From crustaceans that take the place of tongues to fungi that turn bugs into giant mushrooms, the parasites on this list are both disgusting and dangerous.
While not every creepy crawler affects humans, they all have one thing in common: they do some terrible things to the hosts they infect.
Special thanks to parasite expert and writer of The Loom, Carl Zimmer for helping us out.
Toxoplasma gondii: the parasite that makes mice attracted to cats
Harmful to humans: Yes
T. gondii is a feline related parasite that is only able to reproduce inside cats and is commonly found in cat feces.
How does it get there you ask? When rats and mice are infected with T. gondii they actually become attracted to cats, specifically their smell, which is obviously supposed to trigger fear in the rodents. This effect is beneficial to the parasitic protozoa because cats easily kill the infected rodent and become the new host of T. gondii.
Humans don't become attracted to cats when infected, but we do contract taxoplasma from the parasite which can cause brain damage to fetuses. This is the reason pregnant women are advised to stay away from cat litter.
Perhaps scarier, new studies have shown that taxoplasma may be related to schizophrenia in humans.
Loa loa: the worm that lives in human eyes
Harmful to humans: Yes
Loa loa also known as the "eye worm" is a parasitic worm that lives within humans and other mammals' bodies specifically, as you might suspect, eyes.
L. loa is contracted from certain flies and after an infected fly bites its victim, the worm begins floating around tissue of the bitten host. The worm travels along the tissue, moving through the body until it stops and causes swelling and irritation in that spot.
The creepiest thing about L. loa is that if it gets up to your eye tissue, you can actually feel it moving around in your eye. It can also be seen flowing around in there if its big enough.
Luckily the worm is easily killed using antibiotics or extracted through relatively minor surgery.
And by the way, this worm can live inside a human for up to 17 years.
Vandellia Cirrhosa: the catfish that will swim into your penis and eat your insides
Harmful to humans: Yes
V. Cirrhosa, also known as the candiru or vampire fish, is scary not so much because it drinks your blood from inside you, but because of how it can get inside you.
Normally the Amazon's candiru, a type of catfish that is typically a few inches long, follows the smell of ammonia to larger fish, where it climbs into their gills. When there it shoots out its sharp spine, lodging itself in its host's gills where it proceeds to engorge on blood.
Here's the really scary part: when humans urinate we also excrete ammonia and there have been confirmed cases of the candiru swimming up a urine stream into the victim's penis. Once there it will drink your blood until you have the very invasive and very painful surgery to get it out.
Granted, this is very rare and more frequently the vampire fish will find other entry points to get inside you (that's comforting) where it will once again drink your blood.
See the rest of the story at Business Insider