10 Body-Snatching Parasites

Hans Hillewaert, Wikimedia Commons // CC BY-SA 4.03
Hans Hillewaert, Wikimedia Commons // CC BY-SA 4.03

There are a lot of parasites out there. Some estimates suggest that as many as half of all the species on earth live inside—and feed off—other species. One new study published online (which hasn't been peer reviewed yet) argues that the parasitoid wasps might be the largest single group of animals—a title generally thought to be held by beetles.

Practically every species has its own set of parasites, and even parasites have parasites. In many cases, a parasite's host is little more than a habitat where it can eat and breed. But some parasites have gone a step further, evolving ways to manipulate their hosts in ways that give the parasite a better shot at growing up and spreading its young far and wide. Their methods can be as deliciously gross as the worst imaginings of horror movie screenwriters. Here are 10 examples to inspire new terrors of the silver screen.

1. JEWEL WASP // AUSTRALIA, PACIFIC ISLANDS


The jewel wasp Ampulex compressa is iridescently beautiful, but it's a nightmare for the American cockroach. When a pregnant female wasp gets hold of a roach, she temporarily paralyzes its muscles with a sting, then threads her stinger up into the roach's brain, injecting a cocktail of chemicals that turn the roach into a zombie. The roach could move when the paralysis wears off, but now it doesn't want to. Instead, it allows the wasp to gently lead it by one antenna to her burrow, where she walls it in with one of her eggs. That egg will soon become a larvae that spends its first week on earth eating the living roach bit by bit before pupating and emerging as a wasp to continue the cycle.

2. NEMATOMORPH HAIRWORM // EUROPE

Everything seems normal for weeks after a long-horned grasshopper has drunk water containing the microscopic larvae of the hairworm Spinochordodes tellinii, but that changes as soon as the worm grows big enough to start yearning for a mate. That's when it secretes chemicals that change its host's brain chemistry, making deep water seem enticing to the insect. The grasshopper suddenly has a suicidal urge to take a long hop off a short pier, and as it drowns, the worm—now as much as three times as long as the insect it lived in—squeezes out of its host and swims off to find a mate. Other hairworm species prefer praying mantises or spiders as hosts, but it's the same endgame for them all.

3. PARASITIC BARNACLE // MARINE COASTS

Sacculina carcini
John Aplessed, Wikimedia Commons // Public Domain

A female Sacculina carcini starts its life like any other barnacle—as a tiny planktonic baby floating free in the ocean. But unlike your average barnacle, when she drifts onto a crab she doesn't just settle down and become a warty bump riding on its shell. Instead, she burrows into the crab and grows until she infiltrates every crevice of the crab's body. This can take years, but eventually she's big enough to inflate her bulbous reproductive structures through the crab's abdomen so microscopic males of her species can fertilize her eggs. Once that happens, her crabby host stops molting and growing; all it does is eat and take care of its parasite. Her babies are incubated inside the crab's abdomen, and since part of her is inside the crab's brain by now, she also hijacks its egg-caring behaviors—even male crabs nurture them—to aerate and disperse thousands of her own future mind-controlling brood.

4. ICHNEUMOID WASP // NORTH AMERICA

ichneumoid wasp
MirandaKate, Flickr // CC BY-NC 2.0

A female ichneumoid wasp Campoletis sonorensis sneaking up on a grazing caterpillar isn't looking for a meal for herself—she's shopping for a nose-to-tail larder for her young. The wasp injects one or two fertilized eggs under the caterpillar's skin, and just for good measure, squirts in a virus that will keep the caterpillar's immune system from attacking the invaders. When she flies away, the caterpillar goes right back to eating, but it's a dead grub walking: In a few days, the wormlike wasp larvae hatch inside the caterpillar. They'll spend a couple of weeks munching away at its guts until they grow large enough to burst through its body wall. Then, they spin cocoons—often beside or on the dead body of their host—and pupate into another generation of chest-busting parasitoids (which, unlike most parasites, always kill their hosts).

5. GREEN-BANDED BROODSAC FLATWORM // EUROPE AND NORTH AMERICA

A land snail's eyestalks are normally a pretty drab affair, but that all changes if the snail licks up bird droppings infected with larvae from the flatworm Leucochloridium paradoxum. The baby worms move into the snail's digestive gland, forming an asexual colony that can eventually make up a quarter of the snail's mass. As the colony matures, it starts packing members into bright green, squirming brood sacs that writhe up into the snail's eyestalks, swelling them into fat approximations of wriggling caterpillars. If that's not enough to grab a hungry bird's attention, those pulsing, writhing brood sacs can also break through the snail's body wall and crawl off to mimic a juicy grub on their own.

6. PHRONIMA AMPHIPOD // DEEP OCEAN WORLDWIDE


Freshwater and Marine Image Bank, Wikimedia Commons // Public Domain

The deep-sea amphipod genus Phronima is a literal body-snatcher. This parasitoid captures gelatinous salps—jet-propelled, filter-feeding planktonic animals that are closely related to vertebrates—and hollows them out with jaws and claws, consuming the salp's brain, gills, stomach, and muscles, and scraping its inner walls smooth. The salp body—technically still living—becomes a barrel-shaped, ocean-going home that the amphipod can maneuver like a miniature submarine. It might eventually be a full house, too—female Phronima keep their young in the barrel and care for them until they've grown.

7. RIBEIROIAN TREMATODE FLATWORM // NORTH AMERICA

deformed pacific chorus frog infected with ribeiroia ondatrae parasite
Brett A. Goodman, Pieter T. J. Johnson, Wikimedia Commons // CC BY 2.5

The horror starts when larvae of the parasitic flatworm Ribeiroia ondatrae leave the snail they used as a nursery and burrow into the tail of a bullfrog tadpole. When the tadpole metamorphoses into an adult frog—a period of time that varies between species—the flatworms form cysts around its developing legs, disrupting their growth in ways that damage or double them. The crippled, flatworm-infested frog can't jump away from predatory birds like herons, which gobble them up. The flatworm then spreads to new waterways wherever the bird poops.

8. GALL WASP // WORLDWIDE

gall wasp eggs
Justin 0 of 0, Flickr // CC BY-NC 2.0

Not even plants are safe from parasitism. Females of Cynipidae, the family of gall wasps, lay their eggs inside leaves or under bark, and their larvae make the plant cells surrounding them grow faster than they would normally, effectively forcing the plant to grow them a house. Weird, nonleafy shapes rise up out of the plant, filled with juicy nutritious tissues that feed the wasp larvae and surrounded by tough woody walls that protect it until it becomes an adult (more than a year in some species) and chews its way out of its safe space.

9. ENTOMOPATHOGENIC FUNGUS // NORTH AMERICA

goldenrod beetle infected by mind-controlling E. lampyridarum fungus
Steinkraus et al. in Journal of Invertebrate Pathology, 2017

Goldenrod soldier beetles depend on the family of flowering plants commonly known as asters, which includes goldenrods and daisies. The beetles eat the plants' pollen and mate in their shade. But if a beetle gets infected with the fungus Eryniopsis lampyridarum, it climbs up an aster's stem, clenches the base of a flower with its mandibles, and dies. Within a day, the fungus forces the dead beetle's wings open to expose its spores, which rain down on the hapless beetles below.

10. OPECOELID TREMATODE FLATWORM // PACIFIC MARINE REEFS

Coral colony infected by trematode Podocotyloides stenometra
Alamy

The tiny polyps that build stony corals are usually an inconspicuous brown. But that changes whenever a polyp inadvertently grabs a young Podocotyloides stenometra flatworm for a meal. Somehow, the trematode worm doesn't get digested—instead, it invades the polyp's tentacles, swelling them and turning them bright pink. The color is a bright billboard advertising deliciousness to butterflyfish on the reef, who eat the flashy polyps and spread the worm to other corals across the reef.

Could Gigantic Coconut Crabs Have Played a Part in Amelia Earhart’s Mysterious Disappearance? At Least One Scientist Thinks So

Getty Images
Getty Images

Amelia Earhart's disappearance during her attempt to fly around the world has captivated historians and conspiracy theorists for more than 80 years. One organization is now suggesting that her fate may have been sealed by giant crabs.

The International Group for Historic Aircraft Recovery (TIGHAR) believes that Amelia Earhart and navigator Fred Noonan may have landed their plane on Nikumaroro Island when they couldn't find their target, Howland Island, and that Nikumaroro's endemic crustaceans may have played a part in the ensuing mystery.

According to National Geographic, there are several clues supporting TIGHAR's theory. The large reef that hugs Nikumaroro’s coast makes it conducive to emergency aircraft landings. In 1940—just three years after Earhart’s disappearance—British colonists found 13 human bones beneath a ren tree on the island and shipped them to Fiji, where they were lost. The colony's administrator, Gerald Gallagher, sent a telegram back to England positing that it was Earhart’s skeleton. Then, in 2001, researchers uncovered U.S.-made artifacts around the ren tree including a jackknife, a woman’s compact, a zipper, and glass jars. The plot thickened even further in 2017, when four forensic bone-sniffing dogs all indicated that a human had indeed died at the site, though excavators failed to dig up any more evidence.

If those 13 bones beneath the ren tree did belong to the unfortunate castaway, where are the rest of her remains? Tom King, TIGHAR’s former chief archaeologist, thinks that coconut crabs can answer that question.

Nikumaroro is home to thousands of the colossal creatures, which can grow to a terrifying 3 feet across and weigh 9 pounds. They’re sometimes called robber crabs because of their penchant for absconding with objects that smell like food, and they’ll eat practically anything—coconuts, fruit, birds, rodents, other crabs, their own discarded body parts, and carrion.

It’s not unreasonable, then, to think that coconut crabs may have feasted on Earhart’s corpse and then taken her bones home with them. In one experiment to test the theory, TIGHAR researchers deposited a pig carcass on the island and filmed the aftermath. With the help of small strawberry hermit crabs, coconut crabs stripped the pig down to the bone in two weeks. After a year, some of the bones had been dragged 60 feet from the carcass’s original location, and some were never recovered at all.

King believes Earhart’s missing 193 bones could be hidden in the burrows of various coconut crabs. As in the pig experiment, crabs may have scattered some of Earhart’s bones dozens of feet away, but maybe not all of them—after all, the forensic dogs smelled bones near the ren tree that haven’t yet been located. Right now, TIGHAR is working with the Canine Forensics Foundation to further explore the area.

While we wait for more answers, dive into these other theories about Earhart’s disappearance.

[h/t National Geographic]

10 Juicy Facts About Leeches

Ian Cook
Ian Cook

Leeches get a bad rap, but they’re actually pretty cool once you get to know them—and we're finding out more about them, even today. Recently, a team led by Anna Phillips, curator of parasitic worms at the Smithsonian National Museum of Natural History, discovered a new species of medicinal leech (pictured above) in a Maryland swamp. We asked parasite expert and curator at the American Museum of Natural History Mark E. Siddall to share some surprising facts about the worms we love to hate. 

1. Not all leeches suck blood.

Hematophagous, or blood-feeding, species are only one type of leech. “The vast majority of species are [hematophagous],” Siddall tells Mental Floss, “but it depends on the environment. In North America, there are probably more freshwater leeches that don’t feed on blood than there are blood-feeders.” And even among the hematophagous species, there are not too many who are after you. “Very few of them are interested in feeding on human blood,” Siddall says. “Certainly they’ll do it, if they’re given the opportunity, but they’re not what they’re spending most of their time feeding on.” 

2. Leeches are everywhere.

Japanese leech on a log
Pieria, Wikimedia Commons // Public Domain

“Every continent on the planet has leeches, with the exception of Antarctica,” Siddall says. “And even then there are marine leeches in Antarctic waters.” Humans have co-existed with leeches for so long, according to Siddall, that just about every language has a word for leech. 

3. Leeches have made a comeback in medicine.

Bloodletting for bloodletting’s sake has fallen out of favor with Western physicians, but that doesn’t mean medicinal leeches are enjoying a cushy retirement. Today, surgeons keep them on hand in the operating room and use them as mini-vacuums to clean up blood. “That is a perfectly sensible use of leeches,” Siddall says. Other uses, though, are less sensible: “The more naturopathic application of leeches in order to get rid of bad blood or to cure, I don’t know, whatever happens to ail you, is complete hooey,” he says. How on Earth would leeches take away bad blood and leave good blood? It’s silly.” 

4. Novelist Amy Tan has her own species of leeches.

Land-based leeches made an appearance in Tan’s 2005 book Saving Fish from Drowning, a fact that instantly put the author in leech researchers’ good graces. “There are not a lot of novels out there with terrestrial leeches in them,” Siddall says. So when he and his colleagues identified a new species of tiny terrestrial leeches, they gave the leech Tan’s name. The author loved it. “I am thrilled to be immortalized as Chtonobdella tanae,” Tan said in a press statement. “I am now planning my trip to Queensland, Australia, where I hope to take leisurely walks through the jungle, accompanied by a dozen or so of my namesake feeding on my ankles.”

5. Leeches can get pretty big.

The giant Amazon leech (Haementeria ghilianii) can grow up to 18 inches and live up to 20 years. And yes, this one’s a blood-feeder. Like all hematophagous species, H. ghilianii sticks its proboscis (which can be up to 6 inches long) into a host, drinks its fill, and falls off. Scientists thought the species was extinct until a zoologist found two specimens in the 1970s, one of whom he named Grandma Moses. We are not making this up.

6. Leeches make good bait.

Many walleye anglers swear by leeches. “A leech on any presentation moves more than other types of live bait," pro fisher Jerry Hein told Fishing League Worldwide. "I grew up fishing them, and I think they're the most effective live bait around no matter where you go." There’s an entire leech industry to provide fishers with their bait. One year, weather conditions kept the leeches from showing up in their typical habitats, which prevented their collection and sale. Speaking to CBS news, one tackle shop owner called the absence of leeches “the worst nightmare in the bait industry.”

7. Leech scientists use themselves as bait.

Siddall and his colleagues collect and study wild leeches. That means hours of trekking through leech territory, looking for specimens. “Whether we’re wandering in water or traipsing through a bamboo forest,” Siddall says, “we are relying on the fact that leeches are attracted to us.” Do the leeches feed on them? “Oh my god, yes. We try to get them before they feed on us … but sometimes, obviously, you can’t help it.”

8. Leech sex is mesmerizing.

Like many worms, leeches are all hermaphroditic. The specifics of mating vary by species, but most twine themselves together and trade sperm packets. (The two leeches in the video above are both named Norbert.)

9. Some leech species make surprisingly caring parents. 

“There’s a whole family of leeches that, when they lay their eggs, will cover them with their own bodies,” Siddall says. “They’ll lay the eggs, cover them with their bodies, and fan the eggs to prevent fungus or bacteria from getting on them, and then when the eggs hatch, they will attach to the parent. They’re not feeding on the parent, just hanging on, and then when the parent leech goes to its next blood meal it’s carrying its offspring to its next blood meal. That’s pretty profound parental care, especially for invertebrates.”

10. You might be the next to discover a new leech species. 

Despite living side-by-side with leeches for thousands of years, we’ve still got a lot to learn about them. Scientists are aware of about 700 different species, but they know there are many more out there. “I’ll tell you what I wish for,” Siddall says. “If you ever get fed on by a leech, rather than tearing off and burning it and throwing it in the trash, maybe observe it and see if you can see any color patterns. Understand that there’s a real possibility that it could be a new species. So watch them, let them finish. They’re not gonna take much blood. And who knows? It could be scientifically useful.”

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