10 Bizarre Parasites and Their Petrifying Ways of Taking Over Their Hosts



We have heard of parasites and how they can feed off another organism, nourishing itself while devoiding the host of nourishment. They can be dangerous—as dangerous as bringing about a drastic environmental change or causing the death of a human being. On Earth, there are many bizarre parasites that can do things that are like themes in our nightmares.  The word “parasite” comes from the Greek word “parasitos” which was a term for a person who is eating at another’s table. “Parasitos” is a combination of the two Greek words “para” which means “alongside” and “sitos” which means “food.” Here is a list of some bizarre parasites and their dangerous ways.

1. Toxoplasma gondii is a brain parasite spread through cat feces can be transmitted to humans. It can cause humans to care for their cats excessively along with causing several neurological disorders. It brings about a “fatal attraction” in mice towards cats and slows them down, making them easy prey.

Image credits: Jitinder P. Dubey/ars.usda, pixabay

Found across the globe, Toxoplasma gondii (T. gondii) is known to have affected 50-80% of the human population at some point in time according to serological studies. In France, the highest concentration of infected persons (84%) has been found. It can affect all warm-blooded animals but can multiply only through cats. This deadly parasite is known to cause the same alterations in a human mind as it causes in mice. When mice are infected after ingesting the oocysts (the offspring of the parasites) shed in the feces of the cats, their guard is let down making them less risk-averse and they become slow and are an easy prey for cats. To make matters worse, the fear in the minds of the hosts, including mice, vanishes causing the “fatal attraction phenomenon” where the mice are attracted to the cat’s odor. Even male humans who were infected found the odor of cat urine to be “more pleasant” than the ones who were not infected. In women, the effect was the opposite.

In humans, this parasite can cause several pathological behavioral alterations and serious neurological disorders such as schizophrenia, obsessive-compulsive disorder, aggression, and bipolar disorder. In healthy individuals, it produces mild flu-like symptoms, but in infants and patients with weak immunity, it can cause a disease called “toxoplasmosis” which can be fatal. It makes humans love and care for their cats more than usual, and that is the reason why toxoplasmosis is dubbed as the “Crazy Cat Lady Syndrome.” It could be a reason why some people obsess over cats. (1,2)

2. Cymothoa exigua is a parasite that severs the blood vessels of a fish’s tongue and becomes a new functional tongue itself. It is the only known parasite to replace an entire organ in the host organism.

Image credits: Marco Vinci/wikipedia

Also known as “tongue-eating louse,” Cymothoa exigua (C. exigua) enters a fish’s body through its gills. The male attaches itself to the arches beneath fish’s gill and the female attaches itself to the fish’s tongue. This 8-29-millimeter-long parasite severs the blood vessels of the fish’s tongue causing it to atrophy from lack of blood, eventually making it fall of its mouth. C. exigua then becomes the fish’s new tongue and feeds on the fish’s blood and mucus to survive. When the fish dies, it detaches itself and hangs on the outside of the fish’s body. What happens to the parasite after that is not known. Another striking feature of this parasite aside from it being the only known one to replace an entire organ of its host is that the male can turn into a female once it becomes 10 millimeters long.

Found in the waters of the south of Gulf of California to the north of Gulf of Guayaquil, Ecuador, the parasite is also found in Atlantic waters. C. exigua is not believed to be harmful to humans currently unless the parasite is picked up alive by a human. When that happens, it can bite a person. It is a shocking fact that isopods like C. exigua are often found attached to aquatic animals and consumed by humans regularly. They are not poisonous to humans. (source)

3. Phronima is the alien in the movie Alien which was inspired by a transparent, deep-sea parasite that eats other creatures from the inside out and then takes over their bodies to ride the seas in the carcass and lay its eggs.

Phronima adds more weight to the saying “truth is stranger than fiction.” This parasite, more technically, a “parasitoid,” inspired the fictional, extraterrestrial species character who is the antagonist in the movie series AlienPhronima is found throughout the world’s oceans except in the polar region and is unique. The female, which attacks the salps (a zooplankton), then uses its claws to eat the animal, forming a hollow in its body. It then enters the barrel-like, hollow body of its prey and travels the waters using it as a vehicle. In the same gelatinous barrel, the females lay their eggs and nourish their larvae. The structure of the barrel enables the parasite to be more buoyant in the water. The characteristics of Phronima is not completely known as it needs to studied alive and that is very difficult. Many of the aspects of Phronima’s life remain a mystery to science. (source)

4. Spinochordodes tellinii is a parasitic worm that develops in grasshoppers which, when fully grown, makes the grasshopper jump into the water, causing it to drown.

Spinochordodes tellinii (S. tellinii) is one vindictive parasite. This parasitic worm that can grow into a size that is three to four times longer than the host grasshopper, enter their host’s body in the form of larvae through the intake of food. Eventually, taking nourishment from the grasshoppers and crickets, they grow strong enough to control their behavior. It influences the grasshopper to jump into a water body where it can easily drown. It does this so that it can leave the body of the grasshopper and reproduce in the water. The parasite does not influence the grasshopper to actively seek water but does so only when it near to a water body. It was revealed in a study in 2015 that the infected grasshoppers create different proteins in their brains than the uninfected ones which are directly a result of the infection by S. tellinii. (source)

5. Naegleria fowleri is a freshwater parasite that can enter the human brain through the nasal cavity while swimming in freshwater lakes or poorly sanitized pools. The parasite destroys human brain tissue and has a fatality rate of 97%.

Image credits: cdc.gov

Known as the “brain-eating amoeba,” Naegleria fowleri is an organism that will make you think twice before you jump into a water body to swim next time. Found in warm, freshwater lakes and rivers and in poorly sanitized pools, the parasite targets children and teenagers. Once infected, the chances of survival are only 3%. It causes a swelling in the brain called “primary meningoencephalitis,” and within days, a person can die. However, infection from this parasite is rare and in some cases, can be treated. Only 34 cases were reported in the United States from 2004-2014. Scientists are concerned that climate change could help this parasite thrive as it needs warm water bodies.

Naegleria fowleri can only enter the human body when the water enters inside the nasal cavity. It burrows into the olfactory nerve that leads directly to the brain. Using its suction-cup like structures, it feeds on the brain tissue giving rise to the very first symptoms of infection—a loss of smell and taste. As the infection progresses, it can cause hallucinations, seizures, and confusion. As the body fights against the infection, it causes inflammation and extreme pressure on the skull which pushes the brain downwards severing the connection with the spinal cord causing death. Using nose plugs and not immersing the head under the water can help in preventing the infection. (source)

6. Acanthocephala is a parasite that causes some animals to lead themselves to their death because a parasite is “brain-jacking” them. Acanthocephala is one such parasite which infects crustaceans and forces them to swim to the water’s surface so they’re eaten by ducks.

Image credits: Omar Mohamed Amin, Richard Anderson Heckmann and Nguyen Van Ha via wikipedia, Ferran Pestaña/flickr

Also known as “thorny-headed worms,” Acanthocephala has spines through which they pierce and hold the gut wall of their host. Their life-cycles are very complex and involve at least two hosts who could be mammals, fishes, birds, or amphibians. They begin their life-cycle by occupying vertebrates who live in marine or freshwater bodies. A small crustacean, Gammarus lacustris, is often preyed upon by the parasite. The crustacean’s innate nature is to avoid light and remain in the depths of the water to avoid being preyed upon by ducks. But once infected, the parasite influences the crustacean’s behavior making it swim on the surface by attracting it to light. It can also make the crustacean latch itself on a rock or plant so that ducks can spot it and eat it. For the Acanthocephala to thrive, it is necessary for the duck (second host) to eat its first host.


Their life cycle goes like this… the host excretes the parasite’s egg through its feces which is then ingested by a crustacean or another arthropod. It develops when in the body of the intermediate host and grows mature and mates in the body of its final host. The process then repeats. There have been a few cases of human infections but they are treatable. (source)

7. Pleistophora mulleri is a parasite that makes shrimp consume much more of their own kind drastically increasing their cannibalism and making them take much less time to consume their prey.

Image credits: University of Leeds/eurekalert

Parasites can be ruthless and Pleistophora mulleri is an example of that. It can make the indigenous shrimp Gammarus duebeni celticus consume its own kind much more than its usual eating patterns. Researchers have found that the parasite drastically increases the indigenous shrimp’s cannibal-like traits and also makes them more voracious leading them to consume their prey in a far shorter time than the uninfected ones.

The parasite relies on the host for food, and millions of them latch themselves in the host’s body. It is because of the increased demand for food that the shrimp become more voracious and cannibalistic. The Irish waterways have seen the shrimp species Gammarus duebeni celticus replaced by the invasive species Gammarus pulex. Researchers have stated that the parasite is responsible for the weakening the resistance of the former. (source)

8. Nycteribiidae and Streblidae are two families of the species of horrifying parasites which are flies that attach themselves to a bat’s head and suck its blood.

Image credits: Gilles San Martin/flickr

If you thought bats were horrifying, wait until you hear about the bat flies. About 275 species in the Nycteribiidae family and 225 in the Streblidae family suck bat blood. The bat flies belonging to the Nycterbiidae family are wingless and have a spider-like appearance, while the ones in the Streblidae family have functional wings. These bat flies who have evolved over millions of years spend their entire life cycle clinging to the bodies of bats, particularly to their fur and wings. Researchers believe that 20 million years ago before these flies evolved, they would have consumed bat’s sweat, feces, and dead skin. Two days after being separated from their host bat, the bat flies die. (1,2)

9. Ribeiroia ondatrae is one of the most horrible parasites on the planet. It forces frogs to have several defects like multiple legs that jut out at weird angles to affect their mobility to put them in danger of predators.

Image credits: Brett A. Goodman, Pieter T. J. Johnson/journals

A flatworm parasite, Ribeiroia ondatrae, infects frogs when they are still developing their limbs. It leads to several defects in the amphibians like no legs or multiple legs that pop out at weird places in the body. This makes it difficult for the frogs to move and makes it easy for the predators to feast upon them leading to an early death. This parasite, which is a grave threat because it is constantly moving, can also land in an area where endangered or threatened species form a habitat. Scientists have been trying to predict the places where these malformation-causing parasites could exist to prevent further harm to the animals.

The life-cycle of this parasite begins with a ramshorn snail where it asexually clones itself, converting the snail into a “parasite machine” of a kind. Hundreds of parasites are released by the snail every night looking for their second hosts, the tadpoles. The tadpoles grow up to become a frog with defects which are quickly eaten by birds. The birds are the third host. The parasite reproduces inside the birds, the eggs are released to the feces of the birds, and the cycle repeats. (source)

10. Diplostomum pseudospathaceum is a parasite that lives inside the eyeball of a fish and controls its behavior. When young, the parasite protects the fish. When it grows, it leaves no stone unturned to get the fish eaten by birds.

Image credits: Ron Caswell/flickr, dailyparasite

Imagine a parasite pulling the strings from inside the eyes of a fish! Diplostomum pseudospathaceum is a parasite that changes its host’s behavior to fit its needs. Beginning their life cycle with a snail, the parasite then finds its way into the eyeball of a fish by penetrating the skin of the fish in the water and hiding out until maturity. When young, it protects the fish so that it can grow, but once it is mature, it will do all it can to get the fish eaten by a bird so that its life cycle can continue inside the bird’s body. The parasite mates in the bird’s digestive tract and its eggs are released through its feces like many other parasites. In a 2015 study, it was revealed that fish infected with the immature parasite swam slower than the uninfected ones making them less visible to prey. It was also found that the fish that were infected with the mature parasite swam much more actively than the uninfected ones. (source)


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