4 Parasites We Wouldn't Mind Hosting, After All

It's parasites week here at mental_floss, which we kicked off two days ago with the release of our newest video, "Attack of the Parasites." Now, while it's true that there are all kinds of compelling reasons to avoid becoming infested with parasites -- especially by the kinds that cause things like river blindness and elephantiasis of the genitalia -- there are also a few reasons to make nice with our tiny, opportunistic compatriots. Here are four.

1. Pseudacteon, the "decapitating fly"

Nobody likes fire ants. Where I grew up in Southern Florida, they were a major nemesis to unfettered, shoeless outdoor romping; one false step could mean a foot covered in biting, welt-inducing fire ants. In fact, ever since they were accidentally imported from South America via cargo ship in the 1930s, they've spread like an annoying, predator-less plague from coast to coast, infesting at least 18 states. So far, the only measures introduced to deal with them have been stopgap at best -- sprinkling poison on the mounds, for instance. That is, until now.

ant1.gifMeet Pseudacteon, a parasitic fly from South America. Pseudacteon, like most living creatures, loves to reproduce. The important distinction between it and other flies, however, is where Pseudacteon lays its eggs: inside the heads of fire ants. Get ready for an awesomely grody cycle-of-life: the larvae develop by feeding on the muscle and nervous tissue in the head. After about two weeks, they cause the ant's head to fall off by releasing an enzyme that dissolves the membrane attaching the ant's head to its body. The fly pupates in the detached head capsule (pictured above!). Hence: the decapitating fly! Currently, industrious agricultural scholars are importing them from South America in the hopes that they'll do rid us of our fire ants. Godspeed, little decapitators.

2. Worm therapy

A rare bit of good news from the world of gastrointestinal maladies: swallowing the eggs of a certain type of parasite worm may actually help cure Crohn's disease. The basic theory is this: in countries where people's exposure to parasites is high, disorders of the immune system like Crohn's, multiple sclerosis and type 1 diabetes are rare. In ultra-sanitized industrialized nations like the U.S., they're common. According to researchers, we may have hygiened our way into a few diseases that certain types of parasites actually help prevent, and by re-introducing them into the body -- that is, with "worm therapy" -- we may actually be able to combat those conditions.

Specifically, treatment with the eggs of the intestinal parasite helminth Trichuris suis may be a safe and effective treatment for Crohn's disease, according to the results of a small, preliminary trial conducted at the University of Iowa in Iowa City. T. suis is not a natural human parasite, but primarily affects pigs.

3. The blepharipa schineri fly

cat2.jpgIf swallowing worm eggs isn't your thing, then maybe you can get behind this: the fuzzy, half-inch-long blepharipa schineri does for the gypsy moth what the decapitating fly does for the fire ant. (Well, it doesn't actually decapitate the moth, but the end result is the same: no more moths. It achieves this by laying eggs in pre-moth gypsy caterpillars, where they hatch and prevent them from growing into moths.)

What's so terrible about gypsy moths? Just ask a park ranger: gypsy moths eat the leaves of some of our most popular shrubs and trees, from oak to beech to poplars. In the Eastern U.S., the moths are well-established over at least 60 million acres, defoliating and killing hundreds of varieties of trees. If you don't like the sound of that, you just might like the sound of what the fly does to the moth:

A parasite of the gypsy moth, the B. schineri fly kills unlucky gypsy moth caterpillars that accidentally eat fly eggs while munching on leaves. A gray-black speck about the size of a thumbtack point, the fly egg hatches inside the caterpillar's stomach. The transparent B. schineri maggot that emerges will later poke holes in the caterpillar's gut, then wriggle its way to the nerve cord that runs the length of the body. While the gypsy moth caterpillar transforms into a pupa--a pre-moth that slumbers in a silky, loosely woven cradle--the B. schineri maggot feeds on the host's innards, slowly killing it.

Gross? Sure. Useful? Definitely. Lucky for us, moths are this fly's only breeding ground.

4. It Makes the Ladies Happy

Quite literally: the Toxoplasma parasite, found primarily in cat feces, is known to have a mood-altering effect on humans, which differs depending on the sex of the human. In a study conducted by parasitologist Jaroslav Flegr of Charles University in Prague, some infected women were likely to become more outgoing and warm-hearted, whereas some infected men became more jealous and suspicious. (Not everyone is mood-altered by cat poo; it's a small, though statistically significant, percentage.) When it's not changing our moods, the Toxoplasma is trying to spread itself by making rats who come into contact with it act fearless, which makes it easier for them to be caught by cats (who then become infected, etc).

Live Smarter
Nervous About Asking for a Job Referral? LinkedIn Can Now Do It for You

For most people, asking for a job referral can be daunting. What if the person being approached shoots you down? What if you ask the "wrong" way? LinkedIn, which has been aggressively establishing itself as a catch-all hub for employment opportunities, has a solution, as Mashable reports.

The company recently launched "Ask for a Referral," an option that will appear to those browsing job listings. When you click on a job listed by a business that also employs one of your LinkedIn first-degree connections, you'll have the opportunity to solicit a referral from that individual.

The default message that LinkedIn creates is somewhat generic, but it hits the main topics—namely, prompting you to explain how you and your connection know one another and why you'd be a good fit for the position. If you're the one being asked for a referral, the site will direct you to the job posting and offer three prompts for a response, ranging from "Sure…" to "Sorry…".

LinkedIn says the referral option may not be available for all posts or all users, as the feature is still being rolled out. If you do see the option, it will likely pay to take advantage of it: LinkedIn reports that recruiters who receive both a referral and a job application from a prospective hire are four times more likely to contact that individual.

[h/t Mashable]

Dean Mouhtaropoulos/Getty Images
Essential Science
What Is a Scientific Theory?
Dean Mouhtaropoulos/Getty Images
Dean Mouhtaropoulos/Getty Images

In casual conversation, people often use the word theory to mean "hunch" or "guess": If you see the same man riding the northbound bus every morning, you might theorize that he has a job in the north end of the city; if you forget to put the bread in the breadbox and discover chunks have been taken out of it the next morning, you might theorize that you have mice in your kitchen.

In science, a theory is a stronger assertion. Typically, it's a claim about the relationship between various facts; a way of providing a concise explanation for what's been observed. The American Museum of Natural History puts it this way: "A theory is a well-substantiated explanation of an aspect of the natural world that can incorporate laws, hypotheses and facts."

For example, Newton's theory of gravity—also known as his law of universal gravitation—says that every object, anywhere in the universe, responds to the force of gravity in the same way. Observational data from the Moon's motion around the Earth, the motion of Jupiter's moons around Jupiter, and the downward fall of a dropped hammer are all consistent with Newton's theory. So Newton's theory provides a concise way of summarizing what we know about the motion of these objects—indeed, of any object responding to the force of gravity.

A scientific theory "organizes experience," James Robert Brown, a philosopher of science at the University of Toronto, tells Mental Floss. "It puts it into some kind of systematic form."


A theory's ability to account for already known facts lays a solid foundation for its acceptance. Let's take a closer look at Newton's theory of gravity as an example.

In the late 17th century, the planets were known to move in elliptical orbits around the Sun, but no one had a clear idea of why the orbits had to be shaped like ellipses. Similarly, the movement of falling objects had been well understood since the work of Galileo a half-century earlier; the Italian scientist had worked out a mathematical formula that describes how the speed of a falling object increases over time. Newton's great breakthrough was to tie all of this together. According to legend, his moment of insight came as he gazed upon a falling apple in his native Lincolnshire.

In Newton's theory, every object is attracted to every other object with a force that’s proportional to the masses of the objects, but inversely proportional to the square of the distance between them. This is known as an “inverse square” law. For example, if the distance between the Sun and the Earth were doubled, the gravitational attraction between the Earth and the Sun would be cut to one-quarter of its current strength. Newton, using his theories and a bit of calculus, was able to show that the gravitational force between the Sun and the planets as they move through space meant that orbits had to be elliptical.

Newton's theory is powerful because it explains so much: the falling apple, the motion of the Moon around the Earth, and the motion of all of the planets—and even comets—around the Sun. All of it now made sense.


A theory gains even more support if it predicts new, observable phenomena. The English astronomer Edmond Halley used Newton's theory of gravity to calculate the orbit of the comet that now bears his name. Taking into account the gravitational pull of the Sun, Jupiter, and Saturn, in 1705, he predicted that the comet, which had last been seen in 1682, would return in 1758. Sure enough, it did, reappearing in December of that year. (Unfortunately, Halley didn't live to see it; he died in 1742.) The predicted return of Halley's Comet, Brown says, was "a spectacular triumph" of Newton's theory.

In the early 20th century, Newton's theory of gravity would itself be superseded—as physicists put it—by Einstein's, known as general relativity. (Where Newton envisioned gravity as a force acting between objects, Einstein described gravity as the result of a curving or warping of space itself.) General relativity was able to explain certain phenomena that Newton's theory couldn't account for, such as an anomaly in the orbit of Mercury, which slowly rotates—the technical term for this is "precession"—so that while each loop the planet takes around the Sun is an ellipse, over the years Mercury traces out a spiral path similar to one you may have made as a kid on a Spirograph.

Significantly, Einstein’s theory also made predictions that differed from Newton's. One was the idea that gravity can bend starlight, which was spectacularly confirmed during a solar eclipse in 1919 (and made Einstein an overnight celebrity). Nearly 100 years later, in 2016, the discovery of gravitational waves confirmed yet another prediction. In the century between, at least eight predictions of Einstein's theory have been confirmed.


And yet physicists believe that Einstein's theory will one day give way to a new, more complete theory. It already seems to conflict with quantum mechanics, the theory that provides our best description of the subatomic world. The way the two theories describe the world is very different. General relativity describes the universe as containing particles with definite positions and speeds, moving about in response to gravitational fields that permeate all of space. Quantum mechanics, in contrast, yields only the probability that each particle will be found in some particular location at some particular time.

What would a "unified theory of physics"—one that combines quantum mechanics and Einstein's theory of gravity—look like? Presumably it would combine the explanatory power of both theories, allowing scientists to make sense of both the very large and the very small in the universe.


Let's shift from physics to biology for a moment. It is precisely because of its vast explanatory power that biologists hold Darwin's theory of evolution—which allows scientists to make sense of data from genetics, physiology, biochemistry, paleontology, biogeography, and many other fields—in such high esteem. As the biologist Theodosius Dobzhansky put it in an influential essay in 1973, "Nothing in biology makes sense except in the light of evolution."

Interestingly, the word evolution can be used to refer to both a theory and a fact—something Darwin himself realized. "Darwin, when he was talking about evolution, distinguished between the fact of evolution and the theory of evolution," Brown says. "The fact of evolution was that species had, in fact, evolved [i.e. changed over time]—and he had all sorts of evidence for this. The theory of evolution is an attempt to explain this evolutionary process." The explanation that Darwin eventually came up with was the idea of natural selection—roughly, the idea that an organism's offspring will vary, and that those offspring with more favorable traits will be more likely to survive, thus passing those traits on to the next generation.


Many theories are rock-solid: Scientists have just as much confidence in the theories of relativity, quantum mechanics, evolution, plate tectonics, and thermodynamics as they do in the statement that the Earth revolves around the Sun.

Other theories, closer to the cutting-edge of current research, are more tentative, like string theory (the idea that everything in the universe is made up of tiny, vibrating strings or loops of pure energy) or the various multiverse theories (the idea that our entire universe is just one of many). String theory and multiverse theories remain controversial because of the lack of direct experimental evidence for them, and some critics claim that multiverse theories aren't even testable in principle. They argue that there's no conceivable experiment that one could perform that would reveal the existence of these other universes.

Sometimes more than one theory is put forward to explain observations of natural phenomena; these theories might be said to "compete," with scientists judging which one provides the best explanation for the observations.

"That's how it should ideally work," Brown says. "You put forward your theory, I put forward my theory; we accumulate a lot of evidence. Eventually, one of our theories might prove to obviously be better than the other, over some period of time. At that point, the losing theory sort of falls away. And the winning theory will probably fight battles in the future."


More from mental floss studios