Spider Tales 4: The stuff of (urban) legends: Dissecting three widespread spider myths

Urban legends are fascinating. These pieces of modern folklore are as creepy as they are entertaining, and provide a wonderful insight into how entirely made-up, far-fetched stories, can be believed and passed on, as long as they sound scary and shocking enough. Of course, they are often told for fun and entertainment, but there are also many people who sincerely believe in some of them and accept them as fact.

A big part of their impact comes from their tendency to tap into the widespread fears and beliefs of the place and time they exist in. These cultural context elements, which give birth to the urban tales and transpire through them, can be highly specific to one particular location (such as a particularly creepy and mysterious abandoned building in a specific town) or be more vague, and representative of the concerns and anxieties of an entire demographic.
The fear of all things foreign and unfamiliar, and of these foreign threats making an unwelcome intrusion in our world of familiarity and perceived safety, for instance, is a recurring theme in urban legends, particularly those that arose in times of international tensions such as the Cold War in the 1960s and 70s, or the conflicts in Iraq in the early 2000s. 

Quite frequently, the "foreign threat" in question is an exotic, often venomous or dangerous animal (or at least, depicted as such in the tale), and, more often than not, a spider (although the bestiary of urban legends also includes rats, scorpions, snakes and even alligators!). 

From our human perspective, which tends to see human and mammalian traits as "normal", and anything that deviates from this "norm" as "weird", spiders are extremely strange, and their behaviours and abilities seem almost alien-like.
At the same time, they're also among our most common and conspicuous commensals (wild species that live alongside us and share our habitats); there's no place, anywhere on the planet, that is permanently inhabited by humans but not by spiders.
Thus, they perfectly embody the intrusion of the wild, foreign, "alien" element in our familiar and "safe" universe. No wonder they are so often featured in urban legends: unfortunately for them, they have exactly the right profile.

Familiar, but at the same time wild, strange and shrouded in mystery, spiders occupy a very special place in modern folklore

In addition to that (and probably partly because of it), spiders are the object of a fairly common phobia (although far less common than one would think) and, more importantly, of a widespread and normalised mindset of hate, fear and disgust, largely fed and encouraged by media and cultural products, from films to internet memes.

Since the early days of cinema, spiders have been often picked as horrific antagonists or intimidating decor elements, but very rarely as anything else (image source)

In terms of reputation compared to their actual medical significance, spiders are probably the most exaggeratedly maligned and misunderstood animals on earth, possibly even more so than snakes or sharks. Any news about spiders, even good ones such as a threatened species making a comeback or research highlighting how precious and helpful they are to ecosystems and agriculture, are depicted by the media in an invariably negative, generally distorted and sometimes downright ridiculous way.

The actual news behind this title? A rare and threatened (and fairly large, but not nearly "hand-sized") species (Dolomedes plantarius) whose populations are finally on the rise in some protected areas in the UK, thanks to conservation efforts. "Fact distortion" is quite an understatement here.

Unfortunately, this trend is not restricted to lowly tabloids selling fear as a cheap way to bait readers; even wildlife documentaries and animal show hosts indulge way too often in sensationalism and exaggeration when talking about spiders.
Misinformation is such a standard when it comes to these animals that it has made us extremely gullible about them, and about what they can or cannot do.
While urban legends about holes leading to Hell, giant prehistoric sharks hiding in the Mariana Trench or vengeful ghosts appearing in mirrors understandably raise some eyebrows, the three spider tales that follow, although entirely fictitious and not much less far-fetched, are frequently accepted as facts by people who sincerely believe in them. 

These tales are worth dissecting, because there is often a distorted truth behind them. Although the stories are 100% fictional, the human imagination is much more limited than we give it credit for, so they are often based, or at least distantly inspired, by actual phenomena. The good news is, the kernel of reality they hide is generally small, and always much more reassuring and mundane than the myth.

1. The spiders in the mouth

This one is more of a factoid¹ than an actual urban legend: according to the Internet, spiders sometimes enter a sleeper's open mouth, and the average human swallows about 8 spiders a year (some variations say eight in our lifetime, some say up to 50 in a year, but the truth is, you can eat as many as you want, no one will judge you) in their sleep.  

Apparently, this myth has been circulating at least since the 70s, but its popularity really took off when it started spreading on the Internet. While its origin and early spread through oral transmission is difficult, if not impossible, to dig up, its second life online is much easier to trace.
The first recorded instance of the factoid¹ on the Internet is from the famous fact-checking website Snopes.com, in 2001. Ironically, the first known online occurrence of this myth is therefore an article debunking it, which claims its original source was a newspaper piece about online misinformation, written by Lisa Birgit Holst, published in 1993 in the journal PC Professional. The factoid¹ was allegedly mentioned by Lisa Holst as a social experiment, and originally taken from Lucy Clausen's book Insect Fact and Folklore, published in 1954. 

The thing is, upon closer investigation, there is no trace of Lisa Holst's article anywhere, or of the journal PC Professional, or even of Lisa Birgit Holst herself. There is no mention, either, of that factoid¹ in Insect fact and folklore, which does not contain any information about spiders, except in the introduction, to say that they are not insects.
If you try to look up Lisa Birgit Holst or her article on Google, you'll find a disclaimer from Snopes confirming that the article was actually a joke and a social experiment, with a fabricated factoid¹ and made-up sources, and that "Lisa Birgit Holst" is an anagram for "this is a big troll".
The entire thing was meant to encourage people to be careful about what they read on the Internet, and not only to check the validity of the information, but also its sources. Needless to say, it backfired spectacularly.

That factoid became so famous on the Internet that it has inspired an endless supply of sarcastic, absurd memes and jokes (artist: Chris (Simpsons artist))

That little piece of Internet folklore is very interesting, because it provides great insight into how untrue, and honestly not very believable, false information can be shared to such an extent that basically anyone who had an Internet connection in the 2000s and 2010s has heard about it.
It shows that as long as a factoid¹ is striking and surprising, it doesn't have to sound too realistic to spread efficiently. It's unlikely that many of the people who shared it actually believed in it, or had even thought it through; however, it's such a perfect attention-grabbing "fun fact" that even those who didn't really swallow it (pun intended) still passed it on. 

The common "explanation" for that myth is that spiders mistake the human mouth for a source of fresh water, and enter it to drink saliva.
The thing is, a sleeper's saliva isn't exactly clean, fresh water. It's a lukewarm, sticky, stinky mix of water, salt, enzymes, degraded food scraps, and bacteria (many more than when we're awake). While we sleep, our production of saliva drops considerably, resulting not only in smaller, more concentrated amounts, but also in a dirtier, stinkier mouth, because of bacterial build-up.
Meanwhile, spiders are incredibly sensitive creatures, whose legs and pedipalps are covered with receptors, including mecanoreceptors that detect vibrations and air currents, and chemoreceptors that "smell" and "taste" what they touch. A spider walking on a sleeping human is capable of identifying that this large, warm, salty, sour thing that moves and vibrates is alive, enormous, and thus potentially dangerous and best avoided. Although spiders can sometimes find themselves walking on us by accident, they will generally try to get down and away as soon as possible.
Seen with a spider's senses, a sleeper's open mouth is a huge, wet, abnormally warm hole, dripping with salty, sticky fluids and exhaling a strong stream of rank, hot, humid air, stinking of bacteria and decaying organic matter. Not exactly a safe and inviting hideout.
Spiders haven't survived for more than 300 million years by randomly entering potential predators' mouths to their certain death.

If a spider ever entered your mouth, it probably looked like that

 

Finally, let's consider one last ridiculous point: how exactly would we have discovered that we eat on average eight spiders in our sleep in a year? It's supposed to happen while we sleep, and therefore unbeknownst to us.
It's not like there is a statistically significant number of people out there who agreed to get filmed while sleeping every night for a year or even for their entire life to see if a spider crawls into their mouth, and how often it happens...

Maybe that's how we know (artist:MyGumsAreBleeding)

There's one way you may have accidentally swallowed a spider before; however, you were not asleep. Tiny spiders, and spiderlings (babies) of larger species, can travel very long distances by soaring through the air, using strands of silk as a para-sail, taking off thanks to atmospheric electrical charges and ascending air currents. That passive flight, called ballooning, can carry the spiders over hundreds, sometimes thousands, of kilometres.

The tiny "money spiders" (family Linyphiidae) are ballooning specialists, and keep doing it as adults; this behaviour inspired a belief that they'll bring fortune to those they land onto, hence their name

The thing is, ballooning spiders can't really control their route, and behave like "aerial plankton", carried by the winds; that means their flight could, unfortunately, drive them right to a gruesome death, inhaled by a mouth or a nostril.
The good news is, only tiny spiders can balloon, so if it ever happens (or happened) to you, you probably won't even realise it; you'll just think you swallowed a midge or another tiny insect.

 

2. The exploding cactus

As the tale goes, someone (in almost all versions, a woman, for some reason) brought back a rare cactus (or a yucca, depending on the versions) from some foreign place (most of the time, it's Mexico, southwestern USA, or another country in arid parts of the American continent, but there are many versions of the story, including a British one where the plant was simply bought at Marks & Spencer's, or Ikea) to their home.
A few days later, as the person is watering or misting the plant, they notice that it seems to react oddly, generally by faint movements or sounds (depending on the versions, it vibrates, shivers, hums, or looks and/or sounds like it's breathing). Intrigued, they call a knowledgeable authority (some kind or plant expert, or, in other versions, a friend, a neighbour, or the police) and ask if the phenomenon is normal. Instead of providing a calm, informative and botanical explanation, the expert urges the main protagonist to get out of the house immediately and lock all doors and windows.
While, or right after they do, the plant suddenly explodes as thousands of tarantulas, which hatched from eggs laid inside its trunk, burst out and invade the house.
In most versions, the expert alerted by the main protagonist immediately made a call to some authorities (the police, the firefighters or the Agricultural Department), and while the explosion happens, an intervention unit in Hazmat suits raids the house and immediately destroys the deadly arachnids.
There's another version with an identical storyline, but which features scorpions instead of tarantulas.
Of course, there are more gruesome variations of the tale, where there's no call and no intervention, or where one of the family members is too slow to get out of the house, and gets bitten to death (or to amputation) by the spiders. There's even one where the poor family dog is left behind and devoured!

This tale is fairly old, dating back at least to the early 70s, hence its many variations. Its origin is fairly difficult to trace (probably in North America), as in the last 50 years, it has popped up in various places in North America, many European countries, Australia, and probably elsewhere.
Because of its longevity, it has been abundantly and repeatedly debunked.
It's a textbook example of the "foreign invasion" trope which is so common in urban legends, particularly those born during the Cold War.
Like the similar "Mexican pet" story, where a woman brings back from Mexico an "adorable chihuahua" which turns out to be an aggressive, oversized sewer rat, this legend is primarily meant to be a cautionary tale. 

While most messages that could be taken from these tales are laced with xenophobia and sexism (as the kind-hearted but clueless person who unwittingly takes the "big bad dirty foreign threat" back to the "safe, sanitary, civilised homeland", eventually putting lives in danger, is, of course, always a woman), there's one that is worth remembering: don't randomly poach wild plants and animals from their natural habitat to bring them back home.
Not only is this a highly unethical practice that can threaten wild populations of the species and/or cause it to become invasive elsewhere, but it could also land you in big trouble. If that species happened to be a protected one, or if you crossed a border with very strict regulations regarding the trade and circulation of wild species, you'd have a seriously bad time.

Animals get most of the attention, but most invasive species, including many of the most damaging to environments, are plants. In many cases, the invasion started with people treating the plant like a harmless, decorative commodity, and bringing it back home just because it looks pretty.

However, that trouble would not be of the "eight-legged freaks" kind. That entire "plant spewing venomous arachnids everywhere" thing is poppycock.
For starters, tarantulas (family Theraphosidae) do not lay eggs inside random plants and leave. They are actually fairly dedicated mothers, which guard and protect their egg sac until the spiderlings (baby spiders) are able to fend for themselves and disperse.
Same applies to scorpions: they give birth to live babies (called pulli), soft and vulnerable, which immediately crawl on their mom's back and stay there until they're big and strong enough to survive on their own.
When they eventually disperse, it's slowly, by walking. Their life cycle does not involve any explosive hatching from a plant. If you happened to have a tarantula or scorpion releasing its offspring in your house, you'd just notice it by finding an unusually high (compared to the amount you normally see, which could be zero or a few, depending on where and how you live) number of babies crawling around.

Scorpions don't lay eggs inside plants; they give birth to live young, which stay on their mother's back until they're big enough to fend for themselves

The timeline is another indication that the tale is fake: both tarantulas and scorpions are long-lived, slow-growing animals. Hatching from eggs and growing to adult, or at least to substantial size, takes months or even years. Some New World tarantula species, for instance in the genus Brachypelma from Central America, take as much as ten years to reach maturity!
Meanwhile, in the tale, a few days are allegedly enough for them to hatch and grow so large they make the plant burst... 

Finally, the last unrealistic element is that in the story, these Mexican tarantulas are (of course) said to be extremely dangerous. However, in reality, there is no extremely dangerous tarantula species anywhere on the American continent. While some "Old World" tarantula species (from Asia, Africa and Australia) have medically significant (but not deadly) venom, "New World" species (those from the Americas) are known for the typically milder effects of their venom on humans. Of course, a bite is still painful, but it will not be life-threatening, and unlikely to require any medical attention.
Actually, many tarantula species from North and Central America are immensely popular in the pet trade, as their relatively mild venom and generally passive disposition (although there are exceptions) make them suitable even for beginner keepers.

Central American tarantulas, such as this Tliltocatl albopilosum, are very popular as pets for their attractive colours, large size, (generally) laid-back temperament and ease of care, although they are extremely slow growers

Tarantulas of the deadly, cactus-exploding, dog-devouring kind are, fortunately, fiction.
Interestingly, though, there is a kernel of truth in that story, and it's surprisingly much bigger than in our two other urban legends: it turns out that finding exotic spiders on potted plants (but not inside the plant) not only happens, but is not exactly uncommon.

So common, in fact, that many spider species have extended, or are extending their range significantly by travelling with plants. Heated nurseries and garden centres are a true spider heaven: stable and high temperatures, high humidity, lots of hiding spots, and an abundance of insects and arachnids to prey upon, including pest species such as aphids and spider mites (which makes their presence in nurseries beneficial and valuable).

Probably originating from the southeast of Europe and western Asia, Uloborus plumipes is very common in garden centres and potted plants (so much that it is known as the "garden centre spider" in the UK) and now has an almost worldwide distribution

Their presence in nurseries causes them to often show up in homes, as they are unknowingly brought in with store-bought live plants. However, don't be afraid that your freshly bought succulent may bring in a crawling horde of giant spiders; most of these species are very small, which is why they could travel unnoticed in the first place, and are, as the vast majority of spiders is, harmless. 

One of the largest, and the closest thing to a tarantula that regularly travels with live plants, is a large Mygalomorph from Spain, Macrothele calpeiana, the Andalusian funnel-web spider. Despite its large size, it can travel unnoticed as, like many Mygalomorphs, it tends to hide underground, in the substrate.
This spider's backstory is a highly unusual one: this species used to be regarded as very rare, threatened and endemic from a tiny area in the south of Spain, with very specific habitat requirements. Twenty years ago, it was largely restricted to cork oak forests, in the south of Andalusia. Thus, when it started popping up in potted olive trees, arachnolgists were not only surprised, but worried: it could have been a sign that olive tree plantations were encroaching on native cork oak forests, destroying precious habitat for unique species.

Immature male Macrothele calpeiana, accidentally transported to France with an olive tree

However, the real reason turned out to be quite the opposite: Macrothele calpeiana actually seems to be much hardier and more tolerant than anticipated, and is actually spreading! Assisted by accidental exports with potted olive trees, it has established beyond the original limits of its range. Breeding populations have been found in many parts of Andalusia, Extremadura and Algarve in Portugal, but also much further north, in places where it was previously assumed to be unable to settle durably: around the cities of Alicante and Barcelona in Spain, and even in northern Italy!
Rumours of established populations in the south of France need scientific investigation, but, based on its presence in Italy, are not as improbable as they would have sounded 20 years ago.

In red, Macrothele calpeiana's original range; in blue, areas where newly established breeding populations have been found

Apart from these established (or possibly established) populations, Macrothele calpeiana is also a fairly common find in potted olive trees all over Europe. Andalusia is a major exporter of olive-based products and olive trees throughout Europe, so the spiders has been found, alive or dead, in the pots of trees imported to various countries: France, Belgium, the Netherlands, Germany, Italy and the United Kingdom have confirmed records (most commonly in France and Italy), but it has probably turned up, unrecorded, elsewhere as well. With a 35 mm long, jet black body, large fangs and powerful legs, Macrothele calpeiana definitely looks impressive and is the largest native spider in western Europe, so the accidental finds often cause a certain commotion and local press coverage.

Its appearance is strongly reminiscent of the Sydney funnel-web spider (Atrax robustus) and both species used to be included in the same family (Hexathelidae). This has led to false assumptions about the Andalusian funnel-web's bite, which is sometimes said to be medically significant, or even dangerous.
The thing is, recent studies have shown that the hypothetic relationships between the different Mygalomorph families were mostly wrong and based on features that were actually the result of convergent evolution (traits that independently evolve into similar states in unrelated groups).
In other words, among Mygalomorphs, a lot of different species look very much alike, without actually being closely related.
Among these families which were deeply remodelled based on recent analyses on DNA, RNA or proteins, was the family Hexathelidae, and the Andalusian funnel-web and Sydney funnel-web are now included in different families (respectively, Macrothelidae and Atracidae).

Because of its morphology and funnel-like web, Macrothele calpeiana was included in the same family as the dreaded Sydney funnel-web (Atrax robustus), but this relationship has been disproved by more recent studies

Although Macrothelidae and Atracidae are related, they are not as closely related as they were assumed to be.
More importantly, Macrothelidae venom lacks most of the very harmful (to primates) toxins found in Atrax robustus' venom.
Although M. calpeiana's bite, because of its size and its large fangs, is more than likely to be quite painful, this species is not considered dangerous, despite what outdated information sometimes says. Unfortunately, in terms of bites, there's not much to work with: despite its relatively frequent contacts with people, there is no confirmed record of a human envenomation by Macrothele calpeiana.
A relative, Macrothele gigas, from Southeast Asia (NOT a common stowaway in plants!), is considered medically significant and potentially dangerous, but this is also largely based on its long-assumed (and now disproved) relation with Atrax.
The very rare confirmed bite cases by Macrothele gigas, although they displayed systemic symptoms, were actually not life-threatening, or even very severe; it is also important to specify that this species is about twice as big as M. calpeiana, and can therefore inject much larger amounts of venom.

The "deadly tarantulas in the house plant" story is therefore a complete myth, and, while actual events and spiders share uncanny similarities with the legend, no one's life was in any danger in these situations.

 

3. The Red Spot

It's arguably the most disturbing of the three, which is probably why it is also one of the most popular and widespread, despite also being the most far-fetched.
You've heard that story before, you may have believed it, and maybe it even "happened" to one of your loved ones: someone finds a pimple on their skin, which, instead of healing over the course of a few days, gets bigger and bigger, and eventually turns out to be a spider egg mass. Depending on the (many) versions of the story, the eggs are either discovered and surgically removed on time, or hatch, the spiders coming out in a more or less gruesome way.
The earlier versions of the story take place in Europe or North America, and commonly include a "foreign threat" trope, as it is often told that the victim noticed the "pimple" after or during a trip to a tropical part of the world.
More recently, the tale has travelled and globalised thanks to the Internet, and can be stumbled upon almost anywhere, often popping up in comment sections on social media.

While that urban myth has been around since at least the 1970s, it was brought to posterity by the writer and folklorist Jan Brunvand under the title "the Spider Bite" in his 1988 book The Mexican Pet: More New Urban Legends and some Old Favorites, and to fame, under the title "The Red Spot", in 1991, by Alvin Schwartz in the third opus of his cult classic Scary Stories to tell in the Dark series, Scary Stories 3: More Tales to chill your bones.

Stephen Gammel's wonderfully creepy illustration for Alvin Schwartz's story The Red spot, in Scary Stories 3: More Tales to Chill your Bones

Despite being, therefore, a fairly old and very notorious urban legend, i.e. an entirely made-up work of fiction whose purpose is to scare and entertain, it is still largely passed on by people who sincerely believe in it. Many actually think spiders not only can, but frequently do lay eggs under human skin. 

Interestingly, there is actually no trace of that phenomenon in medical manuals, and no evidence of it from any serious source, nor any convincing photograph on the internet. There's a simple reason why: it cannot happen, not even under the most exceptional circumstances, not even in some remote corner of the Amazon rainforest or the Australian Outback.
It is anatomically impossible for a spider to lay eggs under the surface of the skin, be it a human's or a fruit's skin (no, spiders do not lay eggs inside bananas, or cacti, either).
Spider eggs come out of an opening placed on the ventral side of their abdomen, along a fold called the epigastric furrow. This opening, and its surroundings, are completely devoid of any piercing organ, or anything that would allow the spider to deposit its clutch inside or under a substrate (in other words, an ovipositor). 

Spider eggs come out of an opening at the epigastric fold. Note the absence of anything in that area (or anywhere else) that would allow the animal to pierce a substrate and deposit its eggs in it.

Eggs are laid as a mass, stuck together with a sticky substance, not one by one; and they are immediately wrapped together in a protective egg sac made of silk, which is then hung onto a web, or stuck onto a hard, steady surface.

In many aspects, spiders are a hugely diverse group, but they are extremely conservative regarding the evolution of their egg-laying apparatus and behaviour: they all build egg sacs, even those that only lay one or two eggs at a time. Among the currently 52000+ described species, no exception is known. Even the species which do not make webs still build egg sacs for their clutches, and, because it is so widespread, egg sac production is regarded as the original use of silk in spiders.

All spiders build silken sacs for their eggs; they can be extremely simple or remarkably complex, such as the impressive cocoon of this Cape rain spider (Palystes castaneus)

 

It would also be impossible for a spider to stuff its egg mass into a wound caused by its bite; the puncture wounds left by the fangs are tiny, and even pushing a single egg into it would crush it, let alone an entire egg mass. It would not, either, be able to cut the flesh with its fangs and enlarge a wound in order to insert an egg sac: spider fangs are piercing needles, not cutting blades!

In addition to that, all known spiders are predatory or omnivorous (some include dead invertebrates and plant matters in their diet, and one species, Bagheera kiplingi, is even mainly vegetarian), since their very first meal. There is no known blood-sucking or parasitic spider species, of humans or any other animal.

Of course, one can still argue that we don't know every spider species on earth and their behaviours, and that an exception could very well exist out there; and that would be a good point.
However, a "spider" adapted to lay eggs under human skin would need an egg-laying apparatus and behavioural adaptations so radically different from any other spider we know, that it would either not be considered a spider, or challenge the very idea of what defines a spider, as the production of silk by the spinnerets, whose primary function is assumed to be making egg sacs, is regarded as one of their main synapomorphies (the trademark features that define the group).

More importantly, there is no valid explanation as to how and why this supposedly parasitic spider, whose existence is "attested" by countless alleged "observations" by laypeople, has so far managed to completely elude the attention of arachnologists, physicians, or just anyone, scientist or not, who would be willing to rigorously document and photograph this peculiar species!

The closest thing to a spider that can lay eggs under human skin is the scabies mite, Sarcoptes scabiei. This microscopic mite burrows under the skin of humans and other mammals, causing itchy and distinctive rashes. Scabies is a contagious disease, which can be easily spread through close physical contact.
It is quite likely that this urban legend may have been fuelled (or even created) by misconceptions about the scabies mite, from medical professionals explaining what scabies is to their patients by wrongly describing it as "like a tiny spider" or "a close relative of spiders", and/or from patients misunderstanding or oversimplifying their explanations. However, Sarcoptes scabiei is definitely not a spider, nor is it "almost like a spider".
Like spiders, it is part of the class Arachnida, but belongs in a completely different branch of the Arachnid lineage, the superorder Parasitiformes.
It is a mite, not a spider, and describing the scabies mite as "like a tiny spider" is about as accurate as describing a platypus as "like a tiny, furry, duck-billed human"!

The microscopic (actual size: 0.3-0.45 mm) scabies mite, Sarcoptes scabiei. Note that, although distantly related to spiders, this animal is radically different from them (image source)

However, don't be too quick to assume that anyone claiming they have seen with their own eyes a doctor "pulling an egg/an egg sac from under their skin" is a liar. They may be sincere, and may have actually seen the doctor extracting a sac-like thing full of eggs from their skin!

What they saw, though, was not a spider egg sac at all, nor was it even from an Arachnid. It was an insect, more specifically a very strange species of flea, whose appearance and life cycle shows uncanny similarities with what is described in the myths: Tunga penetrans, the sand flea or chigger flea.
The sand flea (not to be confused with many types of unrelated marine crustaceans also improperly called "sand fleas", or with what is known as a "chigger" in North America, actually a biting mite) has a different lifestyle from its more typical cousins such as cat or dog fleas.
Contrary to most types of fleas, which remain on the surface of their host's skin, biting from time to time to feed, Tunga penetrans lies in wait in loose sandy or muddy ground, for a warm-blooded animal (such as a farm animal, a wild mammal or a human) to pass by. When a suitable host comes by, the tiny (1 mm) adult fleas climb on its feet and bite, to feed on its blood.
While adult males immediately return to the environment once fed, mated females do not stop there: they latch on and claw their way in, burrowing into the skin. Because the flea is still tiny at this stage, that process is normally quite painless.
After a few days of feeding continuously on their host's blood, the female flea's body swells up so much it becomes unrecognisable: the membrane in between the abdomen segments stretches and inflates, and its body turns into a huge, white, bloated sac, filled with blood and eggs.
Fully engorged, the female flea is ten times larger than before feeding, its abdomen reaching a centimetre in diameter.

A partially engorged sand flea, Tunga penetrans (under its older name, Sarcopsylla penetrans)

From the outside, an engorged female sand flea under the skin looks like an irritated white boil with a tiny dark spot in the middle (the dark spot is the terminal segments of the abdomen, which stick out of the skin and allows the flea to breathe and release its eggs). After 8 days, the flea starts laying eggs, which fall off the host and drop onto the soil, where they will hatch into larvae. A female sand flea will lay about a hundred eggs over a two-weeks period, after which it dies and is eventually sloughed off by the host.
Tungiasis (parasitic infection by Tunga penetrans) isn't really dangerous in itself, but the lesions caused by the fleas are painful and prone to secondary bacterial infection, particularly if there's many of them. The most common course of treatment is surgical extraction  of the insects with a sterile needle. Therefore, situations where people have gross sac-like things full of eggs pulled from their skin do indeed happen. They have, however, nothing to do with spiders.
Chigger fleas are found in tropical and subtropical regions of the world. They are mainly prevalent in Central and South America, the Caribbean and in sub-Saharan Africa, and most commonly found around beaches, sandy riverbanks and farmland, particularly in places where farm or stray animals such as dogs, pigs or cattle are abundant. As they attack the body parts in direct contact with the ground (almost always the feet), the best way to prevent this unpleasant experience is to avoid walking in such places with bare feet. 

Because of sand fleas, walking with bare feet or digging with bare hands in the sand in tropical and subtropical areas is not advised, particularly if there's lots of free-roaming animals such as dogs or pigs around

The sand flea has a lot in common with the fictional parasitic spider; it is more than likely that real cases of tungiasis have inspired this urban myth, either through people misinterpreting what they saw or what was explained to them by the doctors, or willingly altering the story to make it scarier, by replacing the tiny flea with a larger and more spectacular spider.

Unfortunately, when it comes to spiders, myths are more common than facts; with these three urban legends, we barely scratched the surface of the many false, often downright silly, rumours about these animals. There is more than enough material out there for another, or even ten, articles like this one.
These urban legends are the perfect demonstration that what makes a false fact efficient is its ability to shock, scare and durably imprint the mind, rather than its believability. To anyone who isn't afraid of spiders, and even more to someone who knows a thing or two about them, these stories sound simply ridiculous, and obviously fake.
However, to an (even mildly) arachnophobe, they are terrifying; silly or not, they'll make a nest in their mind and stay here, half-believed, feeding the fear, simply because of the "what if?" factor. It will take as little as someone else, particularly if it's a trusted figure such as a relative or a doctor, sharing the same story, to turn that half-belief into a firm conviction of truthfulness.
That's why it is critically important to debunk these stories as often as necessary, because they don't just get spiders killed for no reason; they harm people too, and make some lives more difficult.
It's also primordial to keep in mind that the majority of what we hear and read about spiders, not just these three examples, is complete bullshit.
When coming across a scary spider story, one should thus always assume, unless there is factual confirmation by an arachnologist (not just any "expert"), that it never happened, or that it is, at least, wildly distorted and exaggerated.⏹

 

 

Addendum Dec. 10, 2023: No, spiders still don't lay eggs under human skin! 

If you've read the news recently, you may think the third part of this article might be outdated, or at least too categorical in its conclusions. Indeed, an article published on Nov. 28, 2023, claimed a spider laid eggs in a British man's big toe in Marseille, France, during a cruise.
Sure, silly horror tales like this are a common sight on the pages of base tabloids like the Sun or the Daily Mail, which are notorious for not caring much about how true a story is as long as it's sensational. However, in that case, the original source was no mere rag: it was the BBC, the most consulted news outlet in the United Kingdom.

The original cover and title of the BBC article, as released on Nov.28. The picture is not a photo of the alleged culprit, but a stock image of a Phoneutria sp., not even a wolf spider.

The spider was allegedly identified by the ship's doctor (someone who is not trained or qualified to identify a spider, even with a specimen at hand) as a Peruvian wolf spider (!) accidentally transported to France (!!). As always with those stories, the animal was never seen or felt (but somehow, the medical staff could identify it as a wolf spider, and a Peruvian one with that!), not even when it supposedly bit the man and laid eggs in the wound. The "victim" initially thought it was just a simple blister caused by new shoes. As the tale went, it's only when the toe became heavily infected that the man sought medical attention, and was horrified to discover spider eggs in the pus drained from the wound. Because a good story wouldn't stop there, the ship's medical staff left one egg (of course!) in the wound, which hatched after he got back to England, where the spiderling, which "had started eating his way out", was discovered and "surgically extracted".

You probably don't have to be an arachnologist to find this story hard to believe. Everything in it is incredibly far-fetched, and, more importantly, bears the hallmarks of a textbook urban legend:
- There's multiple layers of the "foreign threat" trope, as the spider itself allegedly comes from a remote and distant land (which makes the claims conveniently unverifiable: who, besides a few biologists, knows what kind of spiders hide in the Peruvian Amazon?), attacks the man while he is enjoying vacation in a foreign country (France), and one spider left in the toe gets unwittingly brought back to the "safe, clean homeland"!
- The ability of the "knowledgeable authorities", in that case, the ship's medical staff (when your average doctor doesn't know much more about local spiders, let alone Peruvian ones, than most laypeople!), to instantly and accurately identify the exact nature of the threat, even though it's something wildly exotic and never seen before, is another common urban myth cliché.
- Finally, in addition to the "foreign threat", it features another major urban tale archetype (found in "The exploding cactus", "the red spot" and many more): the innocuous-looking, ordinary element (in that case, a blister) that gets initially ignored, but progressively turns out to be something much more disturbing.

Thus, even to someone who has never heard of the "Red Spot" urban legend specifically, there are many elements that a person familiar with urban myths and fabricated stories (which a journalist should be, as being able to tell actual news from a hoax should be a basic and fundamental requirement for the job) should find highly suspicious. 

Of course, sometimes, actual events are so strange that they can sound like a tall tale, and still be true. However, the more outlandish the claims, the more robust the elements of proof need to be.
In that case, the proof is entirely non-existent: the only photographs illustrating the original article are an image of a rather typical-looking, albeit badly infected toe, with no visible trace of spiders, and a stock photo (from Getty Images) of a male Phoneutria sp., a genus that is not even in the right family (the alleged culprit was a wolf spider, family Lycosidae, while Phoneutria belongs in the family Ctenidae). Of the allegedly extracted eggs and spiderling, there is none.
Two different medical teams in two different countries reportedly performed surgical removal of eggs and spiders on that toe, and neither of them even thought about documenting their highly unusual findings!?
Speaking of the medical teams, neither of the two were contacted and interrogated to confirm the story, nor was an arachnologist asked about its plausibility.
While it was not explicit in the original article, it was quite clear that the only source was the alleged "victim", with nothing and no one to back his claims.

Understandably, the release elicited vocal and immediate criticism and responses, particularly from arachnologists, who pointed out that the story was a famous, obvious, and biologically impossible, urban tale. The next day, the BBC had heavily amended their article: they made it much clearer that the whole thing was solely based on the unproven, unconfirmed allegations of one man, removed the spider stock photo, and included the comments of a professional arachnologist, Dr. Sara Goodacre, and of the British Arachnological Society, who both challenged the plausibility of the tale.

The next day, the tone and contents of the BBC article were radically amended

 

Unfortunately, the harm was already done. The people who got fooled and scared by the original version are not likely to go back to the article and read the new, corrected one. In addition to that, less reputable newspapers had immediately caught wind of it and shared the "news" on their own platforms, while not being as scrupulous about the disclaimer...

The thing is, while the BBC is not exempt from occasionally indulging in "quick and dirty journalism", it is widely perceived as a reliable news outlet. More importantly, it is the most consulted in the UK, and, internationally, the most famous British media. Sadly, it means that when they release such a ridiculous, obviously made-up story without even the most basic verification, it has a much greater impact and coverage that when it comes from a mere tabloid, and the lies spread much faster and further.

Just because it made it to the papers (even when it's one with a fairly solid reputation) doesn't mean a story is true. "The Red Spot", or, in that case, "the Infected Toe", is still an urban legend.
Wolf spiders carry their egg sacs with them, attached to their spinnerets; when they hatch, the spiderlings crawl on their mom's back and stay there until they can fend for themselves. They don't abandon their eggs, and certainly not in an open wound. That ridiculous tale is just a web of lies: spiders, even those from Peru, don't lay eggs under human skin.

All female wolf spiders guard their egg sacs, carrying it with them, attached to the spinnerets, when they move around. Once they hatch, the babies climb on their mom's back and depend on her until they're big enough to fend for themselves. They don't abandon their eggs, and certainly not under human skin.

 

Lingo:

¹Factoid: A piece of unverified (and more often than not, false) information that gets accepted and passed on as fact, simply because it is widespread and has appeared in one or several media. Recently, the term "factoid" has been incorrectly used to describe "a short, interesting tidbit of true fact", but the term "factlet" should be preferred for the latter, as an important aspect of the original definition of the factoid is its untrue, or at least dubious, nature.
Example: "Oil is made from dinosaurs" is a strangely widespread, but completely false factoid. Oil (and other fossil fuels) does not come from dinosaur fossils, but from plankton deposited in low-oxygen environments (the low oxygen prevented complete degradation of organic matter, allowing it to become buried under sediment and slowly "cooked" by the pressure and heat of deep sedimentary rocks). The factoid comes from the oil firm Sinclair Oil Corporation, whose marketing relied heavily on the image of dinosaurs (arguably more charismatic than microscopic algae) between the 1930s and the 1960s, prompting an association between fossil fuel and dinosaurs in the public's mind, particularly in the USA (as Sainclair is an American company).

Except when the source is explicitly cited, the images illustrating this blog are mine and are not free to use without permission.

References are integrated in the text of the article; the words in blue are clickable and will redirect you to the sources of the information.