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The 10 Most Horrifying Parasites in the World


Two species can interact with one another in a wide range of ways. Out of those, parasitism is one of the nastiest. After all, it features one species that is specifically adapted for living inside another species while causing the latter harm, which is the stuff of nightmares. For proof, look no further than the parasites that can be found in fiction, with an excellent example being the Chestbursters from the Alien franchise. Unfortunately, nature can be much more inventive than the human imagination, meaning that there are worse parasites that can be found out there.

Ampulex compressa

There are some extremely unpleasant wasps that can be found out there. To name an example, consider the zombie wasp, which is one of the wasps that lays its eggs in its victims. To be exact, it will use its stinger to disable a cockroach's escape instinct, lead the cockroach to its nest, lay an egg in the cockroach, and then seal in the cockroach. Eventually, a larva will emerge from the egg, feed to its heart's content, and then use the resulting carcass as a cocoon until it emerges as a full-grown adult.

Cochliomyia hominivorax

Chances are good that people who recognize Latin will be less than enthused by this particular parasite. After all, hominivorax means exactly what it sounds like, which is to say, "man-eating." As for why this parasite is called "man-eating," the gist of it is that it is a fly that lays its eggs in open wounds. Each fly lays about 100 eggs, so when the latter hatch, the host experiences the extremely unpleasant sensation of about 100 maggots burrowing through their flesh while eating the entire time. On top of that, they respond to attempts to remove them by burrowing even deeper, which is exactly as pleasant as its sounds.


The concept of zombies aren't that far-fetched. After all, cordyceps fungi are a thing. For those who are unfamiliar, these will infect their host, control their host's behavior, and eventually burst out of their host's head. As a result, it is no wonder that The Last of Us explained its zombie outbreak using cordyceps fungi.

Cymothoa exigua

Chances are good that interested individuals have seen pictures of this parasite at some point. After all, pictures of the tongue-eating sea louse has been spread around a lot on the Internet. As for what it does, well, it is exactly what it sounds like. A tongue-eating sea louse feeds on the blood of a fish's tongue until the latter just withers away. Once that happens, it will replace the tongue so that it can continue feeding.


As strange as it sounds, this parasite is horrific because of its length. People can get this by drinking contaminated water. Unfortunately, they will become aware of this parasite's presence when it emerges through their skin, with the legs and the feet being the most common locations of the emergence. Even if people don't see it, they will notice it because of the burning pain. Moreover, there is no way to remove it other than to gradually pull it out with the help of a stick over the course of days.


Filarial worms are parasites that target vertebrates. However, they are very specialized, meaning that the number of species that are specifically well-adapted for humans is relatively low. Still, filarial worms are responsible for a lot of human misery, as shown by the estimate that more than 120 million people are infected in the modern world. To name a potential consequence, filarial worms can cause elephantiasis, which is when parts of the human body swell up and harden because of the obstruction of the lymphatic vessels.

Leucochloridium paradoxum

This is a species of flatworm that has sometimes been called the eye-inflating flatwarm. This is because when a snail consumes its eggs, their eye-stalks will become swollen with its larvae before proceeding to wriggle as though caterpillars. For humans, this is a remarkably disgusting sight. For birds, this is a tempting target. On top of this, this flatworm can exert influence over its host as well. Infected snails are likelier to head out into the open, thus making them likelier to be picked off. Even worse, their eyestalks can regenerate, meaning that they will be subjected to attack after attack until they have played their role in continuing the flatworm's life cycle.

Loa loa

It should be mentioned that this is one of the filarial worms. However, it gets its own paragraph because, well, it's called the eye worm. In short, people can get this parasite through fly bites. After which, it can make its way to the human eye, where it can be felt by the host as well as seen by other humans. This is actually good because this makes it possible to extract the eye worm. In contrast, well, suffice to say that the eye worm has been known to cause brain damage.

Toxoplasma gondii

As mentioned earlier, some parasites can affect their host's behavior. To name another example, there is Toxoplasma gondii, which gets a lot of attention because of a couple of reasons. One, it is known to make rodents more willing to accept risk, thus increasing the chances of them being eaten by cats. Two, it is very easy for humans to get this parasite by coming into contact with raw meat, unwashed vegetables, and surfaces that have come into contact with infected cat poop. It isn't quite clear how this parasite affects humans, but there are studies that suggest that infected humans are likelier to get into car accidents.

Vandellia cirrhosa

This species is sometimes called by the oh-so-lovely name of vampire fish. This is because they are blood-suckers that tend to parasitize the gills of other fish in the Amazon Basin. However, vampire fish are much better-known because of the claims of them parasitizing humans. Fortunately, the story of them swimming up a stream of urine to enter a human urethra is false. Unfortunately, there is a recorded incident of them entering a man's urethra. Furthermore, there are recorded incidents of them entering a woman's vaginal canal. Bear in mind that vampire fish possess backward-facing spines, which are what enable them to lodge themselves in their victims.

Dana Hanson

Written by Dana Hanson

Dana has extensive professional writing experience including technical and report writing, informational articles, persuasive articles, contrast and comparison, grant applications, and advertisement. She also enjoys creative writing, content writing on nearly any topic (particularly business and lifestyle), because as a lifelong learner, she loves to do research and possess a high skill level in this area. Her academic degrees include AA social Sci/BA English/MEd Adult Ed & Community & Human Resource Development and ABD in PhD studies in Indust & Org Psychology.

Read more posts by Dana Hanson

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