Zombies Do Exist but They May Not Be as Scary as You Think They Are

Ghosts, demons, spirits… these are some of the supernatural creatures that our parents used to tell us about when we were a child. But are these creatures real? Is it scientifically possible for these creatures to exist? Well, probably not. Although these creatures might only be a myth, there is another type of creature which their existence may have already been proven through science… zombies.

In this spirit of Halloween, I have decided to write a fun and relaxed piece about zombies. From The Walking Dead to Resident Evil and to 28 Days Later, we all have a rough idea of what zombies are, how they look like, how they come into existence and how that then leads to a zombie apocalypse. But these ideas of zombies are only found in fictional, sci-fi movies.

Image: A scene from 28 Days Later. (Source: The Internet).

In reality, zombies are not exactly brain-eating creatures and they may not even appear as scary as the ones portrayed in films. The truth is, zombies already exist in the animal kingdom and they are probably wandering around in your backyard as you are reading this.

Mind-controlling parasites

As said above, zombies already exist in nature. Mind-controlling parasites are one of the factors that turns a healthy living animal into a zombie.

Zombie snails are probably one of the most common cases of zombie animals. This happens when a Succinea snail accidentally ingests the eggs of a parasitic worm called the green-banded broodsac (Leucochloridium paradoxum).

Once the eggs have been ingested by the snail, the eggs will hatch inside the body of the snail and the parasites will be released in their miracidium form (larval stage). The miracidia then develop into sporocysts (infectious stage), and the sporocysts will continue to reproduce asexually in the body of the snail to form more sporocysts.

Once the snail is infected, the sporocysts will travel all the way up to the snail eyes. This will make the snail eyes appear extremely large. The snail will also lose its motor control at this stage, as the mind of the snail has also already been controlled by the parasites.

The parasites will then make the snail move to an open area where it can be exposed to birds. The enlarged eyes of the snail will attract birds and will trick the birds to think that the eyes are worms.

When a bird catches and eats the snail, the parasites will enter the bird’s body and will develop into their adult form. They are then released through the bird faeces and new eggs will be laid on the ground. And the cycle continues when another healthy Succinea snail ingests the eggs.

Image: A Succinea snail that has been infected by Leucochloridium paradoxum. (Source: The Internet).

A similar act of mind-control can also be found in other animals such as the parasitic worm Spinochordodes tellinii in grasshoppers, the parasitic fungus Cordyceps sp. in ants and the parasitoid wasp Glyptapanteles sp. (in its larval form) in caterpillars.

Such cases happen predominantly in insects as insects do not have acquired immune system to fight against these parasites. Unlike humans and other mammals, insects do not possess antibodies. However, insects are not the only invertebrates that are vulnerable to mind-controlling parasites.

A mind-controlling activity caused by parasites can also be found in crustaceans such as the parasitic Sacculina barnacles in male mudcrabs. When a parasitic barnacle infects a male mudcrab, it will castrate the crab and cause the crab to grow a sac called externa. The externa is a female barnacle that carries eggs in her body.

The externa then attracts and will be fertilised by other male mudcrabs. The infected crab will then start to convince himself that he is a female mudcrab who is pregnant and he will start to take care of the fertilised eggs in the externa as if they are his children until they hatch. Once the eggs hatch, the parasites are released into the atmosphere and the cycle repeats.

Vertebrates are also not exempted from these mind-controlling parasites. A mind-controlling activity can be observed in frogs that are infected by the parasitic fungus Batrachochytrium dendrobatidis, and fish, birds and copepods that are infected by the parasitic worm Schistocephalus solidus. These parasites would manipulate their host behaviours for their own benefits.

Human mind-controlling parasites

What about humans, you ask? Well, let’s not have a sigh of relief yet because just like other animals above, we are not entirely safe from these mind-controlling parasites. The infection that happens in humans are caused by the protozoan parasite Toxoplasma gondii.

Studies have shown that the Toxoplasma parasites make rats and mice become unafraid of cats. If anything, they become even more attracted to cat urine after they have been infected by these parasites. This makes them become more vulnerable and more exposed to being preyed on by cats.

And as said earlier, Toxoplasma gondii can be infectious to humans too. And the result varies from being completely asymptomatic (has no symptoms) to being really severe. There have been cases where Toxoplasma gondii infection is reported to have links with mental illnesses such as schizophrenia and bipolar disorder. It can also cause suicidal tendencies in humans.

Most cases of mental illnesses caused by Toxoplasma gondii occur through a mother-to-child transmission. When a pregnant mother is infected with the parasites, she may not show any symptoms herself. But these parasites can be transmitted to the foetus in her womb and will cause the development of neurological disorders in the child once he or she is born.

These parasites can also cause serious neurological problems in people with a weakened immune system such as those who have autoimmune diseases or people living with AIDS.

How does the transmission of Toxoplasma parasites happen? Well, the answer is… cats. Toxoplasma parasites complete their life-cycle in cats. The parasites then release their eggs in the cats’ faeces.

Image: Cats are the definitive host of the Toxoplasma parasites. They have probably already plotted to rule the world a long time ago. (Image source: The Internet).

Toxoplasma gondii has infected 50% of the population worldwide. That’s more than 3.5 billion people that have being infected by these parasites! Unfortunately, an infection caused by Toxoplasma gondii has no cure, but fortunately, most of these cases appear to be asymptomatic.

One of the preventive measures that can be taken to prevent an infection caused by these parasites is to avoid giving your pregnant girlfriend or wife a cat as a present. Also, washing your hands with soap after patting or being licked by your cats would also be a good idea.

Infectious proteins

Mad cow disease, otherwise known as bovine spongiform encephalopathy (BSE), is a neurological disorder caused by the presence of misfolded proteins called prions in the central nervous system of a cow.

When humans eat the flesh of an infected cow, the prions from the meat will travel to the human brains and will subsequently cause a similar disease called the variant Creutzfeldt-Jakob disease (vCJD) or kuru in humans. This disease is mostly fatal.

Symptoms of vCJD include a personality change, slow bodily movement, muscle twitches, loss of coordination, the inability to speak, insomnia, and cognitive dysfunctions such as memory loss, confusion, delusion and hallucination. Sounds familiar?


In 1962, a Haitian man named Clairvius Narcisse, who was already dead, came back to life from his grave after he was cursed by a bokor or a Haitian Voodoo sorcerer. This incident has caused people to believe that Narcisse was raise from the dead. But did Narcisse really come back to life?

Two days prior to his death, Narcisse went to Albert Schweitzer Hospital where he reported to feel really sick. He had a really terrible fever and he felt a weird sensation all over his body, as if there were ‘bugs crawling underneath his skin’. The doctors diagnosed him with hypotension (low blood pressure) and pulmonary oedema (wet lungs).

On 2 May 1962, Narcisse was pronounced dead. His body stayed in the mortuary for 24 hours. His death was verified and his official death certificate was registered. His body was placed in a coffin and he was buried by his family in the graveyard. What happened next is eerie.

After everyone had left the burial ceremony, a bokor came to the graveyard and started digging Narcisse’s grave where the bokor claimed that he had cursed Narcisse. The bokor gave him a potion that turned him into a zombie slave, and he was then instructed by the bokor to work on a plantation together with other zombie slaves who were already waiting for his arrival.

Image: Clairvius Narcisse pointing at his own grave. (Source: The Internet).

After a thorough scientific examination, what was thought to be a curse that turned this man into a zombie was not really a curse. It was found out that the potion that turned Narcisse into a ‘zombie’ contained a combination of two neurotoxins that can be found in nature: tetrodotoxin (a puffer fish toxin) which causes severe paralysis that mimics death, and bufotoxin (a toad toxin) which is used as anaesthesia.

The potion also contained jimsonweed (Datura stramonium). This is the most important material in the equation that turned Narcisse into a lifeless zombie. Jimsonweed is a hallucinogenic herb which has a mind-controlling property and it also causes memory loss.

So, did Narcisse really rise from the dead? Nah, he was not even dead to begin with. The tetrodotoxin which paralysed Narcisse had tricked the doctors into believing that he was dead. And the bokor’s curse? It’s just science.

Synthetic drugs

Some drugs such as bath salts are known to alter people’s behaviours. A person who is under bath salts influence will show signs such as anxiety, rapid heart rate, seizures, cognitive dysfunctions, increased body temperature, panic attacks, hallucinations, violence and many more.

Bath salts also have the ability to turn a person into someone with superhuman strength. There was even a case where part of a teen’s face was eaten by Rudy Eugene who was under the influence of bath salts in Miami.

There is another drug that has similar effects to bath salts. It’s called flakka. Although flakka may not be as popular as bath salts, the effects are definitely much stronger. They call it a ‘zombie drug’ for a reason.

Flakka signs include extreme agitation, bizarre behaviours, rapid heart rate, and psychotic problems such as confusion, delusion and hallucination. Also, face-eating cannibalism, just as what happened to Austin Harrouff who ate his victims’ faces while he was under the influence of this drug.

To demonstrate how bad the effects of flakka can be, this video shows how people react under its influence:

Video showing people who are under the influence of flakka ‘zombie’ drug. (Source: https://youtu.be/BMJMujPoa4Y).

Zombie apocalypse

All the talk on zombies leads us to the next follow-up question — can a zombie apocalypse happen? And if it can, how are we going to survive it?

According to a study done by the researchers in the Department of Physics and Astronomy at the University of Leicester (yes, it is a legit scientific study!), when a zombie apocalypse occurs, it could wipe out humanity within just 100 days. And by that point, there will only be 181 uninfected people left on earth. The good thing is though, the zombies can only survive up to 20 days when they don’t have anything to feed on.

However, this model does not include geographical factors that could slow the zombies down, such as the mountains and the oceans. So, the researchers created another model where several measures were taken into account.

Suppose there were a 10% chance of killing a zombie when you meet them, and that the number of uninfected males and uninfected females were equal, and that half of the males and half of the females were capable of making babies, and that each female would be carrying one baby in three years; the number of uninfected people in this model increases from 181 to 200 million in 100 days.

But in this model, the lifespan of the zombies would also increase from 20 days to one year. And in 1000 days, the number of uninfected people will drop to 67 million. By this point, most of the zombies would have already died as there wouldn’t be as many uninfected people that they can feed on.

Six years after that, the zombies will be completely disappear from this earth and humanity will begin to grow again very slowly. Will you be one of the 0.0089% of the human population that will survive a zombie apocalypse?

Take-home message

Although zombies do exist in nature, they are not seen as near as the ones we often see in sci-fi movies. And despite the possibility of a zombie apocalypse to happen, just like aliens, the idea of flesh-eating zombies that transmit their pathogens by feeding on uninfected people that we see in the films are still just a hypothesis in science.

If there were any zombies that we need to be scared of, it would probably be ourselves. We spend so much time on our computers, phones and gadgets to the extent where we forget how to human. Reminds you of any zombie movies?

Image: Nicholas Hoult in Warm Bodies. (Source: The Internet).

Happy Halloween!