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Power Words
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algae Single-celled organisms, once considered plants (they aren't). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.

carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

carbon dioxide (or CO ₂) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they've eaten. Carbon dioxide also is released when organic matter (including fossil fuels like oil or gas) is burned. Carbon dioxide acts as a greenhouse gas, trapping heat in Earth's atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

chlorophyll Any of several green pigments found in organisms that perform photosynthesis - creating sugars (foods) from carbon dioxide and water.

chloroplast A tiny structure in the cells of green algae and green plants that contain chlorophyll and creates glucose through photosynthesis.

oxygen A gas that makes up about 21 percent of the atmosphere. All animals and many microorganisms need oxygen to fuel their metabolism.

pigment A material, like the natural colorings in skin, that alter the light reflected off of an object or transmitted through it. The overall color of a pigment typically depends on which wavelengths of visible light it absorbs and which ones it reflects. For example, a red pigment tends to reflect red wavelengths of light very well and typically absorbs other colors. Pigment also is the term for chemicals that manufacturers use to tint paint.

wavelength The distance between one peak and the next in a series of waves, or the distance between one trough and the next. Visible light - which, like all electromagnetic radiation, travels in waves - includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.

Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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Plants can make energy out of sunlight, all thanks to a pigment called chlorophyll.

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The moms of one spider species give new meaning to the idea of "self-serving." They feed themselves to their children.

The little cannibals get their start in life in a snug nest added to webs spun by their mom. The webs are a bit like ping-pong nets, explains Mor Salomon. She works at the Israel Cohen Institute for Biological Control in Yehud-Monosson, Israel. Salomon finds the webs of these spiders ( Stegodyphus lineatus) in shrubs along dry riverbeds in the Negev Desert in southern Israel. At one end of the web, a female spider spins a small cave. Inside it, she creates what looks like a tiny silk hockey puck holding 70 to 80 yellowish eggs.

Newly hatched spiderlings are trapped in the puck. Mom spider soon pierces the protective silk to free them. From them on, she never eats again. Her children, however, enjoy a gruesome feast.

For two weeks or so, Mom feeds her dozens of young by regurgitating a transparent liquid. Think of it as the soup course. This slurry mixes what's left of her last meals plus some of her own guts.

Preparation for this part of the meal starts early. The mother's midgut begins to break down while she is still guarding her eggs. And by the time the pale youngsters hatch, liquefied gut - suitable for baby mouthparts - is building up in her abdomen.

As the liquid spills onto Mom's face, the spiderlings swarm over her head. The babies form what looks like a face mask made of caramel-colored beads. Each female spider hatches only one brood in her lifetime. It's easy to understand why. Mom will regurgitate 41 percent of her body mass to feed her babies.

Those spiderlings don't stop there, either. Mom spider may even invite her offspring to gorge themselves. "She makes no attempt to escape," Salomon says. Eventually, the spiderlings pierce her abdomen with their mouthparts. The main dish is served. Over the course of several hours, the young drain her innards.

At the beginning of the feeding, Salomon says, "if you touch a leg, she will pull it back. She's definitely alive." By the end, the mother spider is clearly dead. All that is left is 4 percent of her original body mass.

The liquefaction process that makes this possible proceeds in an orderly way. Organs that are no longer needed dissolve. Among the organs that remain until the very end: mom's heart.

Salomon and her colleagues report their findings in the April Journal of Arachnology. (Arachnology is the study of spiders and related animals.)

Power Words

A group of invertebrate animals that includes spiders, scorpions, mites and ticks. Many have silk or poison glands. Arachnology is the study of these animals.

A genus of species that includes modern humans (Homo Homo sapiens). All had large brains and used tools. This genus is believed to have first evolved in Africa and over time its members continued to evolve and radiate throughout the rest of the world.

A perennial plant that grows in a generally low, bushy form.

spiderling An immature spider.

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Israel Cohen Institute for Biological Control

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The moms of one spider species give new meaning to the idea of "self-serving." They feed themselves to their children. The little cannibals get their start in life in a snug nest added to webs spun by their mom. The webs are a bit like ping-pong nets, explains Mor Salomon.

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Being infected with a parasite is usually not good news. These critters live in or on another. And they can sicken or even kill their hosts. When an animal has to deal with both a parasite and pollution, these stressors can add up. But that isn't true for Artemia brine shrimp, a new study finds. Infection with parasitic worms actually boosts the ability of these animals to survive in water laced with toxic arsenic.

Marta Sánchez works for the Spanish National Research Council in Seville. As an ecologist, she is interested in how living things relate to one another and to their environment. She studies the role of parasites. Her team was curious about brine shrimp because they are key players in their ecosystem. (That term refers to the collection of plants, animals and other things that live nearby.) Brine shrimp are crustaceans (Krus-TAY-shuns). They are eaten by many waterbirds, including flamingos. And those brine shrimp can ferry pollutants and parasites into the birds.

When brine shrimp are infected by parasites called tapeworms, they turn red. This makes them easy for birds to see. It also makes it easy for scientists to pick out the brine shrimp infected with worms..

And that's what Sánchez and her colleagues did.

They collected brine shrimp from the area where the Odiel and Tinto rivers in southwest Spain join before running into the Atlantic Ocean. Mining activities have tainted these waters with arsenic and toxic heavy metals. All of these elements are considered pollutants.

In the lab, the researchers separated brine shrimp into two groups. Some were infected with tapeworms; others were not. Then the scientists ran tests to see how well the tiny animals survived in polluted water.

As the level of arsenic in the water increased, so did the number of brine shrimp that died. But brine shrimp that were infected with worms survived better than uninfected ones did .

The researchers then ran their tests again. They were curious about how climate change might affect the brine shrimp's survival in polluted water. So this time they used warmer water. Again, worm infection seemed to protect the brine shrimp from the effects of arsenic.

The scientists reported their results March 3 in PLOS Pathogens.

It may seem strange that parasites would protect an animal's health. But causing its host to die quickly is not good for a parasite. It needs its host to stay alive long enough for the stowaway to reproduce and then move on to a new host. If that first host dies too quickly, so will the parasite. So helping brine shrimp survive polluted waters may be in the worms' best interest.

The worms may be helping to changing how their hosts deal with pollution and the stress it can cause. When the researchers compared infected and uninfected brine shrimp, they found differences. Infected brine shrimp had more droplets of lipids - fats - in their tissues. The lipid droplets may help the brine shrimp sock arsenic away so that it can't harm them.

Infected brine shrimp also produced more antioxidants. These are chemicals that protect an organism from the damaging effects of stress on cells. Stressors can include things like exposure to poisons. In the brine shrimp, "Infected individuals were better than uninfected individuals at coping under polluted conditions," Sánchez reports.

His team cannot say whether the beneficial link between tapeworms and brine shrimp is special to this spot in Spain. "What we can say," Sánchez notes, is that the reddening of organisms infected with tapeworms has been seen at sites in other countries. For that reason, she suspects brine shrimp in other places would show similar effects.

Power Words

antioxidant Any of many chemicals that can shut down oxidation - a biologically damaging reaction. They do this by donating an electron to a free radical (a reactive molecular fragment) without becoming unstable. Many plant-based foods are good sources of natural antioxidants, including vitamins C and E.

arsenic A highly poisonous metallic element. It occurs in three chemically different forms, which also vary by color (yellow, black and gray). The brittle, crystalline (gray) form is the most common. Some manufacturers tap its toxicity by adding it to insecticides.

brine shrimp Water-dwelling crustraceans in the genus Artemia. Some breeds of brine shrimp are sold as novelty items known as "sea monkeys."

cell The smallest structural and functional unit of an organism. Typically too small to see with the naked eye, it consists of watery fluid surrounded by a membrane or wall. Animals are made of anywhere from thousands to trillions of cells, depending on their size.

climate change Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

crustaceans Hard-shelled water-dwelling animals including lobsters, crabs and shrimp.

ecology A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

ecosystem A group of interacting living organisms - including microorganisms, plants and animals - and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.

element (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.

environment The sum of all of the things that exist around some organism or the process and the condition those things create for that organism or process. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature, humidity and placement of components in some electronics system or product.

host (in biology and medicine) The organism in which another lives. Humans may be a temporary host for food-poisoning germs or other infective agents.

infection A disease that can spread from one organism to another.

lipid A type of fat.

molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O ₂), but water is made of two hydrogen atoms and one oxygen atom (H ₂ O).

parasite An organism that gets benefits from another species, called a host, but doesn't provide it any benefits. Classic examples of parasites include ticks, fleas and tapeworms.

pathogen An organism that causes disease.

pigment A material, like the natural colorings in skin, that alter the light reflected off of an object or transmitted through it. The overall color of a pigment typically depends on which wavelengths of visible light it absorbs and which ones it reflects. For example, a red pigment tends to reflect red wavelengths of light very well and typically absorbs other colors. Pigment also is the term for chemicals that manufacturers use to tint paint.

pollutant A substance that taints something - such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.

stress (in biology) A factor, such as unusual temperatures, moisture or pollution, that affects the health of a species or ecosystem. (in psychology) A mental, physical, emotional, or behavioral reaction to an event or circumstance, or stressor, that disturbs a person or animal's usual state of being or places increased demands on a person or animal; psychological stress can be either positive or negative.

tapeworm A type of parasitic worm that infects people and other vertebrate animals. These host animals can become infected if they drink water or eat food that contains tapeworm eggs or larvae. Ingesting tapeworm eggs can lead to infection in body tissues and organs. This can cause serious illness. Adult tapeworms, which develop after an organism injects tapeworm larvae (not eggs), live in the intestines of their hosts. They have long, ribbonlike bodies. Intestinal tapeworm infections can last for many years, usually causing only mild symptoms.

tissue Any of the distinct types of material, comprised of cells, which make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues. And brain tissue will be very different from bone or heart tissue.

toxic Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.

waterbird A bird that lives in or near water.

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Parasites give brine shrimp super powers

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Being infected with a parasite is usually not good news. These critters live in or on another. And they can sicken or even kill their hosts. When an animal has to deal with both a parasite and pollution, these stressors can add up. But that isn't true for Artemia brine shrimp, a new study finds.

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A zombie crawls through the forest. When it reaches a good spot, it freezes in place. A stalk slowly grows from its head. The stalk then spews out spores that spread, turning others into zombies.

This is no Halloween story about the zombie apocalypse. It's all true. The zombie isn't a human, though. It's an ant. And the stalk that emerges from its head is a fungus. Its spores infect other ants, which lets the zombie cycle begin anew.

In order to grow and spread, this fungus must hijack an ant's brain. However weird this might seem, it isn't all that unusual. The natural world is full of zombies under mind control. Zombie spiders and cockroaches babysit developing wasp larvae - until the babies devour them. Zombie fish flip around and dart toward the surface of the water, seeming to beg for birds to eat them. Zombie crickets, beetles and praying mantises drown themselves in water. Zombie rats are drawn to the smell of the pee of cats that may devour them.

All of these "zombies" have one thing in common: parasites. A parasite lives inside or on another creature, known as its host. A parasite may be a fungus, a worm or another tiny creature. All parasites eventually weaken or sicken their hosts. Sometimes, the parasite kills or even eats its host. But death of the host isn't the freakiest goal. A parasite might get its host to die in a certain place, or be eaten by a certain creature. In order to accomplish these tricks, some parasites have evolved the ability to hack into the host's brain and influence its behavior in very specific ways.

How do parasites turn insects and other animals into the walking almost-dead? Every parasite has its own method, but the process usually involves altering chemicals within the victim's brain. Researchers are working hard to identify which chemicals are involved and how they end up so bizarrely altering their host's behavior.

Brains, brains! Ant brains!

A fungus doesn't have a brain. And worms and single-celled critters obviously aren't very smart. Yet somehow they still control the brains of larger, and smarter, animals.

"It blows my mind," says Kelly Weinersmith. She is a biologist who studies parasites at Rice University in Houston, Texas. She is particularly interested in "zombie" creatures. True zombies, she points out, aren't exactly like the type you find in horror stories. "In no way are these animals coming back from the dead," she says. Most real zombies are doomed to die - and some have very little control over their actions.

The horsehair worm, for instance, needs to emerge in water. To make this happen, it forces its insect host to leap into a lake or swimming pool. Often, the host drowns.

Toxoplasma gondii (TOX-oh-PLAZ-ma GON-dee-eye) is a single-celled creature that can only complete its life cycle inside a cat. But first, this parasite must live for a time in a different animal, such as a rat. To ensure this part-time host gets eaten by a cat, the parasite turns rats into cat-loving zombies.

In Thailand, a species of fungus - Ophiocordyceps - can force an ant to climb almost exactly 20 centimeters (about 8 inches) up a plant, to face north and then to bite down on a leaf. And it makes the ant do this when the sun is at its highest point in the sky. This provides ideal conditions for the fungus to grow and release its spores.

Biologist Charissa de Bekker wants to better understand how that fungus exerts that mind control over the ants. So she and her team have been studying a species related to the Ophiocordyceps fungus in Thailand. This U.S. cousin is a fungus native to South Carolina. It, too, forces ants to leave their colonies and climb. These ants, though, bite down on twigs instead of leaves. This is likely due to the fact that trees and plants in this state lose their leaves in the winter.

De Bekker began these studies at Pennsylvania State University in University Park. There, her team infected a few species of ant with the South Carolina fungus. The parasite could kill all of the different ants she introduced to it. But the fungus made plant-climbing zombies only out of the species that it naturally infects in the wild.

To figure out what was going on, de Bekker's team collected new, uninfected ants of each species. Then, the researchers removed the insects' brains. "You use forceps and a microscope," she says. "It's sort of like that game Operation."

The researchers kept the ant brains alive in small Petri dishes. When the fungus was exposed to its favorite brains (that is, ones from the ants that it naturally infects in the wild), it released thousands of chemicals. Many of these chemicals were completely new to science. The fungus also released chemicals when exposed to unfamiliar brains. These chemicals, however, were completely different. The researchers published their results in 2014.

The experiments at Penn State by de Bekker's team were the first to create ant zombies in the lab. And the researchers only succeeded after setting up artificial 24-hour cycles of light and darkness for the zombies and their parasites.

It will take more work to learn how the parasite's chemicals lead to zombie behavior in ants. "We are very much in the beginning of trying to figure this out," says de Bekker. She now studies ant zombies at Ludwig Maximilian University in Munich, Germany. There, she is now probing how that daily cycle of sunlight and darkness affects zombification.

Soul-sucking wasps

Of all parasites, wasps know some of the creepiest tricks. One wasp, Reclinervellus nielseni, lays its eggs only on orb-weaving spiders. When a wasp larva hatches, it slowly sips its host's blood. The spider stays alive long enough to spin a web. But not just any web. It spins a nursery of sorts for the wriggly, worm-like wasp baby stuck to its back.

The spider will even break down its old web to start a new one for the larva. "The [new] web is stronger than the normal web," explains Keizo Takasuka. He studies insect behavior and ecology at Kobe University in Japan. When the web is done, the larva eats its spider host.

Now the larva spins a cocoon in the middle of the web. The extra strong threads most likely help the larva stay safe until it emerges from its cocoon 10 days later.
Story continues after video.

In this video, the zombie spider has finished weaving an extra strong web for the wasp larva. The larva then eats the spider's insides and spins itself a cocoon.

The jewel wasp puts an insect on the menu it serves up to its young: cockroach. But before a wasp larva can chow down, its mother needs to catch a bug that's twice her size. To do this, says Frederic Libersat, "she transforms the cockroach into a zombie." Libersat is a neurobiologist who studies how the brain controls behavior. He works at Ben Gurion University in Beer-Sheva, Israel.

The jewel wasp's sting takes away a cockroach's ability to move on its own. But it follows like a dog on a leash when the wasp pulls on its antenna. The wasp leads the cockroach to her nest and lays an egg on it. Then she leaves, sealing the egg inside the nest with its dinner. When the egg hatches, the larva slowly devours its host. Being a zombie, this cockroach never tries to fight back or escape.

This scenario is so creepy that biologists named a similar wasp Ampulex dementor - after a supernatural enemy in the Harry Potter series. In these books, dementors can devour people's minds. This leaves the victim alive but without a self or soul. (Although A. dementor is a close relative of the jewel wasp, Libersat notes that researchers have not yet confirmed that it also turns cockroaches or any other insect into mindless slaves.)

Libersat's group has focused its research on figuring out what the jewel wasp does to the cockroach mind. The mother jewel wasp performs something like brain surgery. She uses her stinger to feel around for the right part of her victim's brain. Once found, she then injects a zombifying venom.

When Libersat removed the targeted parts of a roach's brain, the wasp would feel around what was left of the roach's brain with her stinger for 10 to 15 minutes. "If the brain was present, [the wasp] would take less than a minute," he notes. This shows that the wasp can sense the right place to inject its poison.

That venom might interfere with a chemical in the roach's brain called octopamine, Libersat reports. This chemical helps the cockroach stay alert, walk and perform other tasks. When researchers injected a substance similar to octopamine into zombie cockroaches, the insects again began walking.

Libersat cautions, however, that this is likely just one piece of the puzzle. There is still work to do to understand the chemical process happening in the cockroach's brain, he says. But Weinersmith, who was not involved in the research, notes that Libersat's team has worked out this chemical process in more detail than is available for most types of zombie mind control.

Brain worms

Weinersmith's specialty is zombie fish. She studies California killifish infected with a worm called Euhaplorchis californiensis (YU-ha-PLOR-kis CAL-ih-for-nee-EN-sis). A single fish may have thousands of these worms living on the surface of its brain. The wormier the brain, the more likely the fish is to behave strangely.

"We call them zombie fish," she says, but admits that they are less like zombies than the ants, spiders or cockroaches. An infected fish will still eat normally and stay in a group with its pals. But it also tends to dart toward the surface, twist its body around or rub against rocks. All of these actions make it easier for birds to see the fish. Indeed, it's almost like the infected fish wants to get eaten.

And that's precisely the point, says Weinersmith - for the worm. This parasite can only reproduce inside a bird. So it alters the fish's behavior in a way that attracts birds. Infected fish are 10 to 30 times more likely to get eaten. That's what Weinersmith's colleagues Kevin Lafferty of the University of California, Santa Barbara and Kimo Morris of Santa Ana College in California discovered.

Weinersmith now is working with Øyvind Øverli at the Norwegian University of Life Sciences, in As. They are studying the chemical processes behind the zombie fish's bird-seeking behavior. So far, it seems that zombie fish may be less stressed out than their normal cousins. Researchers know what chemical changes should happen to a killifish brain when something, such as the sight of a bird on the prowl, stresses it out. But in a zombie fish's brain, these chemical changes don't seem to occur.

It's as if the fish notices the hunting bird but doesn't get freaked out as it should. "We need to do further studies to confirm this is true," says Weinersmith. Her group plans to analyze the chemicals in the brains of infected fish, then try to recreate the zombie effect in normal fish.

Success won't come easily. Zombie mind control is a complicated matter. Parasites have developed their control of other creatures' brains over millions of years of evolution. Scientists have found fossil evidence of fungus-controlled ants dating back 48 million years. Over this long period, she says, "the fungus 'learned' a lot more about how the ant's brain works than human scientists have."

But scientists are starting to catch up. "Now we can ask [the parasites] what they've learned," quips Weinersmith.

Ant brains may be much simpler than human brains, but the chemistry going on inside them isn't all that different. Figuring out the secrets of zombie mind control in bugs could help neuroscientists understand more about the links between the brain and behavior in people.

Eventually, this work could lead to new medicines or therapies for human brains. We just have to hope that a mad scientist won't go out and start making human zombies!

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antenna (plural: antennae) In biology: Either of a pair of long, thin sensory appendages on the heads of insects, crustaceans and some other arthropods.

behavior The way a person or other organism acts towards others, or conducts itself.

birds Warm-blooded animals with wings that first showed up during the time of the dinosaurs. Birds are jacketed in feathers and produce young from the eggs they deposit in some sort of nest. Most birds fly, but throughout history there have been the occasional species that don't.

bug The slang term for an insect. Sometimes it's even used to refer to a germ.

chemical A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H ₂ O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.

chemistry The field of science that deals with the composition, structure and properties of substances - chemicals - and how they interact. Chemists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances.

colleague Someone who works with another; a co-worker or team member.

ecology A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.

evolution (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more "advanced," just better adapted to the conditions in which it developed.

fossil Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called "body fossils." Things like footprints are called "trace fossils." Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.

fungus (plural: fungi) One of a group of single- or multiple-celled organisms that reproduce via spores and feed on living or decaying organic matter. Examples include mold, yeasts and mushrooms.

host (in biology and medicine) The organism in which another lives. Humans may be a temporary host for food-poisoning germs or other infective agents.

infect To spread a disease from one organism to another. This usually involves introducing some sort of disease-causing germ to an individual.

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.

larva (plural: larvae) An immature life stage of an insect, which often has a distinctly different form as an adult. (Sometimes used to describe such a stage in the development of fish, frogs and other animals.)

life cycle The succession of stages that occur as an organism grows, develops, reproduces - and then eventually ages and dies.

link A connection between two people or things.

microscope An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.

neurobiologist Scientist who studies cells and functions of the brain and other parts of the nervous system.

parasite An organism that gets benefits from another species, called a host, but doesn't provide it any benefits. Classic examples of parasites include ticks, fleas and tapeworms.

Petri dish A shallow, circular dish used to grow bacteria or other microorganisms.

physical (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).

scenario An imagined situation of how events or conditions might play out.

species A group of similar organisms capable of producing offspring that can survive and reproduce.

spider A type of arthropod with four pairs of legs that usually spin threads of silk that they can use to create webs or other structures.

spore A tiny, typically single-celled body that is formed by certain bacteria in response to bad conditions. Or it can be the single-celled reproductive stage of a fungus (functioning much like a seed) that is released and spread by wind or water. Most are protected against drying out or heat and can remain viable for long periods, until conditions are right for their growth.

supernatural Something that is attributed to unnatural forces, such as gods or ghosts.

venom A poisonous secretion of an animal, such as a snake, spider or scorpion, usually transmitted by a bite or sting.

Kathryn Hulick is a freelance science writer and the author of Strange But True: 10 of the World's Greatest Mysteries Explained, a book about the science of ghosts, aliens and more. She loves hiking, gardening and robots.

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A zombie crawls through the forest. When it reaches a good spot, it freezes in place. A stalk slowly grows from its head. The stalk then spews out spores that spread, turning others into zombies. This is no Halloween story about the zombie apocalypse. It's all true. The zombie isn't a human, though.