Aaron: Hi, I'm Aaron Carroll, the host of Healthcare Triage. Over on our show, we're doing a month-long run on parasites that affect humans. The research for that show has pretty much ruined sleep for me. It's taking every bit of willpower I have not to scratch my head right now. We thought we'd share some of the pain with you, so fair warning, if insects or other creepy crawly things make you squeamish, you might wanna watch something else. Still with us?  Into the breach!

1) Did you know that bedbugs reproduce by traumatic insemination? After all, why use a female genital tract for its intended purpose, when you have a sharp, penis-like thing that you can stab into a female's abdomen and just ejaculate there? It leaves the females with a gaping wound, which can get infected and leave them more likely to die, but who cares? Not the male bedbugs, evidently. 

Get ready to fear everything, 'cause that's the first of many fascinating, and sometimes horrifying, things I'm gonna tell you about parasites today.

(mental_floss intro plays)

2) Malaria is caused by the parasite Plasmodium. What's mind blowing about this parasite is just how ridiculously deadly it is. The WHO has reported that malaria may have killed close to 200,000 million people in the 19th century alone. It still kills about 1.2 million people a year, and most of those are kids in Africa. There are experts who argue that malaria has killed about half of all human beings who have ever lived. Really. Regardless, malaria kills way more people than almost any other infection, and yet we freak out over things that are far, far less deadly way more often. Malaria's Plasmodium isn't the only horrible parasite that mosquitoes gift us with.

3) There's also the Wuchereria bancrofti, a roundworm that causes filariasis. Once they get into your body, they first set up shop in your blood vessels. They're most commonly found in vessels in your peripheral circulation, which is sort of the outside, as opposed to deep in your body, from about 10pm to 4am, meaning that they're making some sort of decisions on where to hang out in your body at different times of the day. Scientists think this is adaptive behavior to make them more likely to get into new mosquitoes who might bite you at the periphery at night. Later in their lives, they move into your lymphatic system, where they grow and eventually block it up. Then you get lymphedema and eventually elephantiasis, which most commonly affects the arms, legs, breasts, and scrotum, 'cause why wouldn't it? 

4) There are other horrifying roundworms that cause filariasis. Take the loa loa worm. The larva develop in horseflies which can bite people and infect them. Then, the larva travel through our subcutaneous tissues. At some point, they stop and start to develop into adults. If you're lucky, that'll be in your joints, where they cause swelling and inflammation. If you're unlucky, they get to your eye. If they do, they swim around in there, and you can feel them swimming in your eye. If they get big enough, you can even see them in your eye. And then can live inside you for about 17 years.

5) Tapeworms come in a number of varieties, but the ones that are more common in the United States come from beef. If you get one of these numbers, they can grow inside you to about 30 feet in length. The idea of a 30 foot worm is repulsive enough, but the thought of a 30 foot worm living in your belly is almost incomprehensible. Even if you get it treated, can you imagine passing that into the toilet? Can you? 

6) There's a flatworm of the genus Ribeiroia that infects amphibians while they're tadpoles. Once it gets in there, it likes to head to the part of the tadpole that eventually becomes legs. Then it makes everything go wrong. Frogs infected with these larvae grow extra legs that are tangled, weird looking, and monstrous, and when frogs like this are discovered, we often fear that they're living near radiation or toxins, but once again, parasites.

7) Entamoeba histolytica is a single-cell organism that can infect you for years. You usually get it from dirty water or unwashed food. Most times, they stay in your gut and cause local disease, but sometimes they get out and invade other tissues, causing abscesses, or pockets of infection. At the 1933 Chicago Worlds Fair, there was an outbreak from contaminated drinking water that infected about 1,000 people and killed 58 of them from amoebas, single-cell organisms.

8) Although not a true amoeba, Naegleria fowleri made news a couple years ago because it killed a couple people in the United States. How? Ready for this? Neti pots. Yes, those things that some people use to wash out their sinuses. Turns out two people in Louisiana used tap water, which contained these guys, and they used the opportunity of being in their sinuses to work their way to the brain and murder human beings. I've never understood the allure of neti pots to be honest, but the fact that they can let brain-eating single-celled organisms into your skull pretty much sealed the deal that I won't be using them.

9) Hookworms are the only worms that have teeth. Lucky them, unlucky you, 'cause they use these teeth to latch onto your gut, where they can spend up to 15 years feeding and reproducing, and I mean reproducing, 'cause the female hookworm can produce 20,000 eggs a day, for like 15 years. When you're infected, you can have thousands of these guys inside you. They can cause diarrhea, weight loss, difficulty breathing, and even mental retardation in kids from blood loss and lack of oxygen to the brain. Their Latin name is Necator americanus, which literally means 'American Murderer'.

10) Guinea worms prey only on humans. You get infected with them when you drink water that's infested with their larvae. They mate inside your GI tract, and then they start to grow. Eventually, female worms burrow their way out to the skin, where they create incredibly painful sores by which they can exit the body. They exit very slowly, causing a burning pain as they do. There's no treatment for guinea worms, there's no vaccine. The best we can do, even today, is to wrap the part of the worm that's exposed around a stick and slowly pull it out. That can take weeks and it's not pleasant at all. One of the only things that soothes the pain is to submerge the worm and the sore in water, which is, of course, exactly what you don't want to do, as it allows the worm to release its larvae and start the cycle all over again. But here's some good news: in 1986, about 3.5 million people were infected worldwide, but today, thanks to efforts spearheaded by the Carter Center, by April 30th of this year, there had been only three documented cases in the whole world. It's thought that we might eradicate this parasite from the face of the Earth soon, which is amazing.

11) Cymothoa exigua is insane. The parasite infects red snappers, the fish, by entering first through the gills. There, it works its way to the bottom of the fish's tongue, where it latches on and starts to feed. As it grows, it takes more and more away from the tongue, until the tongue withers away and falls off. At that point, it's about the size of the old tongue, so it latches on to the muscles in the fish's mouth in such a way that the snapper starts to use the parasite as if it were a tongue. They can also change gender, apparently, but that's not even interesting when you know the whole tongue thing.

12) Horsehair worms thankfully don't mess with humans, which is awesome, because they basically get their hosts to kill themselves. They mostly infect insects, like grasshoppers. As larva, they plant themselves on vegetation and form cysts for an unlucky grasshopper to eat.  Inside the insect, they do the usual thing of feasting and growing, right up until they wanna mate. They need water for that, so what do they do? They release some compound that makes the grasshopper want water so badly that it'll jump right in, even though grasshoppers can't swim. The unlucky hoppers drown, and as they do, the horsehair worms come pouring out of their anuses where they can mate and go about their happy lives.

13) Let's talk about the Emerald Jewel Wasp, otherwise known as the Emerald Cockroach Wasp. Why? 'Cause this wasp totally ruins a poor cockroache's life. When the female wasp is ready to reproduce, she finds an unsuspecting cockroach, lands on it, and stings it right in the thoracic nervous system, which paralyzes its front half. This allows the wasp to deliver a second surgical sting, right into the part of the brain which controls a cockroach's escape reflex, which basically turns it into a zombie. Then, the wasp eats half of the roach's antennas. Why? No one really knows. Maybe for sustenance, and then it leads the now-zombified roach back to its lair, by what remains of its antennas. When it arrives, it lays an egg on the roach, and leaves the burrow and seals it, with pebbles to both lock in the roach and keep other predators out. The roach just lays there, like a zombie, alive, while the larva hatches, eats its way inside, and then consumes the cockroach's organs in an order which keeps the roach alive as long as possible, so that the larva has time to form a cocoon in its body. When it's done developing, it exits the dead roach and goes about its horrible Emerald Jewel Wasp life. 

14) That's not the only zombifying parasite. The Dicrocoelium dendriticum is a fluke that goes through a host of animals. They start their lives in snails, which get infested with the larva. The snails are smart, though, they wall off the parasite in cysts and excrete them. But that's when things go south. Ants eat the cysts, which can contain hundreds of tiny little flukes, and most hang out and develop and do their usual thing, but one lucky fluke heads up to the ant's subesophageal ganglion, where it takes control of the ant's nervous system. Somehow, it knows to wait until it's nighttime, and then it forces the ant, by controlling its nervous system, to leave its home, climb up a blade of grass as high as possible, and then bite down as hard as it can so it's stuck there. Why at night? 'Cause evidently the sun and heat are harmful to the fluke. If the ant makes it 'til morning, the fluke will release its control and the ant scurries home. But it makes the ant do this every night, up the blade of grass, in the hope that eventually, a grazing animal, like a cow, will eat it. Then they infect that animal until they start their life cycle all over again. 

You made it the whole way  You rock. Thanks for watching mental_floss on YouTube, which is made with the help of all these people. If you haven't had enough parasite information, you can head on over to my channel, healthcare triage, links in the description down below. We talk about a lot more than just parasites. You can also catch me writing about much less horrifying stuff over at my blog, The Incidental Economist, or over at The Upshot at the New York Times, links also down below. If you have a topic for the list show that you'd like to see in the future, leave it in the comments. Try not to get infected by parasites. Don't forget to be awesome.