Bacteria and bugs will save us from the zombie apocalypse
The zombie apocalypse is upon us. Hordes of the undead shamble through the streets, hunting for food. But there’s no need for the living to barricade themselves within homes, offices and shopping malls. It’s just Halloween. The zombie hordes that clog the streets are after candy, not brains. And the chainsaw-wielding zombie fighter and that heroine bearing a sword are just fellow trick-or-treaters. But if there really were zombies coming for our brains, we wouldn’t need chainsaws or swords to save us. Microbes, maggots and time are far better weapons.
After a person dies, explains Kimberlee Moran, their body isn’t going to get up and start shuffling out the door. Moran would know. She’s a forensic archeologist — someone who studies human remains to find out about the past. She works at Rutgers University in Camden, N.J. “The idea that zombies can move at all is just completely wrong,” she says. “They’re not going anywhere.”
A dead body doesn’t have anything to drive it, Moran says. “The brain controls the movement of the body through the electrical impulses from the brain through the nervous system.” When a person dies, those electrical impulses disappear, and any potential shambling of the undead disappears with them.
Even if a mad scientist or evil alien virus managed to get those electrical impulses going again, Moran notes, moving would be tough. “The first thing to hamper the shuffling would be rigor mortis,” she says. When a person dies, their cells don’t immediately die. Many of the processes that take place within them keep going. But since breathing has stopped, these cells are no longer getting any oxygen.
That oxygen is needed to charge a cell’s batteries. Muscle cells (and all the cells in the body) rely on a molecule called adenosine triphosphate, or ATP. They use that ATP when they contract and relax. That energy loss transforms ATP into adenosine diphosphate, or ADP. Then, with the help of oxygen, a chemical process loads up the ADP with energy, transforming it back into ATP that can be used again.
Without oxygen, that recycling process stops. But cells are not left with uncharged ADP batteries. Anaerobic activity — energy production without oxygen — turns on to keep the cells going for a little while
Anaerobic activity has a big downside, though. It produces a product called lactic acid, Moran says. That can be used for a short time to turn ADP to ATP again. “It’s enough to cause muscles to contract but not enough for them to relax again,” she says. “Without the ADP-ATP recycling, the muscles stay contracted.” The body locks up “into a giant cramp.” Rigor mortis begins between three and six hours after death, and it will definitely keep a zombie off the streets.
A broken-down body
Long before rigor mortis sets in, the body has started to break down, Moran notes. Cells contain enzymes that can digest cells. When cells are alive, they carefully store those enzymes in pockets away from the rest of the cell, where they process waste. But after death, those enzymes are released and begin to chew through their former homes, a process called autolysis. “The cell breaks open and goo comes out,” Moran says. “Everything soft and squishy eventually liquifies.” That includes muscles and organs — leaving very little for a zombie to shamble with.
Those enzymes aren’t the only things going rogue. The bacteria in a person’s guts keep on eating. And without food coming down the gullet, they’ll chew through the gut and whatever else is in their way. “You have a relationship with the bacteria that live in your gut where there’s no oxygen,” Moran explains. “But when you die, no food is coming in. The bacteria get restless and start digesting the host.”
That process is called putrefaction, and it produces the strong, stomach-turning odors we associate with death. “No one talks about how bad [a zombie] smells,” Moran says. “You should be able to smell it coming!”
People won’t be the only ones to smell the dead. Help flies in, drawn by the scent. “The blowflies are there first,” explains Nancy Miorelli. “They have sensitive antennae and can smell a body from between 10 and 12 miles [16 and 19 kilometers] away. They show up within minutes.” Miorelli is a science communicator and entomologist — someone who studies insects — in Quito, Ecuador.
Blowflies don’t have a taste for human flesh. But their babies do. Blowflies and other fly species lay eggs on the corpse. Those eggs hatch into maggots, eager to slurp up the liquifying body. “The super goopy stage at the beginning usually has maggots,” Miorelli explains. “It’s all fly [maggots] because flies have a liquid diet.”
The maggots slurp up what the cells and bacteria leave behind. “That leaves your hair, tendons, skin, bones — the tough stuff,” Miorelli says. That tougher material may stick around for longer, but even it eventually gets broken down, too. Beetles arrive to lend a hand — or rather, a mouth. “They have chewing mouth parts, and they can chew and break down the stuff the flies couldn’t do,” she says.
“In perfect conditions,” and without bugs, Moran says, “a body will become skeletonized in one to two years.” But location matters. Warm environments can speed up the process. A lot. “In the Amazon, it’s one to two months.”
Add a few bugs, and, Miorelli says, you can go from months to mere weeks. That doesn’t leave a lot of time for zombie shambling.
The position of the corpse also matters. Maggots are legless, worm-shaped larvae, so they tend to fall off surfaces that aren’t flat. If a body is lying down, decay it would be faster because the maggots wouldn’t fall off. If the zombie were walking, though, “they would be leaving a trail of maggots,” Miorelli says.
A cool environment can slow the process. Microbes and bugs alike work best in warm weather. Cold weather could help a zombie hold itself together for much longer — months or even years. “Antarctica, parts of Canada, that’s where zombies would be scary,” Miorelli says.
But Moran is reassuring. Even when dead bodies stay fresh, they won’t ever be coming for your brains. “If a person is truly dead ... there’s no shuffling after somebody,” Moran says. “If they’re shuffling, they’re not technically dead.”
So movies, books and games about the undead shouldn’t keep you up at night, she says. Biology and bugs have zombies well in hand. “You shouldn’t lose sleep over zombies.”
Technically Fiction is a blog that finds the science in the realm of the fantastic. Have a comment or a suggestion for a future post? Send an email to email@example.com.
alien A non-native organism. (in astronomy) Life on or from a distant world.
Antarctica A continent mostly covered in ice, which sits in the southernmost part of the world.
autolysis The destruction of cells or tissues by their own enzymes.
bacteria (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals).
beetle An order of insects known as Coleoptera, containing at least 350,000 different species. Adults tend to have hard and/or horn-like “forewings” which covers the wings used for flight.
biology The study of living things. The scientists who study them are known as biologists.
bug The slang term for an insect. Sometimes it’s even used to refer to a germ.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
corpse The body of a dead human. Also sometimes used to describe the remains of some inanimate object (such as a star).
diet The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health.
digest (noun: digestion) To break down food into simple compounds that the body can absorb and use for growth. Some sewage-treatment plants harness microbes to digest — or degrade — wastes so that the breakdown products can be recycled for use elsewhere in the environment.
egg The unfertilized reproductive cell made by females.
entomology The scientific study of insects. One who does this is an entomologist. A paleoentomologist studies ancient insects, mainly through their fossils.
environment The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).
enzymes Molecules made by living things to speed up chemical reactions.
forensics The use of science and technology to investigate and solve crimes.
gut An informal term for the gastrointestinal tract, especially the intestines.
host (in biology and medicine) The organism (or environment) in which some other thing resides. Humans may be a temporary host for food-poisoning germs or other infective agents.
insect A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.
liquid A material that flows freely but keeps a constant volume, like water or oil.
maggot The larva of a fly.
matter Something that occupies space and has mass. Anything on Earth with matter will have a property described as "weight."
microbe Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.
muscle A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.
nervous system The network of nerve cells and fibers that transmits signals between parts of the body.
organ (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.
organism Any living thing, from elephants and plants to bacteria and other types of single-celled life.
oxygen A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).
protein A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.
putrefaction The process of decay or rotting in a dead organism, especially when broken down by bacteria working without oxygen.
rigor mortis The stiffening of joints and muscles in a body a few hours after death.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
taste One of the basic properties the body uses to sense its environment, especially foods, using receptors (taste buds) on the tongue (and some other organs).
tendon A tissue in the body that connects muscle and bone.
virus Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.
waste Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.
weather Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.