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There are a lot of creepy creatures in the world, and even the microcosmos is no place to escape them. And perhaps one of the most unsettling creatures to us here on Journey to the Microcosmos is the mite.

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There are a lot of creepy creatures in the world, and the microcosmos is no place to escape them. For every adorable tardigrade waving its stubby legs around, there are also countless nightmarish organisms lurking.

And perhaps one of the most unsettling creatures to us here on our Journey to the Microcosmos is the mite. It’s not enough for these tiny arachnids to remind us of every nightmare we’ve ever had involving spiders. These organisms also produce different compounds that manage to be unsettling in their own unique way.

So today, we are going to revisit some of our previous videos about mites, following along through the varied lives different species live, and the…well let’s call them gifts …that they leave along the way. And we’ll start out with the mites that might be sharing a room with you, right now. One of the most frequent questions we get asked  on Journey to the Microcosmos is how James,   our master of microscopes, stays safe  while gathering and studying samples.   After all, as beautiful as the microcosmos is,  there are plenty of parasites and pathogens in   there that we’d prefer to keep under  the microscope and out of our bodies.  But while James has simple and effective  guidelines to protect his health—like   making sure he always washes his hands before and  after handling samples, and never venturing into   a pond with an open wound—there are times  when those measures don’t quite cut it.   These are the times when no matter how much  you protect yourself outside or inside,   the microcosmos gets the best of you.

These are the times of the dust mite.  Now we don’t usually start these videos with  a warning, but we’re going to do that today.   While working on this video, at least 4  members of the Journey to the Microcosmos team   found themselves having a bit of a  crisis about how clean their homes were.  If you’ve found yourself sneezing and wheezing and   running around miserable with a runny  nose because of dust, this arachnid   is probably the culprit—though perhaps  not in the way you would expect.  Dust mites are small in the grand scheme of  things, but large in the microcosmos, hitting just   around 300 micrometers in length. Their bodies are  decked out with four pairs of legs ending in feet   that act like suction cups as they wander in their  quest for three things: water, food, and darkness.  Dust mites love humidity because their  lives depend on it. They don’t drink water   so much as they osmosis it into them, relying on  a salt-filled gland near their mouth to absorb   water vapor from the air around them.

So if their  surroundings become more arid, an adult dust mite   will wither away until it eventually dies. This is a challenge for dust mites that live   in places with seasons, where wet and rainy falls  give way to dry winters. To survive those shifts,   they rely on the resilience of their  younger brethren—the nymphs—whose   forms are able to withstand the lack of moisture.

The seasons of the dust mite’s life was one of the   important clues that helped scientists in the 20th  century understand their role in dust allergies.   Scientists identified dust as the source of some  kind of allergen in the 1920s, but they were not   sure what it was exactly about dust that did it.  They just knew that people all over the globe   suffered from dust allergies, and that these  allergies were often seasonal, peaking in the   autumn, particularly after warm, humid summers2. And other possible sources, like animal dander   or mold, just didn’t quite fit right with the  seasonality of the allergy. But in the 1960s,   scientists in the Netherlands and Japan realized  that the dust mite might be the culprit.   They’re found in large numbers in the dust that  lines the unwashed and untouched corners of our   homes, their populations peaking in time with the  runny noses and bleary eyes of dust allergies.  But while experiments confirmed that mites  really were the source of people’s sensitivities   to house dust, it wasn’t clear what made them  so special.

So, we’ll get to that in a bit...  James often finds dust mites in the humidity  chambers he uses to keep his microbes alive.   These chambers are made up of a  dish lined with wet toilet paper,   which is just about all a dust mite needs to feel  right at home—especially when there’s potentially   some delicious microbes to munch on. So to keep  those other microbes from becoming a mite meal,   James has to regularly clean out  and disinfect the humidity chamber.  Now, that cleaning might get rid of the  dust mites in the humidity chamber, but   the problem is that our houses are full of  food for them because our houses are full of   us—of flakes from our skin that shed and gather  all around and sustain the invisible mite.  And this is a problem not just because it  means the mite can thrive in our homes.   It’s a problem because food means poop. Over  the course of its life, a mite will produce   about 1000 pieces of poop that are roughly the  size of a grain of pollen.

Inside those bits of   fecal matter are enzymes that help the dust mite  eat its own poop and get nutrients that it might   not have gotten the first time around. But should the dust mite choose to not   revisit its prior meals, the feces will float  around the room, attached to other particles   until eventually they settle down—perhaps on  a pillow, or on a pet’s bed, or a car seat.   It’s like we’re living in a gigantic snow globe,  except that the snow... is dust mite feces.  In 1981, researchers confirmed the bad news about  this animal’s poop— people are allergic to it.   To be more specific, they confirmed  that dust mite poop contains specific   proteins that many people are allergic to. So if you’re airing out some sheets and you start   sneezing, what you might actually be reacting  to is dust mite feces flying around the air.  Now, we apologize for this mental image but it  is reality, and it has embedded in our heads,   so we have to share it with you as well.

But  we can offer what might be a small comfort:   there is another allergen from dust  mites that has nothing to do with poop.  Dust mites have a fairly lengthy mating process,  sometimes taking up to two days to finish—this   is a pretty lengthy time for any organism, but  especially for an animal that’s only got about   100 total days to live. Over the course of their  life, the female dust mite will lay up to 80 eggs,   which hatch into larvae that then go through  several different stages of development   before becoming adults With each passing stage,   the dust mite sheds its exoskeleton, leaving  behind its youth. And that exoskeleton provides   some of the other allergens for people react to.

But though that is something people are sometimes   allergic to, it really is mostly just the poop  that sets off people’s allergies. So I guess there   really wasn’t that much comfort there after all. And even for a trained and cautious   microbiologist, dust mites can  become an unwelcome surprise.  Once, James brought home some samples taken from  a water dish that his neighbor left outside for   their cat.

The surface was covered in tiny round  things, and James thought they might be rotifers.  But when he looked at the surface of the scum  under the microscope, there were no charming   rotifers to be found. It was mites, just  hundreds of them crawling around the slide.  It was so unpleasant that James  immediately bleached the slide.  Now, he’s not sure if that sample is the reason,  but for days after, James kept sneezing and   having to deal with a runny nose, all of  which pointed to a potential mite invasion.  Fortunately though, our homes are not a utopia  for dust mites. What they really need is dark,   which is why they prefer to dig themselves deep  into carpets and other soft things that give them   space to burrow4.

Dust mites have a harder time  with materials like suede that are difficult to   hide themselves in5, and they usually avoid  hard surfaces that are exposed to light.  So for James, his weapons against  the mite invasion were clear:   a vacuum, a mattress cleaner, and a strong  UV light bulb. It is one of the more ignoble   ends to one of our organisms. We don’t like  to hurt them, unless they are hurting us.   But I am sure there’s a dust mite somewhere in our  homes right now, settling into a soft, dark abode   of its own, with hardly a care in the world for  the battle that was waged to bring you this video.  If you have not abandoned this video yet to go clean your room, we do appreciate it.

Because next up, we have water mites, who are perhaps less of a scourge to us than dust mites, but who are still capable of producing their own strange compounds with… uncomfortable implications. For those of you afraid of spiders, the  microcosmos probably seems like a safe haven.   When you’re scanning through a microscopic  ocean full of single-celled organisms,   the likelihood of a spider crawling  across your screen feels comfortingly low.   The few times we’ve seen a spider under the  microscope, it’s because we put it there.  But safe as the microcosmos might  seem from a surprise spider attack,   it would be misleading to pretend that it’s  completely free of spider-like sightings. Because   even at this small scale, you could find yourself  subject to an ambush of the arachnid sort.  These are water mites, relatives of spiders  in that they are also members of the Arachnid   class.

And the resemblance is uncanny,  especially with the eight legs waving around.  But that detail aside, there is something about this water mite that looks   more like a cartoon spider, something  you might have doodled in a notebook.  For one, there’s the eyes, those simple dots.  Water mite species usually have two pairs,   which act mainly to detect light. It’s much  less intimidating to stare into the eyes of a   water mite than into the eight eyes of a spider. Another reason for the cartoon spider-iness of   some water mites is down to a defining aspect  of their shape.

Spiders have segmented bodies,   with an abdomen that is distinct from  the cephalothorax that holds its head.   But water mites aren’t segmented. Instead,  those different parts are all fused together.   In the case of this particular species, the  final result is round and kind of adorable.  So now we’re going to disrupt that cuteness by  bringing up a creature we’ve talked about before,   one that’s more closely related to water mites  and one that does not evoke any sense of cuteness.   We’re talking about dust mites, which are part of  the same superorder of mites called Acariformes.  If you haven’t watched our episode about  dust mites before, you should check it   out after watching this video, especially if  you’re looking for motivation to clean your   room. Because without spoiling too much, the main  thing to know about dust mites is that their poop   is, it’s not great.

I’m bringing that up now   because while water mite poop might not evoke  the same concern that dust mite poop does,   it is still fascinating. Their excretory system  is made of a large tube connected to a pore.   The tube takes in waste from the mite’s version  of blood, called hemolymph. And in the tube,   the waste is stored as yellow or white  crystals.

To clear out its storage of crystals,   the mite simply moves its muscles to push  everything out through its excretory pore.  From the studies we’ve found on other mites  with similar systems, our best guess is that   these poops are guanine crystals, produced by  the mite’s own body as it breaks down nutrients.  Now crystal poop is weird. But the weirder thing is that crystaline poop is not the   weirdest thing that water mites excrete. But before we get there, let’s talk about just how   red some of our water mites are.

They’re so red  that they seem like walking drops of blood. They are not actually chock-full of blood though; the red color is likely just some kind of carotenoid   that turns the water mite crimson. And for a time, scientists believed   that the red color was a way for  these species of water mites to flash   a warning signal to fish, a sort of “Do not eat  me” expressed solely through threatening hue.  But like why?

Why did scientists think fish would  heed this warning anyway? Why would a fish   bother to listen to a water mite  when it could be eating instead?  Well, many water mite species have an  approach to warding off predators that   is…sticky. Water mites have little globe-shaped  organs dotting their bodies called glandularia,   each with their own little opening and a little  bristle-y hair called a seta.

When something, say,   a fish, brushes up against that hair, it triggers  the glandularia into releasing a milky fluid into   the water, where it mixes into a tackier,  more viscous substance. And for predators,   the idea of having to wade through some gloppy  mess to get to your food is probably unappealing.  So when the scientists saw, in the context of their own  experiments, that fish seemed to quickly stop trying to eat water mites, they decided  that the red coloring was the water mites’   way of telling the fish, “We’re the sticky prey.” But while it’s possible the fish do learn not to   pick out these water mites for food,  the idea that the red color exists   specifically as a warning to predators does not  hold up to the basics of how these particular   species live. Red water mite species tend  to be found in transient pools of water,   places that fish don’t often find themselves.  So the likelihood that they would have evolved   this trait for the purpose of warning fish is low.  It’s more likely that the pigments are a way of   protecting them from ultraviolet light.

It just maybe happened to also protect them from fish as well.  And the sticky fluid that makes them unappealing to  fish also has another use: reproduction.   In one genus called Arrenurus, the males use it to   hold the females still during copulation. This is part of a wider spectrum of weird   reproductive behaviors. On one end, there are  the species like the ones we just mentioned,   which engage very directly and  physically with each other.  On the other end of the spectrum, there are water  mite species where the sexes don’t feel the need   to interact at all to make reproduction happen.  They don’t communicate, they don’t touch.

The   males simply deposit spermatophores somewhere for  their female counterparts to find them and pick them up.  And then, somewhere between the directly  copulating water mites and the cold shoulder   water mites, there are the dancers. They’re  sort of like the second group in that the males   drop off their spermatophores. But then they  actually stick around, mostly so they can draw   females in and help them find the spermatophores.

And this is where dancing comes in. Sometimes this   involves vibrating their legs  to mimic their favorite prey,   drawing the attention (and aggression) of a  wandering female. Other times though, this means   waltzing together as a pair, moving in circles  with careful pauses to pick up the spermatophores.  We obviously don’t have video of that or  we would be showing it to you.

But at some point,  some scientist watched this happen. Someone  watched the dance of the mating water mites,   and then they carefully documented it.  Just like someone saw the mite-averse fish,   and the crystal poops, and the many other strange  things that make up the lives of water mites. Before we dive into our next mite video, I want to take a moment to thank today’s sponsor, Manukora Honey.

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Okay. Let’s get back to the mites… So far, we’ve been describing the ways that mites make things that make other creatures uncomfortable. But to cast them solely as the excretion villains of the microcosmos would be unfair.

In fact, if you’re a fan of cheese, there’s a good chance that you might actually be a fan of mites too… even if you don’t know it yet. In May 2013, a shipment of around 1.5 tons of cheese was refused entry into the United States. The cheese in question was a spherical, orange variety known as mimolette that’s sometimes compared to cantaloupes in looks, and lemons in taste.

There’s nothing super startling about that description— nothing to suggest, at least, that this is a suspicious cheese. But according to the Food and Drug Administration, this shipment of mimolette had a problem: it had mites. If the idea of mites on your cheese makes your skin crawl, we have good and bad news for you.

The good news is that most cheeses are not usually filled with so many mites that the FDA decides to take action. The bad news? Well…this mite was scraped from the rind of a Milbenkase, a cheese from Germany that is also known for its lemon-y flavor.

And if you like milbenkase and mimolette but hate mites… the bad news is, you’ve been eating a lot of mites. The footage we’re showing you today was sampled and recorded by Chloe Savard, one of our guest masters of microscopes. The last time we featured her videos, we were looking at the hidden structures behind our favorite fruits and vegetables.

This time, she brought us cheese. Like right now, you are looking at the rind of a milbenkase. There’s a rough sort of graininess to the texture, and you can imagine that it might feel bumpy beneath your fingers.

But you might also notice that some of those bumps are moving. And that feeling under your fingertips is now probably a lot less pleasant to imagine. And that sensation might become worse when you imagine putting some of that cheese into your mouth, knowing that some of those mites will find their way into your body.

Now as gross as it is to imagine, and maybe it isn't. It's just eating animals which lots of people do all the time. I cannot blame the mites, Cheese is delicious!

Except that the mites aren't actually here because the cheese tastes good. It’s really more the reverse: the cheese tastes good to us because the mites are there. Milbenkase is the cheese that it is because of those mites.

It begins as a low-fat curd cheese, kind of like cottage cheese, mixed with salt and herbs, and then it is ripened in a wooden box. Inside of that box are cheese mites, more specifically the species Tyrolichus casei. These mites feed on rye flour that is added to the box, producing digestive juices full of enzymes that help carry out the fermentation needed to develop the cheese.

And after anywhere from a month to a year, you can eat the cheese, mites and all. It’s estimated that there are around 2000 mites in each square centimeter of the rind. Mimolette cheese is also made with the help of these mites, though the species and the processes are a little different.

The mites of mimolette eat the crust of the cheese and leave behind tiny holes that help the cheese breathe. The mite also excretes compounds that impact the ripening of the cheese… which is another not so pleasant image. Despite their differences, milbenkase and mimolette both owe their flavor to the mites.

Scientists have traced the lemony taste of the cheese directly to a compound called neral, which is found in lemon oil… and in cheese mite secretions. Remove the cheese mites from the process, and you take away that flavor. In the case of mimolette, though, the mites are brushed off the cheese before shipment.

And yet enough do remain that sometimes, they can reproduce into a population that is large enough to alarm the FDA. According to news reports in 2013, the FDA didn’t have an official limit on how many mites could be present on cheese. But ideally, they wanted there to be no more than 1 mite per square centimeter.

And the shipment that was making its way into the US had more mites than that, so the FDA stepped in. For us casual cheese eaters, that intervention might seem reasonable. Mites are pests.

We see them again and again in the microcosmos, and they often turn up in places that we do not want them and they cause various conditions that are not comfortable. And in some people who spend a long time working with these cheeses, mites can cause allergies. But for the people who love the cheese, the crackdown on mimolette was not well-received.

This is a cheese that has been around for centuries without much issue. Plus, let’s face it, cheese often includes some strange ingredients, plucked straight from the invisible world of the microcosmos. Like let’s take a moment with this clip.

Just looking at it, where do you think it came from? This is not a trick question or anything. If you saw the blue, and you immediately thought “blue cheese,” well, you are correct.

These samples were taken from the blue veins of the cheese, which are actually dug out by a fungus called Penicillium roqueforti. These molds used to be found naturally in milk and cheese, and people would even take spores from the best cheese of the last batch and inoculate it on bread to use again. But today, spores are often added during the cheese-making process.

As the fungus grows, it breaks down fats in the cheese and produces new flavors The good news is that it is also safe for consumption. As is cheese made with Geotrichum candidum, a fungus used in the production of a number of soft cheeses, where it grows on the surface of the rind. In fact, it is so widely used in French cheese that one estimate suggested that a French person will eat around 8 kilograms of cheese containing Geotrichum candidum in just one year.

Geotrichum candidum lives in a variety of habitats, including soil and grass... but also in raw milk, which is why it’s often found in raw milk cheeses. And with enzymes that break down protein and fat, the fungus can shape the aroma and taste of the cheese overall. In some, it even leave behind a velvety surface to the cheese.

The overall effect of the fungus, though, depends on the strain of Geotrichum candidum. Some create what’s known as “peau de crapaud,” or “toad skin.” And some are known to impart a greasy or bitter quality. And there are times when perhaps those traits are exactly what you want.

In a way, it’s like art made from the microcosmos, a careful adjustment to suit a person’s taste. And maybe that is what made the response to the FDA’s mimolette blockage so strong. On the one hand, it’s cheese.

There are plenty of cheeses available at the store, and to those of us who are perhaps of less discerning taste, it seems like there should be plenty of alternatives should your favorite cheese be held up at the border. But art is art, even if some of the artists are members of the microcosmos. They weave blue veins or construct velvety rinds or add hints of lemony brightness to the flavor, and through centuries of traditions, we have been the wielders and consumers of an art they know purely as survival.

And our own tastes, it seems, have won out. We haven’t found a lot of official information detailing the FDA’s stance on mimolette today. But we did find a 2015 post on a cheese blog that mentions seeing the cheese return to local stores.

Which is good news for everyone… except maybe for the mites that find their way into your stomach. Now we have talked quite a bit about excretions today, including the most notable one of all: poop. But what is poop without a butt to produce it?

Well, that is the question at the heart of our last video today, which is all about face mites. Yes, the mites that live on your face. Because at the center of it all is a surprisingly important question: how many mite butts are on your face?

A lot happened in the year 2022. Economies shifted, reigns ended, wars began. So it is okay if you missed out on this little bit of we think very important news: Demodex have buttholes.

Now perhaps you have never thought to wonder about this. Perhaps you have never even heard of a Demodex before and you’re just slowly putting together that it must be related to the creature that we are watching right now. Yeah, the one that looks like a tardigrade but weirder, which says a lot given that tardigrades already look pretty weird to us.

So you might wonder why we would care if a Demodex has a butthole or not. Well, we care because they live on our face. Demodex are a genus of tiny mites that build their lives around the hair follicles of various animals.

And there are two species that are found on humans: Demodex folliculorum and Demodex brevis. They each have their own preferred nooks on our faces, with Demodex folliculorum preferring hair follicles, and Demodex brevis preferring our sebaceous glands. The mites we are looking at had the distinction of coming straight from the face of our master of microscopes, James, who saw a little black dot on his forehead and was curious what was going on inside.

So he simply scraped the spot with the side of a microscope slide and took a look. But these mites don’t always localize themselves in neat little dots, so sometimes scientists have to turn to other measures to study them. In one NPR interview, a scientist described applying glue to a microscope slide and then sticking it to a person’s forehead so as they peeled the slide off, the mites would peel off too.

And look, we get it. Learning that there are little animals crawling around your face, it might be a little unsettling. Even James, who spends just about every day thinking about microbes, found himself initially repulsed by what he found on his skin.

But then he realized that they look like tardigrades with big butts. And if we can all collectively love tardigrades the way that we seem to, perhaps we can find some space in our hearts for these mites. They’re even cute under the harsh glare of our UV light!

The mites are tiny, less than a millimeter in length. And you can see two distinct halves to their body. At one end—the tardigrade end, as we like to call it in a purely unscientific way—are eight stubby legs waving behind the Demodex’s mouth.

At the other end are their gastrointestinal organs and their genitals. Those spherical droplets in their body are oil droplets, the digested remains of the sebum and moisturizer that Demodex like to eat from our skin. Now, if at this moment, your mind is conjuring up images of the demodex wandering your face in search of oil to eat, you can rest easy.

Well, for now at least. They’re probably not wandering, they're just chilling out inside your pores. At night though, Demodex do like to party.

They emerge from your pores in search of each other, looking for other mites to mate with. And when they are done, they head back to your pores to lay their eggs. An adult Demodex folliculorum lays around 20-24 eggs in your hair follicles.

Within three to four days, the young Demodex will hatch, emerging with only six legs weirdly enough. As they develop into adulthood, the other two legs will develop as well. Their life span will end a few weeks later, at which point the dead mites will decompose in your follicles or sebaceous glands, turning the tiny little pockets of your skin into little mite graveyards.

It's a lot, I know. We keep trying to say that Demodex are cute actually, but then we talk about little mite mating parties and mite graveyards on your skin, and none of that is cute. But here’s the thing: we pretty much all have them.

If you’re watching this video, you probably have Demodex living in your face. And if you don't now, you will eventually. Now they usually spread through physical contact, though a 2015 study found that we tend to primarily pass them on via close contact with our family members rather than strangers.

And when they have found your face, they’ll probably stick around, hiding in your pores and other spaces that make them hard to scrub out. Generally, that’s fine. Demodex don’t wreak much havoc on your skin.

They can become too abundant, creating a distinctive white sheen that dermatologists call Demodectic frost. That excess of mites is usually connected to a decline in the immune system. But these cases are very rare.

For a time, there was a theory that Demodex could cause rosacea, because they were thought to not have a butthole. What do those things have in common with each other? Well the idea was that without an anus, the Demodex couldn’t poop.

Instead, the Demodex would spend their short lives accumulating waste in large cells in their body, and storing it away. And when they died, the feces would burst from their bodies, releasing bacteria that could then cause rosacea. There are enough correlations between Demodex and the occurrence of rosacea to leave us considering that there could be a connection between the two.

But we are here to vindicate the mites a little. Because that mechanism is based on an idea that would turn out to be very wrong, the idea that Demodex don’t have an anus. In 2022, scientists were studying the genes within Demodex.

And among their results are some microscopy images and these words, which we hope will become a classic in the history of butthole science: There have been several reports that Demodex does not have an anus, and when Demodex dies, the accumulated waste spills into the pores of the skin and leads to inflammation; this is not correct. We’ve talked before about just how mysterious and confusing the history of anus evolution is, and so we were excited to hear this news. But the other results of the scientist’s genetic study of the Demodex are also worth learning more about because they reveal just how strange our relationship with these creatures is.

In particular, the scientists found that the Demodex are surprisingly simple, relying on a small number of proteins to survive. This likely drives their nocturnal behavior, because they lack the compounds that allow their relatives to survive at all in the daytime. And this might be the result of just how lonely the Demodex mites are, in an ecosystem built out of our skin where they face few threats and little competition.

They’re doing so well that they may require less than they once did to survive. And that has been pushing them—at least according to these scientists—to a future where they might be symbionts with us, much like bacterial endosymbionts that have become fully embedded in their hosts. That is, for now, just a hypothesis.

If there comes a day when the hypothesis is fulfilled, well what do we do then? Do we consider them weird and creepy, and maybe even a little rude? Or do we accept them as part of us, as inevitable as every other cell in our body?

Or perhaps it is both, as nuanced as any other experience we have with our bodies. Wonderful and terrible, all at once. Thank you for coming on this journey with us as we explore the unseen world that surrounds us.

One thing that you've got to know, as a Patreon patron of Journey to the Microcosmos, is you don't know where the next episode is going. But you trust us, to go in the direction that we want to go in to discover what we can discover by not looking big but looking small. The people on the screen right now, they are our Patreon patrons, and they are the reason that we can do this.

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