Why Don't We See More Dead Animal Remains While Strolling in the Woods?

Have you ever noticed that when you’re hiking or just taking a walk in the woods, you rarely see a dead animal? There are plenty of animals out there, and like everyone else, they die. So why don’t we ever stumble upon their bodies? Is there some kind of secret forest clean-up crew that scrubs the evidence before we get there? Well, yes, there is.

Jennifer DeBruyn is an environmental microbiologist who studies decomposition and biodegradation, and is super cheerful for someone who spends her days looking closely at rotting corpses. DeBruyn says the fact that we don’t see dead animals, even though animals are dying all the time, highlights the difference between how decomposition works for animals versus plants.

Unlike plants, which can take a while to break down, animals decompose very quickly. That’s because animal bodies are high in moisture and high in nutrients, DeBruyn says. Animals have a high ratio of nitrogen, phosphorus, and other nutrients relative to carbon. 

“The ratio of carbon to nutrients in an animal body is much closer to what microbes and decomposers need, so they've got food in the right amounts, which means they can work really, really quickly to decompose animals.”

Read More: Animals Respond to Death in Many Ways. Mourning Might Be One of Them.

So, where do all those death-eating microbes come from? Most of them come from inside the animal itself. 

“Animals have this massive load of microbes inside their bodies,” says DeBruyn. And those are the first ones to the buffet when an animal dies. They start decomposing the animal from the inside out, she explains.

These same microbes do a lot of good while the animal is alive, but that’s in part because they’re kept in check by the immune system, which keeps them from getting out of hand or into parts of the body where they would be harmful. But after death, there’s no more immune system to patrol the microbes.

Now that the body’s cells aren’t getting oxygen anymore, the cells go through autolysis, a process in which cells are destroyed by their own enzymes. 

“This means all the cells are liquefying and turning into a bunch of macromolecules, carbohydrates, proteins, and fats,” says DeBruyn. “These macromolecules are just really delicious food for those microbes, food the microbes aren’t getting from digestion because the animal isn’t eating.” This whole process begins very quickly after death, and goes even faster in warm weather.

Not all the creatures that feast on the dead are microscopic. Insects show up for the free food, too. Flies find a dead body very quickly and lay their eggs in a natural orifice, such as an eye, or in a wound. Then the eggs hatch into larvae, also known as maggots, that feed on the dead body, adding still more digestive enzymes. 

“They really can churn through a lot of tissue extremely quickly,” says DeBruyn.

Bigger scavengers show up for the feast, too. Vultures are most familiar. But many animals that aren’t obligate scavengers, such as raccoons and rodents, scavenge when their usual food source is in short supply, often in winter, says DeBruyn.

Emily Studd is a wildlife ecologist who studies vertebrate scavengers, mostly ravens and wolverines, at Thompson Rivers University in British Columbia. Studd says scavengers can show up within hours in warm weather, though in winter, she has seen carcasses that froze and were covered in snow, which lasted until the snow melted, at which time the scavengers moved in quickly.

The speed at which scavengers arrive and complete their work depends in part on the number of scavengers in an area. In very biodiverse habitats, such as rainforests, it might take only a few minutes for them to find a dead animal, says Studd.

We don’t often see the scavenging process, either. Scavengers tend to carry off a carcass, or parts of one, to eat in a place where they feel safer, says DeBruyn. The body parts tend to get scattered around, so they’re not so obvious to someone hiking by on a trail.

Though they spare us the sight of dead animals, the role of scavengers and microbes that feast on the dead is not to keep the landscape clean and tidy. 

“The role of scavengers is to take the energy that's left in a carcass and transfer it into energy that could be used either by themselves or by the ecosystem,” says Studd. “They’re really a necessary part of the ecosystem.” Microbes, too, recycle nutrients, returning them to the soil, keeping ecosystems diverse and healthy.

So, yeah, all this might be a little gross, but like many gross things, it’s important.

Read More: Apex Scavengers Are Declining – And That’s A Public Health Problem

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article.

• Nature Microbiology. A conserved interdomain microbial network underpins cadaver decomposition despite environmental variables

Avery Hurt is a freelance science journalist. In addition to writing for Discover, she writes regularly for a variety of outlets, both print and online, including National Geographic, Science News Explores, Medscape, and WebMD. She’s the author of Bullet With Your Name on It: What You Will Probably Die From and What You Can Do About It, Clerisy Press 2007, as well as several books for young readers. Avery got her start in journalism while attending university, writing for the school newspaper and editing the student non-fiction magazine. Though she writes about all areas of science, she is particularly interested in neuroscience, the science of consciousness, and AI–interests she developed while earning a degree in philosophy.