6 Horrifying Parasites

By Chris Connolly

These life-sucking go-getters have managed to carve out some of the most ingenious survival strategies in the world. By some estimates, parasites outnumber free-living species nearly four to one. So show some respect. After all, mooching isn't as easy as it looks.

1. Cymothoa exigua: Biting Your Tongue, So You Don't Have To

When fish mommies want to strike fear in the hearts of their misbehaving fish babies, we suspect they draw on the chilling animal savagery of the Cymothoa exigua. As a youngster, this nasty little parasitic crustacean begins a life of terror by fighting its way through the gills of its fish host of choice, the snapper. Once there, it attaches itself to the fish's tongue and begins feeding on the rich blood pumping through the artery underneath. As the parasite grows, it drinks more blood and eventually causes the tongue to atrophy and disintegrate. But does the Cymothoa mouth-squatter leave its fishy friend tongueless? Of course not. It does what any crafty parasite would do and replaces the old tongue with its own body. The fish is actually able to use the parasite just like a normal tongue, only it has to share all the food with its new friend. Yes, the whole foster-tongue thing seems like a pretty nice gesture on the part of ol' Cymothoa—until you remember there was nothing wrong with the fish's old tongue in the first place.

2. Screwworms: Causing Problems Right out of the Hatch

Plenty more (disgusting) creatures after the jump...

worms.jpgThe screwworm isn't really a worm at all; it's a type of fly. But if living under a false name were the worst of the screwworm's misdeeds, you can be sure it wouldn't appear in this story. No, this parasite's rap sheet is about to get much, much more disturbing. To find its host, an adult female screwworm seeks out exposed flesh on an animal (usually some sort of livestock, but an injured soldier or a human baby isn't out of the question) in search of a place to lay her eggs. She prefers wounds, but may also settle on using the eyes, nostrils, or anus of her victim to construct a nursery. Next, the 200-or-so eggs hatch, and the larvae start burrowing into their host's flesh. Once they're situated in their cozy little meat tunnels, the infant flies continue to feed and grow. The bigger they get, the more they have to eat. Eventually, this creates a whole lot of festering and oozing on the host, which attracts more flies, which lay more eggs, which do more feeding and burrowing. It's a brutal onslaught, and a swift one. Screwworm larvae are reportedly capable of consuming an entire sheep or dog from the inside out in five to seven days.

3. Sacculina carcini: Reasons You Shouldn't Pick up a Hitchhiker

Sacculinacarciniweb.jpgIf you ever have a choice between being possessed by the devil and being possessed by a Sacculina carcini, opt for the devil—no contest. A female sacculina begins life as a tiny free-floating slug in the sea, drifting around until she encounters a crab. When that fateful day arrives, she finds a chink in the crab's armor (usually an elbow or leg joint) and thrusts a kind of hollow dagger into its body. After that, she (how to put this?) "injects" herself into the crab, sluicing through the dagger and leaving behind a husk. Once inside, the jellylike sacculina starts to take over. She grows "roots" that extend to every part of the crab's body—wrapping around its eyestalks and deep into its legs and arms. The female feeds and grows until eventually she pops out the top of the crab, and from this knobby protrusion, she will steer the Good Ship Unlucky Crab for the rest of their commingled life. Packed full of parasite, the crab will forgo its own needs to serve those of its master. It won't molt, grow reproductive organs, or attempt to reproduce. It won't even regrow appendages, as healthy crabs can. Rather than waste the nutrients on itself, a host crab will hobble along and continue to look for food with which to feed its parasite master.

4. Filarial Worms: Proof You Need Thicker Skin

lf2.jpgFilarial worms are the nasty little suckers you can thank for lymphatic filariasis, which, according to the Pacific Program to Eliminate Lymphatic Filariasis, is the second-leading cause of permanent and long-term disability in the world. (Mental illness is No. 1.) Filarial worms are round, thread-like parasites that travel from human to human via that harbinger of disease transmission, the mosquito. How do they make the leap of host? In an interesting (if scary) example of parasite ingenuity, filarial worm embryos living underneath the skin can sense the onset of night, which is their cue to head upward to the skin's surface in order to increase their chances of being picked up by a passing 'skeeter. Should they get sucked up, they grow into larvae within the mosquito's muscle fibers and then get themselves injected into new hosts. Once they've returned to a human home, they open up a franchise in the family business—Wreaking Havoc. Filaria often lodge in the body's lymphatic system, where they can inflict any number of torturous symptoms, not the least of which involves carting your genitals off to the elephantiasis clinic in a wheelbarrow.

5. Guinea Worms: Exposing Parts Nobody Wants to See

guinea-worm.jpgWhere there are guinea worms, there is Guinea Worm Disease—and that's usually in Africa. When a human consumes water contaminated with guinea worms, the little buggers infiltrate their host's intestinal walls and commence mating. After conception, the males die off, and the females hang around for about a year, growing and eating. Eventually, these slender ladies get bored and decide they need to lay some eggs. To do so, they make their way down the body to the lower extremities, where they bore a small hole through the skin. The resulting lesion begins to fester and burn, which usually leads the host to plunge his or her foot into a soothing bucket of water. (Of course, in areas where an entire village shares a single water source, this helps spread the infection.) Unfortunately for the sufferer, the water doesn't solve the problem of having a three-foot female worm dangling its genitalia out of your foot. And to complicate matters, if you yank on that sucker, it'll break apart and could cause a fatal infection. So how do you rid yourself of the not-so-little hitchhiker? You go see a doctor, who—over the course of three or four weeks—will kindly wind the worm around a stick, inch by agonizing inch. Not the most pleasant method, but certainly a proven one. This cure for a guinea worm infection has been around so long, some believe it's where we get the snakes-around-a-staff symbol for medicine.

6. Leucochloridium paradoxum: Parasite for Sore Eyes

mimicry_2.jpgPrepare to be dazzled. This parasite's got a life cycle more mind-bending and chilling than an M. Night Shyamalan film. Leucochloridium paradoxum are a type of fluke (a.k.a., parasitic flatworm) that prey on birds—a fascinating turn of events considering they begin their lives as eggs in bird droppings. Thus, the problem facing baby Leucochloridium paradoxum is, "How do I get myself back into one of those feathery things?" Taking a page from Greek history, the infant flatworms rely on Trojan trickery. First, they hang out in the droppings until a snail happens along and eats the bird dung. Then they initiate their devious plan of action by taking up residence in the snail's eyestalks. (Sure, it sounds slimy and gross to us, but after a childhood spent living in bird feces, it's a step up.) As they mature, the flukes become visible through the snail's translucent skin. And that's when things really get interesting. To a bird, this fluke-filled eyestalk looks like a caterpillar. So the bird devours the stalk and ends up with a bellyful of Leucochloridium paradoxum that will, of course, lay eggs and begin the cycle again. Meanwhile, the snail shakes its head, shops for an eye patch, and vows never to eat feces again.

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Ed. note: We thought the parasites were so horrifying that we decided to get the very talented Randy Riggs to film a B-horror movie around the subject. Here's the trailer for what he came up with.

This article was pulled from an earlier edition of mental_floss. Make our editors happy and subscribe today.

Celebrate the Holidays With the 2020 Harry Potter Funko Pop Advent Calendar

Funko
Funko

Though the main book series and movie franchise are long over, the Wizarding World of Harry Potter remains in the spotlight as one of the most popular properties in pop-culture. The folks at Funko definitely know this, and every year the company releases a new Advent calendar based on the popular series so fans can count down to the holidays with their favorite characters.

SIGN UP TODAY: Get exclusive deals, product news, reviews and more with the Mental Floss Smart Shopping Newsletter!

Right now, you can pre-order the 2020 edition of Funko's popular Harry Potter Advent calendar, and if you do it through Amazon, you'll even get it on sale for 33 percent off, bringing the price down from $60 to just $40.

Funko Pop!/Amazon

Over the course of the holiday season, the Advent calendar allows you to count down the days until Christmas, starting on December 1, by opening one of the tiny, numbered doors on the appropriate day. Each door is filled with a surprise Pocket Pop! figurine—but outside of the trio of Harry, Hermione, and Ron, the company isn't revealing who you'll be getting just yet.

Calendars will start shipping on October 15, but if you want a head start, go to Amazon to pre-order yours at a discount.

This article contains affiliate links to products selected by our editors. Mental Floss may receive a commission for purchases made through these links.

12 Fascinating Facts About Crows

Mick Thompson, Flickr // CC BY-NC 2.0
Mick Thompson, Flickr // CC BY-NC 2.0

Crows often get a bad rap. In many Western cultures, they've historically been associated with death, disease, and bad omens; reviled as crop-stealers by farmers, and condemned as nuisances by city dwellers. But the birds are fascinating creatures, adaptable and brainy to an extent that's almost scary. Here are a few facts about these crafty corvids that might surprise you.

1. All crows and ravens belong to the same genus.

Members of the genus Corvus can be found on every continent except Antarctica and South America (although other close relatives live there). To date, scientists have named 40 species. Colloquially, some of them are referred to as ravens while others are called crows, rooks, or jackdaws.

Historically, the name raven has been given to several of the big-bodied Corvus birds with shaggy feathers on their necks. Mid-sized members of the genus are usually called crows, while the very smallest species go by the name jackdaws. There's also a large-beaked outlier known as the rook, which was named after the unusual sound it makes. But pervasive as these labels may be, they're not scientific and do not reflect the latest research. Despite its informal name, the so-called Australian raven is more closely akin to the Torresian crow than it is to the common raven.

In the U.S., when people talk about crows and ravens, they're usually referring to the American crow (Corvus brachyrhynchos) and the common raven (Corvus corax). Telling them apart can be tough, but it is possible for eagle-eyed birders. One big indicator is size: The common raven is much larger, about the size of a red-tailed hawk. It also has a more wedge-shaped tail. As Kevin J. McGowan of the Cornell Lab of Ornithology writes on his crow FAQ page, ravens soar longer than crows, and you can see through their wing feathers as they fly (among other differences). And the birds' calls are substantially different. "American crows make the familiar caw-caw, but also have a large repertoire of rattles, clicks, and even clear bell-like notes," McGowan writes, whereas common ravens have "a deep, reverberating croaking or gronk-gronk. Only occasionally will a raven make a call similar to a crow's caw, but even then it is so deep as to be fairly easily distinguished from a real crow."

You can hear crow vocalizations here and raven vocalizations here.

2. Older crow siblings can help their parents raise newborn chicks.

Like a lot of intelligent animals, most crows are quite social. For instance, American crows spend most of the year living in pairs (they usually mate for life) or small family groups. During the winter months, they'll congregate with hundreds or even thousands of their peers to sleep together at night in a sprawling communal unit called a roost.

Come nesting season, a mated pair of crows might be lucky enough to receive chick-rearing help. Juvenile birds are frequently seen defending their parents' nest from predators. Other services they can provide include bringing food to mom and dad, or feeding their younger siblings directly. One study found that 80 percent of American crow nests surveyed had a helping hand. And some birds become regular nest assistants, providing aid to their parents for over half a decade.

3. When a crow dies, its neighbors may have a funeral.

The sight of a dead crow tends to attract a mob of a hundred or more live ones. During this ritual, the live crows almost never touch the dead one, which rules scavenging out as a motive. Why do they do this? Some studies suggest that the mass gathering is part of a survival strategy: The birds are learning about threats and seem hesitant to revisit any spot where they've encountered a dead crow, even if food is plentiful there.

4. Crows have caused blackouts in Japan.

Since the 1990s, crows have experienced a population boom in Japan, where—not coincidentally—delicious garbage is more plentiful than ever before. This is bad news for power companies. Urban crows like to nest on electric transformers and will often use wire hangers or fiber-optic cables as building materials for their nests. The result was an epidemic of crow-caused blackouts in major cities around Japan: Between 2006 and 2008, the corvids stole almost 1400 fiber-optic cables from Tokyo power providers, and according to the Chubu electric company, crows are responsible for around 100 power failures per year in their facilities alone.

To fight back, Chubu started installing artificial "love nests" in 2004. Made with non-conductive resin, the nests are placed on company towers high above the power lines, where the birds are unlikely to cause any trouble. The strategy seems to be working: 67 percent of the faux nests are currently in use, making life a lot easier for Chubu employees.

5. Proportionally, some crows' brains are bigger than yours. 

According to McGowan, crows are "smarter than many undergraduates, but probably not as smart as ravens."

Crows are so smart and so good at improvising that some zoologists admiringly call them "feathered apes." And yet, from a primate's perspective, crow brains might look puny. The New Caledonian crow, for example, has a brain that weighs just 0.26 ounces. But relative to its body size, that brain is huge, accounting for 2.7 percent of the bird's overall weight. By comparison, an adult human's three-pound brain represents 1.9 percent of their body weight.

Of all the living birds, crows, ravens, and parrots have the biggest brain-to-body size ratios. And in lab experiments, these avians show a degree of cognition that puts them on par with the great apes. In fact, research has shown that they have a much higher density of neurons in their forebrains than primates do. The amount of neurons in this region is thought to correlate with a given animal's intelligence. Theoretically, having more neurons translates to better cognitive reasoning.

A 2020 study looked at whether crows, like humans and great apes, can demonstrate consciousness. Crow brains lack a cerebral cortex, where most of the primate brain's conscious perception happens. Researchers tracked the brain activity in two crows as they performed different tasks, and discovered that they could perceive sensory input—suggesting that there is much more to understand about the evolution of consciousness.

6. Crows have regional dialects.

Apart from the famous caw, caw noise, crows emit a number of other sounds. Each one sends out a different message; for example, cawing can be used as a territorial warning or a way for crows to signal their location to relatives.

This avian language isn't homogeneous; two different populations of crows may have slight differences. As ornithologist John M. Marzluff and author Tony Angell noted in their 2005 book In the Company of Crows and Ravens, the calls these birds use "vary regionally, like human dialects that can vary from valley to valley." If a crow changes its social group, the bird will try to fit in by talking like the popular guys. "When crows join a new flock," Marzluff and Angell wrote, "they learn the flock's dialect by mimicking the calls of dominant flock members."

7. Some crows can read traffic lights.

In Japan, carrion crows (Corvus corone) use cars like oversized nutcrackers. The birds have learned to take walnuts—a favorite treat—over to road intersections, where they put the hard-shelled snacks down onto the pavement. The crow then waits for a passing vehicle to smash the nut, after which it will swoop down and eat the delicious interior.

It's a risky trick, but the crows aren't usually run over because (unlike some people) they've figured out what traffic lights mean. Carrion crows wait until the light turns red before flying down to place the un-cracked nut on the road. The second the light goes green, the crow takes off to watch the nut get run over from afar; it will even wait for the next red to scoop up the nut's insides.

This behavior isn't limited to just one corvid species: American crows have been observed doing the same thing in California.

8. Crows can recognize your face—and hold a grudge.

You don't want a crow for an enemy. In 2011, a team from the University of Washington published a remarkable study about the brainpower of local crows. The researchers' goal was to figure out how well the birds could identify human faces. So—in the name of science—they went out and bought two Halloween masks: One resembled a caveman, the other looked like Dick Cheney. It was decided that the caveman getup would be used to threaten the birds, while the Cheney mask was relegated to control status.

At the five sites, a scientist donned the caveman mask before catching and banding some wild crows. Getting trapped is never a fun experience, and upon their release, the ex-captives loudly "scolded" their assailant with a threatening caw. Seeing this, other birds who had been sitting nearby joined in the fray, swooping down to harass the neanderthalic visitor. Over a period of several years, both masks were regularly worn by team members on strolls through all five test spots. Without fail, the caveman mask was greeted by angry scolds and dive-bomb attacks from crows—including many who'd never been captured or banded—while the birds largely ignored the Dick Cheney mask.

Amazingly, the caveman disguise continued to provoke a hostile response five years into the experiment—even though the team had stopped trapping crows after those first few site visits. And some of the birds who antagonized the mask-wearer weren't even alive back when the whole thing started. The younger crows couldn't possibly have seen the imitation caveman grab an acquaintance of theirs—but they scolded it anyway. Clearly, the grudge had been passed on; birds were still attacking the mask as recently as 2013.

The moral of this story? Mind your manners around crows. Because if you mistreat them, they won't forget you and neither will their friends—or the next generation.

9. New Caledonian crows make and use tools.

Lots of non-human animals, including chimpanzees and orangutans, create useful implements which help them survive in the wild. The New Caledonian crow (Corvus moneduloides) is one of only two species on the planet that can craft its own hooks in the wild. The other is called Homo sapiens. The South Pacific avian uses the hooks—which are made from pliable twigs that the crows bend using their beaks and feet into a J-shape—to extract insects from tight crevices.

Another surprising attribute is this species' bill. Unlike virtually all other birds, the New Caledonian crow has a bill that does not curve downwards. For years, the quirk went unexplained, but scientists now think that the avian's unique beak evolved to help it grasp tools more easily, as well as to better see what the tool is doing.

The New Caledonian crow isn't the only implement expert in the corvid family. In 2016, scientists at the University of St. Andrews demonstrated that the ultra-rare Hawaiian crow, or ‘Alalā (Corvus hawaiiensis), is similarly adept at using and modifying tools.

10. Crows fight off predators by ganging up on them.

Crows have to deal with a menagerie of predators, such as hawks, owls, coyotes, and raccoons. To ward them off, the corvids exploit the fact that there can be strength in numbers. Upon seeing a would-be attacker, crows are known to gather, with some groups consisting of a dozen birds or more. Individual crows then swoop down to deliver passing blows with their beaks, often inflicting serious bodily injury in the process. If all goes well, the target will back off—though it may kill a few of the dive-bombers before they retreat. Corvids are by no means the only avians that mob would-be attackers. Swallows, chickadees, and even hummingbirds have all been documented doing this. In fact, crows are sometimes at the receiving end of mob violence as smaller songbirds often feel threatened by them and lash out collectively.

11. Crows understand a thing or two about impulse control.

A 2014 study shows that at least some corvids can resist the urge for instant gratification—if you make it worth their while. The research was led by University of Göttingen graduate student Friederike Hillemann, whose team assembled five common ravens and seven carrion crows. Through careful note-taking, the scientists figured out what the favorite meal items of all 12 animals were. Then the experiment began.

With an outstretched hand, one of the researchers gave each of their birds a morsel of food. Then, the animals were shown a different piece of grub. The corvids were made to understand that if they liked the second option better, they could swap snacks—but only if they were willing to sit patiently for a certain period of time first. If a bird ate the original treat during that stretch, it forfeited the chance to trade it for a new one.

Hillemann's results showed that the crows and ravens didn't mind waiting around for an improved snack option. As such, a bird with a piece of bread was content to sit quietly if it knew that some fried pork fat would eventually be gained in the trade-off. However, if that same bird's second choice was another piece of bread, sitting tight would be pointless. So understandably, corvids who were put in this kind of situation tended to go ahead and eat whatever they'd been given. Why wait for more of the same?

12. YOU CAN CALL A GROUP OF CROWS A MURDER, BUT SOME SCIENTISTS WOULD RATHER YOU DIDN'T.

According to the Oxford English Dictionary (OED), the correct term for a group of crows is a murder, an expression bird-watchers and poets have been using since at least the 15th century, which the OED speculates may allude "to the crow's traditional association with violent death, or … to its harsh and raucous cry." But maybe it's time to come up with a replacement. McGowan hates the phrase "murder of crows." To him, it only feeds the public's negative outlook on the animals. "These birds aren't a gang of nasty villains," he wrote in the book Birdology. "These birds are just birds." McGowan would also have you know that American crows rank among "the most family-oriented birds in the world."