Zombie Parasites

Meet The Parasites That Turn Their Hosts Into Zombies

Table of Contents

What are parasites?

There are a whole range of organisms that live as parasites. This means that they live off another organism. We are familiar with some common parasites. These include ticks, fleas, and worms in our guts. There are some parasites that control the brain of their host. They turn that host into a so-called “zombie.”

Adult Deer Tick, Ixodes scapularis. Ticks are an example of a parasite. They live off another
Adult Deer Tick, Ixodes scapularis. Ticks are an example of a parasite. They live off another, Credit: Wikimedia/Scott Bauer

How can parasites control their hosts?

Massospora is a type of fungus that can infect its prey and take over its mind. This is why it has been given the name “zombie fungus.” The fungus uses mind control in order to get the insect to do what it wants. 

Periodical cicadas are incredible insects. They emerge from underground only once in 13 or 17 years. They often fall prey to these fungi. The fungal spores land on the cicada. They begin devouring its abdomen. This provides nourishment for the fungus. Its main objective, however, is to spread its spores to others.

A cicada infected with Massospora fungus
A cicada infected with Massospora fungus, Credit: Wikimedia/G. Edward Johnson

It releases psychoactive substances such as psilocybin, which is found in hallucinogenic mushrooms. It affects the insect’s brain and nervous system, changing their behavior. The cicadas fly around, spreading the fungal spores further. Infected males begin to make female mating calls, attracting more males as they sing. When the males try to mate with the infected cicadas, they, too, become infected. 

This gruesome discovery is tragic for insects like the cicada. However, scientists believe it could help us. We could tackle problems caused by insects. If we can use something, such as fungus, to change insect behavior, we may be able to control them. Where insects cause crop damage or harbor diseases, we may be able to combat this with fungal infiltration. 

Quite a few parasites use multiple hosts to complete their life cycles. Take malaria, for example. This parasite requires both mosquitoes and humans to survive. Although it does not use mind control, it shows how important a range of hosts are to its survival. Malaria has a complex life cycle and thrives in multiple hosts. This makes developing a malaria vaccine challenging. 

Are there other examples of mind controlling parasites?

Massospora is not the only use of mind control in nature. As well as “zombie fungi,” there are also “zombie worms.” Some snails can become infected by a parasite called Leucochloridium paradoxum, or L. paradoxum. This parasite invades the snail’s tentacles. It changes the appearance and behavior of the snail. The tentacles become swollen and colourful. They pulsate to attract birds by mimicking caterpillars.

The snail’s tentacles look like a caterpillar when infected by L. paradoxum
The snail’s tentacles look like a caterpillar when infected by L. paradoxum, Credit: Wikimedia/Thomas Hahmann

It also reduces the snail’s ability to react to light intensity. Normally the snail would seek shelter in shadowy places. It does this to avoid predation. When infected with the parasite, however, they slither about in the light. The infected snails make their way to the tops of foliage, which makes them more visible to predators. Easily spotted, they are eaten by birds. The parasite reproduces inside the bird. Its eggs are then released in the bird’s feces. This completes the life cycle of this parasite

Other parasites are known to work in a similar way. Toxoplasma is a parasite found in cat feces. Pregnant women are especially warned to be careful around cats and their feces. The parasite can be dangerous for their unborn child.

Toxoplasma also has different life stages, requiring different host species. The parasite can only reproduce inside cat intestines. This is a very specific host. 

Cats often eat rats. So, the parasite has found a way to change the behavior of rats, to make the rats more susceptible to predation by cats. The parasite affects the brain, making them less afraid of the smell of a cat. Usually, a rat will run and hide when it smells a cat. Being infected with Toxoplasma, however, makes the rats more bold and less likely to run from a cat. As a result, the rats are easily eaten by the cats. The ingested parasite can then complete its life cycle inside the cat’s intestines.

When infected with Toxoplasma, rats become fearless
When infected with Toxoplasma, rats become fearless, Credit: Wikimedia/Zeynel Cebeci

Can these mind-controlling parasites affect humans?

The parasite affects the part of the brain associated with fear. Making the rodents fearless is key to the parasite’s survival. This effect has been shown in humans. It is thought that a third of humans are infected with Toxoplasma.

In humans, toxoplasmosis is associated with schizophrenia, suicide attempts and road rage. These are negative and devastating associations with the parasite. However, there are also positive behaviors resulting from toxoplasma infection. 

Scientists found that infected individuals were less fearful. They were more likely to take risks. They reported little or no fear of failure. In the world of business and economics, this presented itself as an entrepreneurial attitude. Many of these people were successful and had started their own businesses.

Human behavior is complex, and altered by many different things. Knowing that a parasite can affect the way you behave is incredible. It can change the way you think. It can change the way you act. It’s amazing how these microscopic organisms can alter our way of life.


Parasites: An organism living in or on another, from which it obtains its nutrients

Psychoactive: A substance that affects the brain, changing thoughts, feelings, and behavior

Spores: A reproductive cell produces by fungi, bacteria, and some plants

Schizophrenia: A mental disorder in which people view reality differently

Entrepreneurial: Taking financial risks in hope of large profits

Flesch Kincaid Grade Level: 7

Flesch Kincaid Reading Ease: 61.7

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2. Goedknegt, A., Welsh, J., & Thieltges, D. W. (2012). Parasites as prey. eLS.


3. Wesołowska, W., & Wesołowski, T. (2014). Do L. eucochloridium sporocysts manipulate the behaviour of their snail hosts?. Journal of Zoology, 292(3), 151–155.


Vyas, A., Kim, S. K., & Sapolsky, R. M. (2007). The effects of Toxoplasma infection on rodent behavior are dependent on dose of the stimulus. Neuroscience, 148(2), 342–348.


4. Vyas, A. (2015). Mechanisms of host behavioral change in Toxoplasma gondii rodent association. PLoS pathogens, 11(7), e1004935.


5. Desmettre, T. (2020). Toxoplasmosis and behavioural changes. Journal Francais d’Ophtalmologie, 43(3), e89–e93.


6. Johnson, S. K., Fitza, M. A., Lerner, D. A., Calhoun, D. M., Beldon, M. A., Chan, E. T., & Johnson, P. T. (2018). Risky business: linking Toxoplasma gondii infection and entrepreneurship behaviours across individuals and countries. Proceedings of the Royal Society B: Biological Sciences, 285(1883), 20180822.

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  • Kate Lewis, Ph.D.

    I studied for my BSc Zoology degree in Swansea University, UK in 2009 and competed my PhD in Agriculture in 2014 at Aberystwyth University, UK. I'm passionate about science, in particular zoology. I've worked in research for over 10 years. This work is usually broad and extensive. It has involved finding solutions to problems associated with farming, antibiotic resistance, animal and human nutrition, and reducing the impact of agriculture on climate change. I have had the pleasure of working both in the UK and overseas. My most enjoyable project to date, has been working along the African Rift Valley. I love talking about these topics and trying to convey my enthusiasm for them through scientific writing. Writing for Smore Magazine allows me to do that.