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.

The Weird, Disturbing World of Snail Sex

iStock
iStock

Romance is rare in the animal kingdom. Instead of wooing their partners before copulating, male ducks force themselves onto females, depositing genetic material with spiky, corkscrew penises. Then, there's tardigrade sex, which is less violent but not exactly heartwarming. Females lay eggs into a husk of dead skin. The male then ejaculates onto the eggs while stroking the female, and the whole process can take up to an hour.

But you can't talk about disturbing mating rituals in nature without mentioning snails. If you're unfamiliar with snail sexuality, you may assume that snail sex falls on the vanilla side: The mollusks, after all, are famous for being slow-moving and they don't even have limbs. But if you have the patience to watch a pair of snails going at it, you'll notice that things get interesting.

The first factor that complicates snail sex is their genitalia. Snails are hermaphrodites, meaning individuals have both a male set and female set of parts, and any two snails can reproduce with each other regardless of sex. But in order for a couple of snails to make little snail babies, one of them needs to take on the role of the female. That's where the love dart comes in.

The love dart, technically called a gypsobelum, isn't exactly the Cupid's arrow the name suggests. It's a nail-clipping-sized spike that snails jab into their partners about 30 minutes before the actual sex act takes place. The sliver is packed with hormones that prepare the receiving snail's body for sperm. Depending on the species, only one snail might release the dart, or they both might in an attempt to avoid becoming the female of the pair. You can watch the action in the video below.

For sex to be successful, both snails must insert their penises into the other's vaginal tracts at the same time. Both snails deposit sperm, and the strength of the love dart ultimately determines whether or not that sperm fertilizes their partner's eggs.

That's assuming the snail survives the little love-stab. In human proportions, the love dart is the equivalent of a 15-inch knife. Fortunately, snails are resilient creatures, and gastropod researcher Joris Koene tells KQED he's only ever seen one snail die from the transfer.

Snails also have a way of making it up to their partners after skewering them with a hormone stick. Their sperm deposit contains a dose of fortifying nutrients, something scientists refer to as a nuptial gift. It may not equal the energy expended during sex, but its enough to give them a small post-coital boost.

10 Facts About Rosacea

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iStock

Rosacea, a skin condition characterized by redness and swelling, is incredibly common: A recent study found that an estimated 300 million people worldwide suffer from it. Here’s what you need to know about the condition.

1. IT HAS A LONG HISTORY.

According to the National Rosacea Society (NRS), rosacea was first described in the 14th century by a French surgeon named Dr. Guy de Chauliac; he called it goutterose (“pink drop” in French) or couperose and noted that it was characterized by “red lesions in the face, particularly on the nose and cheeks.”

2. SCIENTISTS AREN’T SURE WHAT CAUSES IT ...

But they have some theories. According to the NRS, “most experts believe it is a vascular disorder that seems to be related to flushing.” Scientists also think that because rosacea seems to run in families, it might be genetic. Other things—like mites that live on the skin, an intestinal bug called H pylori (common in those who have rosacea), and a reaction to a bacterium called bacillus oleronius—could also play a role in causing the condition. One 2015 study suggested an increased risk among smokers.

3. … BUT SOME PEOPLE ARE MORE LIKELY TO HAVE IT THAN OTHERS.

Though people of all ages and skin tones can get rosacea, fair skinned people between the ages of 30 and 50 with Celtic and Scandinavian ancestry and a family history of rosacea are more likely to develop the condition. Women are more likely to have rosacea than men, though their symptoms tend to be less severe than men’s. But men are more likely to suffer from a rare rosacea side effect known as rhinophyma, which causes the skin of the nose to thicken and become bulbous. It’s commonly—and mistakenly—associated with heavy drinking, but what exactly causes rhinophyma is unclear. According to the NRS, “The swelling that often follows a flushing reaction may, over time, lead to the growth of excess tissue (fibroplasia) around the nose as plasma proteins accumulate when the damaged lymphatic system fails to clear them. Leakage of a substance called blood coagulation factor XIII is also believed to be a potential cause of excess tissue.” Thankfully, those who have rhinophyma have options available for treatment, including surgery and laser therapy.

4. THERE ARE FOUR SUBTYPES.

According to the American Academy of Dermatology (AAD), rosacea “often begins with a tendency to blush or flush more easily than other people.” All rosacea involves redness of some kind (typically on the nose, cheeks, chin, and forehead), but other symptoms allow the condition to be divided into four subtypes: Erythematotelangiectatic rosacea is characterized by persistent redness and sometimes visible blood vessels; Papulopustular rosacea involves swelling and “acne-like breakouts”; Phymatous rosacea is characterized by thick and bumpy skin; and Ocular rosacea involves red eyes (that sometimes burn and itch, or feel like they have sand in them [PDF]), swollen eyelids, and stye-like growths.

5. IT’S NOT THE SAME AS ACNE.

Though rosacea was once considered a form of acne—"acne rosacea" first appeared in medical literature in 1814—today doctors know it’s a different condition altogether. Though there are similarities (like acne, some forms of rosacea are characterized by small, pus-filled bumps) there are key differences: Acne involves blackheads, typically occurs in the teen years, and can appear all over the body; rosacea is a chronic condition that occurs mainly on the face and the chest and typically shows up later in life.

6. YOU CAN FIND IT IN CLASSIC ART AND LITERATURE.

Both Chaucer and Shakespeare likely made references to rosacea. Domenico Ghirlandaio’s 1490 painting An Old Man and His Grandson seems to depict rhinophyma, and some believe that Rembrandt’s 1659 self-portrait shows that the artist had rosacea and rhinophyma.

7. IT MAY BE TRIGGERED BY CERTAIN FOODS AND ACTIVITIES.

According to the National Institutes of Health (NIH) [PDF], people report that everything from the weather to what you eat can cause rosacea to flare up: Heat, cold, sunlight, and wind, strenuous exercise, spicy food, alcohol consumption, menopause, stress, and use of steroids on the skin are all triggers.

8. THERE ARE A NUMBER OF MYTHS ABOUT ROSACEA.

No, it’s not caused by caffeine and coffee (flare ups, if they occur, are due to the heat of your coffee) or by heavy drinking (though alcohol does exacerbate the condition). Rosacea isn’t caused by poor hygiene, and it’s not contagious.

9. THERE ARE SOME PRETTY FAMOUS PEOPLE WITH ROSACEA.

Sophia Bush, Cynthia Nixon, Kristin Chenoweth, Bill Clinton, and Sam Smith all have rosacea. Diana, Princess of Wales had it, too. W.C. Fields had rosacea and rhinophyma, and Andy Warhol may also have suffered from those conditions.

10. IT CAN’T BE CURED—BUT IT CAN BE TREATED.

The NRS reports that “nearly 90 percent of rosacea patients [surveyed by NRS] said this condition had lowered their self-confidence and self-esteem, and 41 percent reported it had caused them to avoid public contact or cancel social engagements.” Dr. Uwe Gieler, a professor of dermatology at the Justus-Liebig-University in Giessen, Germany, and one of the authors of the report Rosacea: Beyond the Visible, said in a press release that "People with rosacea are often judged on their appearance, which impacts them greatly in daily life. If their rosacea is severe, the symptoms are likely to be more significant also, from itching and burning to a permanently red central facial area. However, even people with less severe rosacea report a significant impact on quality of life."

Which makes it all the more unfortunate that there’s not a cure for the condition. Thankfully, though, there are treatments available.

There are no tests that will diagnose rosacea; that’s up to your doctor, who will examine your medical history and go over your symptoms. Doctors advise that those with rosacea pay attention to what triggers flare-ups, which will help them figure out how to treat the condition. Antibiotics might be prescribed; laser therapy might be used. Anyone with rosacea should always wear sunscreen [PDF] and treat their skin very, very gently—don't scrub or exfoliate it. The AAD recommends moisturizing daily and avoiding products that contain things like urea, alcohol, and glycolic and lactic acids.

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