully decompose. And animals—including humans—poop a lot, from a few ounces to hundreds of pounds per day. The same bacteria and fungi that break down dead animals and plants also go to work reclaiming the carbon and nitrogen in waste. That’s why manure, which is made up of animal waste, is such a powerful fertilizer. When it decomposes, its chemicals return to the soil, ready to feed new plants.

Decomposers don’t eat just dead animals. They also help break down poop! Creatures like dung beetles help keep piles of poop from covering farmlands. They collect dung and roll it into balls. Then they bury the ball in the soil. Either the beetle or its offspring will eat it later. Most animal poop includes some food the animal didn’t digest. There are also dead bacteria, salts, and other animal waste. Dung beetle larvae eat the solid waste. Adults drink the liquid part.

If a decomposer doesn’t eat it, poop takes about a year to fully break down. And animals— including humans—poop a lot. Depending on the species, it can be a few ounces or hundreds of pounds per day! The same bacteria and fungi that decompose dead animals and plants also break down waste. They return the elements carbon and nitrogen to the soil. That’s why animal manure makes good fertilizer. As it decomposes, its chemicals return to the soil, ready to feed new plants.

All things decompose, but how long it takes varies. A small animal like a mouse can go from fresh corpse to carbon in about three weeks, while it can take a century for a whale fall to fully decompose.

Different conditions like temperature, moisture level, and pressure can speed up or slow down decay. “The deep ocean is so special because it’s extremely cold, with temperatures just above freezing,” says Amon. Because of the chill, “decomposition is much, much slower in the deep sea.”

Meanwhile, on land, “water and warmer temperatures makes decay faster,” says Blanchard. The bacteria and fungi that drive decomposition need water and oxygen to get to work. That’s why you can find amazingly well-preserved creatures encased in freezing ice or trapped in oxygen-less tar pits—the decomposers that would normally break them down can’t survive in those harsh conditions.

Regardless of how long it takes them, decomposers help ensure that our world isn’t overrun by death and decay. “If nothing fed on dead animals,” says Amon, “there’d be carcasses everywhere.”

All things decompose eventually. But how long it takes can vary. A small animal like a mouse can break down in about three weeks. Meanwhile, it can take a century for a whale fall to fully decompose.

Different conditions can speed up or slow down decomposition. Temperature, moisture, and pressure all have an effect. “The deep ocean is so special because it’s extremely cold, with temperatures just above freezing,” says Amon. Because of this, “decomposition is much, much slower in the deep sea.”

On land, it’s warmer, so things usually decay faster. But the bacteria and fungi that drive decomposition need water and oxygen to get to work. They can’t survive in harsh conditions like freezing ice or oxygen-less tar pits. That’s why amazingly well-preserved animals are sometimes found in those spots.

Regardless of how long it takes them, decomposers have an important job. They help make sure that our world isn’t overrun by death and decay. “If nothing fed on dead animals,” says Amon, “there’d be carcasses everywhere.”