Some Of The Most Awful Parasites In The World

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Justine Alford

Guest Author

1373 Some Of The Most Awful Parasites In The World
Andy Heyward, via Flickr. Cymothoa exigua parasite.

It turns out that there are some SERIOUSLY messed up parasites in our world. You all know how much we love disgusting things, so we thought we’d share a few examples of the vilest parasites we could think of. I suggest you don’t read this if you’re thinking of eating any time soon.

Tongue Eating Parasite


Don’t worry- before you throw up over yourself thinking about something eating your tongue, this is a parasite of fish not humans. Cymothoa exigua is a parasitic isopod that starts off its life as a male but can switch sex later on (organisms such as this are known as protandric hermaphrodites). The parasites enter a host fish through the gills and set up camp here to mature. A female then crawls out from the gills and secures herself onto the tongue of the fish. Here's the part where it gets seriously messed up.

She pierces the tongue and starts sucking blood from it as a source of nutrition, gradually increasing in size until she takes up a large proportion of the mouth. Although she doesn’t drain enough to kill the fish, she drinks so much that the tongue wastes away and falls off, leaving the parasite in its place as a pseudo-tongue. Incredibly, the fish is still alive and kicking, and the cheeky gatecrasher even pinches the food that the host is trying to eat.

Now, you might not think there’s much room for any funny business in here, but they find a way. A male will crawl up from the gills and mate with the female inside the fish’s mouth- ew. She then releases her babies which will go on to continue the cycle again. Grim.

Cymothoa exigua taking up almost the entire mouth of a poor fish. Image credit: Marco Vinci, via Wikimedia Commons. 


Guinea-Worm Disease

This horrifying disease is caused by a parasitic worm called Dracununculus medinensis. Larvae of the guinea worm are ingested by water fleas which can then be consumed by thirsty humans if they drink untreated water. The stomach acid then dissolves the fleas, releasing the larvae that then burrow their way through the intestinal wall. The worms will then mature in the body- the female can reach up to a whopping 80 cm’s in length. If infected with both, male and female will worm around the both and find each other to mate, resulting in the female carrying 3 million embryos. That’s all the male is good for, so he dies, poor little fella.

The female then slithers through subcutaneous tissues, causing immense pain, until she arrives at the foot. Here, she pierces the skin and leaves the victim with a painful blister. Because it burns so bad, the human dunks the foot in water to try and ease the pain, which is exactly what the worm wants. The female then pokes her head out and vomits embryos from her mouth into the water so that they can wriggle away and get chowed on again by some poor unsuspecting fleas. The poor human then needs to spend weeks slowly extracting the worm to avoid breaking it which could cause a serious immune reaction. Shudder. 

Guinea worm emerging from an infected person's foot. Image credit: Otis Historical Archives of “National Museum of Health & Medicine,”​ via Wikimedia Commons. 


Mind-Manipulating Fungi

So you’re a fungus that lives in a tropical forest that experiences fluctuating humidity and temperature, but you can only thrive within a specific range of these variables. What do you do? Parasitize an ant, turn it into a zombie and make it seek out your perfect environment, of course. Oh, and then kill it and grow a big fungal pole out of its head, just for good measure.

The fungal parasite Ophiocordyceps is a spectacular example of host manipulation. Numerous different species have been described which differ in their host choice and death location. O. unilateralis, for example, infects carpenter (Camponotus) ants. The fungus then manipulates the host so that it abandons its usual habitat and heads for the sheltered underside of a leaf with ideal conditions for the fungus to grow. Here, the ant bites down on the leaf, usually on a vein, performing what is known as a “death grip.” The ant then dies and the hyphae (tubular fungal structures) grow inside the host, eventually tearing through the back of the head, looking like something out of Game of Thrones. Spores are then released from the fungus into a small area below the leaf referred to as an “infectious killing field,” ready to start the process over again. Lovely.

O. unilateralis infected ant with hyphae growing out of the head. Image credit: David Hughes, Maj-Britt Pontoppidan, PLoS ONE​, via Wikimedia Commons. 


Suicidal Crickets

Horsehair worms, obviously named because of their resemblance to horse hair, are endoparasites of various arthropods including crabs and crickets. The larvae live in marine or freshwater environments and are often eaten by insects such as mosquitoes. Infected insects may then get gobbled up by hungry, unsuspecting crickets and the horrifying process starts.

They burrow through the gut and then settle into a nice cozy body cavity, growing to around a foot in length on average. Then something weird happens- the worm needs to get back in the water to complete its life cycle, so it makes the cricket go kamikaze. Normally crickets stay the heck away from water for fear of death, but infected hosts seek out water and cannonball into it, causing them to die. The worms then wriggle out in search of a mate, job’s a good’un.

Although it is not known how precisely these worms alter the behavior of the cricket, studies have shown that the worms produce large quantities of neurotransmitters when inside the host and also cause the host to produce more neurotransmitters. Somewhere along the line this causes the cricket to behave in an abnormal and suicidal manner, waving goodbye to terrestrial life in favor of an early watery grave.


Here's a video of a poor suicidal cricket and the horsehair worm emerging:



Parasitoid Wasps


The majority of wasp species are actually parasitoids, meaning that they steal the body of another organism and use it as a nursery for their hungry offspring that chomp through the poor host while it is still alive. As if wasps could get any worse?! Evil winged devils.

There are a few truly disgusting examples of parasitoid wasps, starting with Glypatapanteles wasps. Members of this genus lay up to 80 eggs into a live caterpillar that then hatch and snack on the poor unsuspecting host’s body. The larvae eat their way through the caterpillar’s skin and attach themselves to a nearby piece of foliage and form a cocoon. Then, in a bizarre twist, the caterpillar turns bodyguard. It ignores its daily leaf chomping duties entirely and stands guard over the pupae, violently swinging its head at incoming predators, knocking them away. How the parasites cause the caterpillars to turn into faithful guardians is unknown, but unparasitized caterpillars don’t perform this behavior.

The emerald cockroach wasp, or jewel wasp, also turns its host into a submissive zombie by injecting venom directly into its brain with a powerful sting aimed right at the head. It then drags the confused and paralyzed cockroach into a chamber and lays an egg on it. The larva eventually hatches and bores inside the host, eating its insides while it is initially still alive. After gobbling much of its organs the cockroach dies, which we’re not too sad about because they are also disgusting. But what a way to go.

Emerald cockroach wasp. Image credit: Sharadpunita, via Wikimedia Commons. 


Filarial Worms

Last, but certainly not least, the worm that can turn you into a real sight for sore eyes. Filarial nematodes get into human hosts via mosquitoes which eat microscopic early stage worms the size of a red blood cell. These then migrate to the lymphatic system, mature, and of course mate.

Here, they can cause inflammation of the lymph nodes (lymphadenitis) and lymphedema, or tissue swelling caused by lymph fluid retention. Those with repeat, chronic infection are threatened with experiencing the rather unpleasant and disfiguring manifestation of elephantiasis which involves dramatic and often debilitating swelling of a body part. Unfortunately for the men infected with these worms, their scrotum can also swell up. Seriously unlucky. 

Ouch. Elephantiasis caused by filariasis. Image credit: CDC, via Wikimedia Commons. 


Header image: Tongue-eating-louse on snapper, by Andy Hayward, used in accordance with CC BY-NC-SA 2.0


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  • parasites,

  • cymothoa exigua,

  • guinea worm,

  • jewel wasp,

  • elephantiasis,

  • filariasis