Real-Life Zombies: Parasites invaded these four animals and turned them into the living dead.
This scene happens only in horror movies. But something just as spooky sometimes takes place in real life. Weird life-forms called parasites can invade the brains of living animals. They can control the behavior of their hosts, turning them into real-life zombies! Their victims include insects, rodents, and snails.
The nightmare begins when a parasite invades an animal's body. It steals nutrients from its host to feed itself. Then the parasite creeps into the brain of its victim. It forces the animal to do things that help the parasite but harm the host.
Many mind-controlling parasites are made up of only one cell, says Susan Perkins. She studies parasites at the American Museum of Natural History in New York City. "It's creepy how these tiny creatures can change the way their host looks and acts," she says.
Read on to meet four mind-controlling parasites and their zombie hosts--if you dare!
This ant didn't grow a horn. That long stalk is part of a parasitic fungus. It invades an ant's body and leads the insect to its doom.
The takeover starts when a tiny fungus cell called a spore lands on the ant. The spore burrows through the insect's hard outer shell. Inside the ant's body, cells from the fungus multiply. Scientists think the fungus releases substances that control the insect's behavior.
Under the influence of the fungus, the ant begins to act strangely. It leaves its feeding area on the ground and climbs up onto a branch. It bites down on the branch, clamping itself in place. This isn't for the ant's benefit. It's the perfect spot for the fungus to find its next victim.
Within hours, the ant dies. The fungus bursts out of the insect's body and releases a shower of spores. That's bad news for any ants crawling below it. They may become the parasite's next zombie hosts!
Caption: Mind-controlling fungus
The fungus forces the ant to bite down on a branch before the ant dies.
What's weirder than a slimy snail? How about a snail infested with mind-controlling worms?
These garden snails fell victim to a parasitic flatworm. This happens when snails eat bird poop with flatworm eggs inside (see A Parasite's Life, right). Baby flatworms hatch and creep into the snail's brain. Then they invade its eyes. The parasites make the snail's eyes look like wiggly caterpillars--a nice snack for birds.
Snails usually avoid well-lit locations, where predators can easily spot them. But zombie snails move out into the open. Scientists think that's because the parasite releases a chemical that changes how the snail behaves.
Birds see the tasty-looking eye stalks and bite them off the snail. The worm infects the bird, and the cycle begins again. But for the snail, the worst is over--its eyes grow back!
Caption: Normal eye
Eye infested with parasitic worms
Is this rat out of its mind? Most rats avoid cats so they don't get eaten. But not rats infested with the microbe Toxoplasma gondii (tok-soh-PLAZ-muh GOHN-dee-eye). Infected rats find the smell of cat urine irresistible. They follow felines around!
T. gondii can reproduce only inside a cat's gut. To get there, it first infects a rodent. Rats pick up the parasite by eating cat droppings. Then the parasite brainwashes its host.
Scientists think the parasite changes the rodent's brain to make it less afraid of cats. This zombie rat is easy prey for a hungry feline. Once a cat catches and eats the rat, the microbe can multiply--and spread to its next victims.
Caption: This microscopic parasite makes rats less afraid of cats.
A Parasite's Life
The flatworm that attacks snails has two different hosts during its life cycle.
(1) A snail eats bird droppings that have flatworm eggs inside.
(2) Flatworms grow in the snail's gut. Some move into its eye stalk.
(3) The eye stalk swells up. A bird thinks the eye is a caterpillar and eats it.
(4) The flatworms lay eggs in the bird's gut. The bird poops out the eggs.
Think: What are the advantages and disadvantages of being a parasite?
This ladybug is protecting a baby insect. But the offspring isn't its own. It's the larva of a parasitic wasp that forces ladybugs to guard its young.
The spooky wasp first stings a ladybug to inject an egg. The larva grows inside the bug's body, sapping nutrients from its host.
Weeks later, the larva burrows out of the ladybug. It weaves a cocoon around itself and starts to develop into an adult. Suddenly, the ladybug becomes paralyzed. Scientists think the mother wasp injects a virus that attacks the ladybug's brain.
As the young wasp matures, the helpless ladybug guards it from predators. A week later, an adult wasp emerges and flies off. Most ladybugs die at this point. But some live--and may become zombie parents again!
Caption: Parasite larva
words to know
parasite--an organism that lives on or inside another organism and often harms its host
host--the organism that a parasite lives on or inside
cell--the smallest unit of a living thing
fungus--an organism, such as a mold or a mushroom, that looks plant-like but has no leaves or roots
life cycle--the series of changes a living thing goes through from birth to death
larva--the wormlike young of an insect or other animal
READING LEVELS: Lexile 810 / Guided Reading Level R
NEED A LOWER READING LEVEL? To access this article at a lower reading level, go to superscience.scholastic.com.
Compare and contrast the life cycle of a parasite with those of other organisms, including other parasites.
Core Idea: LS1.B: Growth and development of organisms
Practice: Obtaining, evaluating, and communicating information
Crosscutting Concept: Patterns
Writing: 2. Write explanatory text to convey ideas and information clearly.
Science: 3.10C, 4.10C, 5.9A, 6.12E
ELA: 3.21,4.19,5.19, 6.18
(1) Review the concept of life cycles, which may vary from one organism to another.
Display a diagram of a life cycle that students are likely familiar with, e.g., butterfly, chicken, or frog life cycle.
Divide students into small groups and ask each group to create a life cycle diagram for another familiar plant or animal. You can assign each group a life cycle to research in books or online. Ask students to discuss and record what they notice about their life cycle diagram.
Have groups share their diagrams with the class. As a class, discuss similarities and differences between the life cycles.
(2) Define parasites and hosts as an introduction to the article.
Display the words parasite and host and explain what each word means. Tell students that parasites have special life cycles. For at least part of their life, they depend on a host for food, shelter, or to reproduce.
Ask students to identify examples of organisms that are parasites and organisms that serve as hosts. (Parasites include ticks, fleas, hookworms or ringworms, and oxpeckers. Hosts include deer, cats, dogs, and humans.)
(3) Read the article and use a skills sheet to organize information from the story.
Distribute the skills sheet "Parasitic Pairs" on page T5. Tell students they will read about some different types of parasites and the effects they have on their hosts. Have students read the article in small groups or with a partner. As students read the article, they should use the skills sheet to record important information that explains the relationship between each type of parasite and its host.
(4) Share information with others.
To communicate information from the article, students should find someone in the room they have not worked with and share their worksheets. Have students discuss their findings and ask each other questions about the information they gathered. Students should compare and contrast the pairs, looking for patterns.
available at scholastic.com/supersrience
Parasitic Pairs (T5): Organize information from the article in a table.
Think It Through (T13): Answer critical-thinking questions about the article.
Build a Parasite (online only): Describe an imaginary parasite inspired by the article.
Snail Zombies (online only): Learn about a parasitic worm and its hosts.
Parasitic Pairs In "Real-Life Zombies" (pp. 4-7), you will read about several parasites and the ways they affect their hosts. Use the space below to describe the parasites and hosts that you read about. When you're done, share with a partner. We've done the first one for you. Organisms What does the parasite do? Parasite: fungus A fungus spore lands on an ant. The fungus grows inside of the ant. It makes the ant climb. Then Host: ant the fungus bursts out and releases spores. Parasite: Host: Parasite: Host: Parasite: Host: Organisms What happens to the host? Parasite: fungus The ant gets infected by a fungus spore. The ant climbs up a branch and bites it to hold on. The Host: ant ant dies when the fungus grows out of it. Parasite: Host: Parasite: Host: Parasite: Host: DISCUSS: What do these parasitic relationships have in common?
DISCUSS: What do these parasitic relationships have in common?
* Parasitic Pairs (Reproducible, T5)
Answers will vary slightly but should include these details from the perspective of host or parasite: Parasite: flatworm. Host: snail. The flatworm gets eaten by a snail. It infects the snail's eye and makes it look like a caterpillar. The snail goes out into the open to get attacked by birds.
Parasite: Toxoplasma gondii. Host: rat. The microbe lives in cat droppings and gets eaten by a rat. It makes the rat less afraid of cats. The rat gets eaten by a cat. Parasite: wasp larva. Host: ladybug. An adult wasp injects an egg into a ladybug. The larva burrows out and weaves a cocoon. The ladybug is paralyzed and shields the cocoon.
(Note: Students may notice that birds and cats are also hosts for these parasites. However, their behavior is not affected in a similar manner.)
Think It Through
Directions: Read each question below, then use the article "Real-Life Zombies" (pp. 4-7) to answer them.
1. According to the article, parasites invade a host's body and cause harm. Write two sentences that support this statement and explain the types of harm done.--
2. Look at the diagram of the parasitic flatworm's life cycle on page 7. Identify the host(s) of the flatworm.
(A) a bird and bird droppings
(B) only a snail
(C) a bird and a snail
(D) only a bird
3. On page 7, the author describes an infected ladybug and states, "Weeks later, the larva burrows out of the ladybug." Which of the following is closest to the meaning of the word burrows in that sentence?
(A) to get stuck
(B) to look through
(C) to eat
(D) to make a hole or passage
4. In your own words, summarize the main idea of the article.--
5. Imagine that you are one of the parasites mentioned in the article. Write a diary entry describing your journey through one of your hosts. Include at least two facts from the article that describe how you enter the host's body and how your host is affected. (If you need more room, continue your entry on the back of this page.)
Level Any Feature Article in the Digital Edition--
Need to differentiate for your students? Use our online leveling tool to view and print leveled-down versions of all four feature articles in the digital edition of SuperScience. Using the leveling feature is easy. Just follow these steps:
(1) Log in to scholastic.com/superscience and active your digital resources if you haven't done so already. (See page T2 of this Teacher's Guide for instructions.)
(2) The homepage will list the most recent issue, along with its features.
(3) Click on the story you're interested in reading.
(4) Click on the Reading Level drop-down menu and select the appropriate level for your students.
Reading levels are listed in the standards chart on page Hand at the top of each lesson plan in this Teacher's Guide.
1. Details may include: Some hosts die or get eaten after a parasite infects them. The snails have their eyes eaten, but they can grow back. 2. c 3. d 4. Parasites can invade other organisms and change the behavior of their hosts. 5. Answers will vary.
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