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.

10 Facts About the Winter Solstice, the Shortest Day of the Year

Matt Cardy/Getty Images
Matt Cardy/Getty Images

Amid the whirl of the holiday season, many are vaguely aware of the approach of the winter solstice, but how much do you really know about it? Whether you're a fan of winter or just wish it would go away, here are 10 things to note—or even celebrate—about the shortest day of the year.

1. The winter solstice HAPPENS ON DECEMBER 21/22 in 2019.

Sun setting behind a tree in the winter
buxtree/iStock via Getty Images

The date of the winter solstice varies from year to year, and can fall anywhere between December 20 and December 23, with the 21st or 22nd being the most common dates. The reason for this is because the tropical year—the time it takes for the sun to return to the same spot relative to Earth—is different from the calendar year. The next solstice occurring on December 20 will not happen until 2080, and the next December 23 solstice will not occur until 2303.

2. The winter solstice hAPPENS AT A SPECIFIC, BRIEF MOMENT.

sun setting through the trees
yanikap/iStock via Getty Images

Not only does the solstice occur on a specific day, but it also occurs at a specific time of day, corresponding to the instant the North Pole is aimed furthest away from the sun on the 23.5 degree tilt of the Earth's axis. This is also the time when the sun shines directly over the Tropic of Capricorn. In 2019, this moment occurs at 4:19 a.m. UTC (Coordinated Universal Time) on December 22. For those on Eastern Standard Time, the solstice will occur at 11:19 p.m. on December 21. And regardless of where you live, the solstice happens at the same moment for everyone on the planet.

3. The winter solstice mARKS THE LONGEST NIGHT AND SHORTEST DAY OF THE YEAR FOR THE NORTHERN HEMISPHERE.

sun setting over Central Park
rmbarricarte/iStock via Getty Images

As most are keenly aware, daylight hours grow shorter and shorter as the winter solstice approaches, and begin to slowly lengthen afterward. It's no wonder that the day of the solstice is referred to in some cultures as the "shortest day of the year" or "extreme of winter." New York City will experience 9 hours and 15 minutes of sunlight, compared to 15 hours and 5 minutes on the summer solstice. Helsinki, Finland, will get 5 hours and 49 minutes of light. Barrow, Alaska, will not have a sunrise at all (and hasn't since mid-November; its next sunrise will be on January 22), while the North Pole has had no sunrise since October. The South Pole, though, will be basking in the glow of the midnight sun, which won't set until March.

4. ANCIENT CULTURES VIEWED THE WINTER SOLSTICE AS A TIME OF DEATH AND REBIRTH.

snow on tree branches
Eerik/iStock via Getty Images

The seeming death of the light and very real threat of starvation over the winter months would have weighed heavily on early societies, who held varied solstice celebrations and rites meant to herald the return of the sun and hope for new life. Scandinavian and Germanic pagans lit fires and may have burned Yule logs as a symbolic means of welcoming back the light. Cattle and other animals were slaughtered around midwinter, followed by feasting on what was the last fresh meat for several months. The modern Druidic celebration Alban Arthan reveres the death of the Old Sun and birth of the New Sun.

5. THE  shortest DAY of the year MARKS THE DISCOVERY OF NEW AND STRANGE WORLDS.

Pilgrims landing at Plymouth Rock
Hulton Archive/Getty Images

The Pilgrims arrived at Plymouth on December 21, 1620, to found a society that would allow them to worship freely. On the same day in 1898, Pierre and Marie Curie discovered radium, ushering in an atomic age. And on December 21, 1968, the Apollo 8 spacecraft launched, becoming the first manned moon mission.

6. THE WORD SOLSTICE TRANSLATES ROUGHLY TO "SUN STANDS STILL."

colorful sunset
a_Taiga/iStock via Getty Images

Solstice derives from the Latin scientific term solstitium, containing sol, which means "sun," and the past participle stem of sistere, meaning "to make stand." This comes from the fact that the sun’s position in the sky relative to the horizon at noon, which increases and decreases throughout the year, appears to pause in the days surrounding the solstice. In modern times, we view the phenomenon of the solstice from the position of space, and of the Earth relative to the sun. Earlier people, however, were thinking about the sun's trajectory, how long it stayed in the sky and what sort of light it cast.

7. STONEHENGE IS ALIGNED TO THE SUNSET ON the WINTER SOLSTICE.

Stonehenge sunset
jessicaphoto/iStock via Getty Images

The primary axis of the megalithic monument is oriented to the setting sun, while Newgrange, another structure built around the same time as Stonehenge, lines up with the winter solstice sunrise. Some have theorized that the position of the sun was of religious significance to the people who built Stonehenge, while other theories hold that the monument is constructed along natural features that happen to align with it. The purpose of Stonehenge is still subject to debate, but its importance on the winter solstice continues into the modern era, as thousands of hippies, pagans, and other types of enthusiasts gather there every year to celebrate the occasion.

8. ANCIENT ROMANS CELEBRATED REVERSALS AT THE MIDWINTER FESTIVAL OF SATURNALIA.

Saturnalia parade
A Saturnalia celebration in England in 2012.
Christopher Furlong/Getty Images

The holiday, which began as a festival to honor the agricultural god Saturn, was held to commemorate the dedication of his temple in 497 BCE. It quickly became a time of widespread revelry and debauchery in which societal roles were overturned, with masters serving their slaves and servants being allowed to insult their masters. Mask-wearing and play-acting were also part of Saturnalia's reversals, with each household electing a King of Misrule. Saturnalia was gradually replaced by Christmas throughout the Roman Empire, but many of its customs survive as Christmas traditions.

9. SOME TRADITIONS HOLD THAT DARK SPIRITS WALK THE EARTH ON THE WINTER SOLSTICE.

Snowy woods
Serjio74/iStock via Getty Images

The Iranian festival of Yalda is celebrated on the longest night of the year. In pre-Islamic times, it heralded the birth of Mithra, the ancient sun god, and his triumph over darkness. Zoroastrian lore holds that evil spirits wander the Earth and the forces of the destructive spirit Ahriman are strongest on this long night. People are encouraged to stay up most of the night in the company of one another, eating, talking, and sharing poetry and stories, in order to avoid any brushes with dark entities. Beliefs about the presence of evil on the longest night are also echoed in Celtic and Germanic folklore.

10. SOME THOUGHT THE WORLD WOULD END ON THE 2012 WINTER SOLSTICE.

snowy woods with sun through the trees
Delpixart/iStock via Getty Images

December 21, 2012 corresponds to the date 13.0.0.0.0 in the Mesoamerican Long Count calendar used by the ancient Maya, marking the end of a 5126-year cycle. Some people feared this juncture would bring about the end of the world or some other cataclysmic event. Others took a more New Age-y view (literally) and believed it heralded the birth of a new era of deep transformation for Earth and its inhabitants. In the end, neither of these things appeared to occur, leaving the world to turn through winter solstices indefinitely, or at least as long as the sun lasts.

A version of this story originally ran in 2015.

Cats Make Facial Expressions, But Not Everyone Can Read Them

takoburito/iStock via Getty Images
takoburito/iStock via Getty Images

Science has finally confirmed what humans have suspected for centuries: Cats are inscrutable creatures prone to peculiar behavior. Some of us, however, are still capable of picking up on their subtle emotional cues, including facial expressions, without relying on clues like tails, ears, or whiskers.

This new evidence of a cat’s slightly malleable face comes from a study in the journal Animal Welfare. Researchers at the University of Guelph in Ontario, Canada, recruited 6329 participants to watch a series of 20 video clips featuring cats reacting to either a positive or negative event. A positive interaction was defined as a feline approaching a human for a treat or an owner-identified action the cat traditionally found pleasant, like climbing into a favorite spot. A negative response was when a cat was confronted with something it wanted to avoid, was prevented from going into an area or outside, or was displaying an obvious sign of distress, like growling. (Sounds were edited out.) Most clips were from YouTube, though some were submitted by veterinarians and university colleagues. Breeds with long hair that might obscure facial changes were omitted. Most respondents were cat owners, and 74 percent were women 18 to 44 years old.

Using these brief clips, the researchers asked subjects to classify the cats as exhibiting positive or negative behavior by relying only on closely cropped footage of a cat’s face. They couldn’t rely on the tail or any other body language. The result? The average score was just 59 percent correct, accurately identifying a cat’s mood in an average of 12 out of the 20 clips. These humans, in other words, had little idea what a cat was experiencing based solely on their faces.

So why do researchers think they have any expression at all? Roughly 13 percent of subjects scored well on the test, getting at least 15 of the 20 questions correct. Those that did well were generally people who had extensive experience with cats, like veterinarians. That led researchers to conclude that people can become more attuned to the subtle flickers of emotion that may pass over a cat’s face.

“They could be naturally brilliant, and that’s why they become veterinarians,” Georgia Mason, a behavioral biologist and the study’s senior author, told The Washington Post. “But they also have a lot of opportunity to learn, and they’ve got a motivation to learn, because they’re constantly deciding: Is this cat better? Do we need to change the treatment? Does this cat need to go home? Is this cat about to take a chunk out of my throat?”

The paper appears to offer encouraging evidence that “cat whisperers” really do exist. If you’re curious whether you could be one of them, you can take a shortened version of the video test online.

[h/t Washington Post]

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