I’m going to go out on a limb and say that you’ve probably seen a spider before. Well, that is, unless you’ve been living your entire Earthly existence on the barren, ice-blasted wastes of the Antarctic interior…in which case, I don’t have conversations with murderous, shape-shifting aliens, kthnxbai. Spiders comprise the largest and most successful order of arachnids, with nearly 46,000 species living everywhere from rainforest canopies, to scorching desert sands, to pitch black caverns that wind miles underneath the ground. They are exceedingly varied in their lifestyles and habits. Some can glide like a frisbee from high up in trees. Some slink along the surface of standing water, and nab minnows like some kind of mini, eight-legged, catfish noodlin’ Jesus of Nazareth. Some specialize in the most dangerous prey…other spiders…and net them with a toxin-laced phlegm that they spray from their mouthparts.

Yes, with all their diversity and ubiquitousness in both ecological and human cultural settings, spiders are unquestionably the flagship arachnid group (although many other fascinating orders exist; see the first entry in my lesser-known arachnids series for information on the Class Arachnida in general). Whether we love them or hate them, spiders, as a group, are familiar to us, and many people are aware that spiders come in a huge range of shapes and sizes. For example, it is no secret that black widow spiders (various Lactrodectus species) are among the more dangerously venomous species in North America….or, that the fuzzy, hamster-sized tarantulas (family Theraphosidae) are the biggest spiders on Earth. But what is much less widely known is that far more than size and venom differ between tarantulas and black widows.

While it’s perhaps instinctual to think of spiders as existing in a big monolith of vague “spideriness” with minor tweaks on a common, eight-legged theme, spiders actually divide up into distinct groups with important biological differences, the result of deep evolutionary rifts that stretch back hundreds of millions of years. The truth is that there are several very distinct branches of the spider family tree.

All spiders belong to the same taxonomic order: Araneae. It’s easiest to think of this grouping initially breaking down into two main clusters (suborders). One of these is an early offshoot of the spider lineage, represented today by a single family (Liphistiidae) and only 80-some poorly understood species. This suborder, Mesothelae, contains holdouts from eons ago, a time when they enjoyed much greater diversity. These are the living fossils of the spider world, and retain a lot of “primitive” features that were present in the first spiders, like hints of segmentation on their abdomens, and poorly-developed venom glands. Mesothele spiders (named for the position of their spinnerets (“thelae”) in the middle (“meso”) of the underside of their abdomen, rather than at the end like in other spiders) are found only in East and Southeast Asia, and generally lead secretive lives as burrow-dwelling ambush predators. All other living spider species, well over 99% of them, belong to the other of the two suborders; the Opisthothelae.

Suborder Opisthothelae breaks down into two smaller branches (“infraorders): Araneomorphae and Mygalomorphae. The overwhelming majority (perhaps all) of the spiders you’ll encounter in a lifetime belong to the first group; about 90-92% of all known spider species are araneomorphs. Every delicate, suspended spider web that you’ve walked face first into, and every cotton candy-like cobweb you’ve brushed away during spring cleaning, came from an araneomorph spider. Roughly 40,000 species strong, these are the spiders we are the most well-acquainted with, from your standard, garden orb weaver, patiently hovering above your tomato plants, to the carefully camouflaged crab spider waiting to pounce on any pollinator visitors to the weedy goldenrods bordering your lawn. Some of the more charismatic araneomorph species have achieved Internet virality, like the now relatively famous Australian peacock spider, and the adorable and elaborate courtship boogie that the males of the genus whip out to get some steamy spider tail.

Nothing drops the spider panties faster than the ol’ Air Traffic Controller Clown on Amphetamines routine

But, while araneomorph spiders are a successful group, they are not alone in the opisthothele world. Another 8-10% or so of the 46,000 spider species belong to the other opisthothele infraorder; the Mygalomorphae. The members of this infraorder (the mygalomorph spiders) are the subject of this blog entry series. I’ve pointed them out on the tree below, which illustrates some of the evolutionary relationships within spiders, and between spiders and their closest relatives.

Mygalomorph spiders differ from their araneomorph cousins in a number of ways that profoundly impact their biology.

For one, their fangs (the “chelicerae” mouthparts found in all arachnids) are oriented parallel to one another, while the fangs of araneomorph spiders are crossed. Make “air quotes” with your pointer and middle fingers. This approximates the biting direction of mygalomorph spider fangs. This is what’s known as having an “orthognath” bite (“ortho-” meaning “straight”, and “-gnath” meaning “jaw”). In contrast, if you put your pointer finger and thumb together, this is the crossed orientation seen in the araneomorph spiders. When it comes to plunging those sharp, venom-loaded babies into a luckless victim, mygalomorph spiders are “stabbers” and araneomorph spiders are “pinchers.” Mygalomorphs bite like a rattlesnake. Araneomorphs bite like the hand of an overzealous St. Patrick’s Day celebrator who just noticed you weren’t wearing green today.

Mygalomorph spiders are also generally shit at making webs. Unlike araneomorph spiders, they don’t have the ability to make “piriform” silk, a type of spider silk that is superbly sticky and is very useful as a glue for joining different silk strands together, or for getting silk to adhere to random surfaces. Piriform silk is pretty crucial for making the big, complex, aerial, spoke-and-wheel bug-entangling booby traps that are so commonly associated with spiders. Mygalomorph spiders can still make multiple varieties of silk, but their use is much more limited. Partially because of this inability to perch high up in the air in a nearly-invisible Glue Net of Death, mygalomorphs tend to gravitate towards ground-based lifestyles, with many species existing as ambush predators hiding out in web-lined burrows and waiting patiently for an ill-fated prey item to stumble across a strategically placed trip line (or just get close enough to send down some mouth-watering vibrations through the soil). While some species of mygalomorph will spend their nights prowling the forest or desert floor for grub, most species spend the bulk of their lives camping out Saddam Hussein style; shuttered in the back end of a dank hole in the dirt. If Peter Parker had been bitten by a radioactive mygalomorph spider, his main superpower would be the ability to sit motionless for days in a pitch black cavern while letting New York City burn.

“Spiderman, spiderman
Does whatever a spider can
Underground, all the time
Infrequently fights crime
Fuck off!
You’re bothering the Spiderman
Is he strong?
Listen bro,
Probably, but he’s sleeping though
Can he swing from a thread?
Nope.”

Mygalomorphs have adapted to this largely terrestrial lifestyle and lack of dependence on webs by generally being large, heavy-bodied, powerful spiders. Many species have biiiiiig honkin’ fangs…all the better to pin down prey that, in the absence of immobilizing webbing, are very mobile and very upset. The infraorder actually contains the largest spiders in the world, and one group of mygalomorph spiders in particular, the tarantulas (family Theraphosidae), are well-known for their size. Even the name “mygalomorph” is in reference to the group’s propensity to evolve big, furry, hefty spiders; “mygalo-” comes from the Greek for “shrew” (mugale), where “morpho” means “form/shape”…mygalomorph = shaped like a shrew.

Mygalomorph spiders also grow and mature much more slowly than araneomorph spiders. Some mygalomorphs can take a couple years to reach reproductive age…longer than the entire lifespan of a great many araneomorph spiders. Mygalomorphs generally also have remarkable longevity, potentially living for as long as 25 or 30 years. Their comparative late blooming makes mygalomorphs a bit more susceptible to extinction than araneomorphs….something also exacerbated by the mygalos being huge homebodies, which makes their geographic ranges small and clustered.

Basically, if araneomorph spiders are the Cro-Magnons of the spider world, then mygalomorphs are the Neanderthals; stoutly built, strong as hell, and fond of caves.

As mentioned before, tarantulas are far and away the most familiar group of mygalomorphs, but the greater diversity of the infraorder is full of bizarre and lesser known spiders, some of which are little like their famous, humongous cousins. Some of the closest relatives to tarantulas live in environments completely different from the deserts and tropical rainforests associated with the world’s largest spiders. This series will shed some light on some of these mygalomorph spiders. I’ve broken these other mygalomorphs down into three main groups, one for each entry in the series: “tricky assassins” (crafty ambush predators), “toxic biters” (the most venomous mygalomorphs), and “tiny hunters” (miniature and unique species rarely seen by humans). This first entry in the series will focus on the “tricky assassins”, mygalomorphs that have evolved a number of traits and behaviors that make them invisible, subterranean harbingers of death upon all that are small.

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It’s early August in northeastern Georgia, at eleven in the morning, and it’s already hot. The air sits tepid and dank, like air above a piping hot bath. This time of year in this arm of the Chattahoochee National Forest, the heat and humidity come early in the day, and the weak breeze is barely enough to disturb the hickory and red oak leaves above. For a single precious moment, the wind picks up, whistling up a thickly-treed trough cut by the Chattooga River as it flows south off the Appalachian highlands. You, a swamp cicada who just finished their scratchy, morning aria from an oak branch overhead, are surprised by the gust, and your grip fails you, sending you plummeting to the undergrowth thirty feet below.

Mildly irritated by the fall, you struggle and worm your way back onto your six legs, adjusting yourself on a patch of moss near the base of the tree. The ground is nowhere for a large, conspicuous bug as yourself, and you instinctively start to leisurely toddle through sumac and young hawthorn. After gathering the will to scale a rotten, fallen pawpaw fruit, you’ve finally reached the trunk of the oak tree you unceremoniously tumbled from. Slowly you climb, gripping with your six, weary limbs. In your path ahead, you notice a long, thin branch propped up and flush against the tree trunk, extending all the way down through the leaf litter and decomposing twigs to the dirt, and about twice as wide as your body. Your legs move you up and towards the little branch, and as you begin to cross it, you can’t help but stop. It’s soft underneath your feet, pliable; it feels almost hollow underneath, with each movement making it billow wildly like a waterbed. On the surface of this apparently very rotten branch, you are clumsy and can’t seem to get comfortable footing, so you begin to move back to the solid wood of the tree trunk.

Just as you’re about to reach out to the side with your first pair of legs, you feel two hard, massive hooks, each nearly half the length of your body, erupt from underneath and impale your thorax with catastrophic force. Nearly instantaneously, you are then yanked downwards so hard that your legs are splayed out at your sides, entirely useless in propping your body back up. Panic catches fire within you, and every limb and antennae is thrashing, but the strength of what has you seems boundless…and you again are tugged by your belly. One of the thick, sharp hooks remains embedded in your exoskeleton, and you can feel your body cavity filling rapidly with a warm, tingly, seeping tide. The other has gone all the way through you, sticking out of your back like a toothpick through a cube of cheese. Another cruel jerk from below pins this hook against your fragile body, folding your pitiful, crunchy physique in half, securing you against the tree trunk like a staple affixing a flier to a utility pole. You can feel the hooks working independently now, shifting, gnawing, tugging and sending agony through the whole of you. The venom that flooded into you from the hooks has ceased your ability to fight, and all of your legs are limp and your antennae bruised and lethargic…but it has given you no relief from the pain. You can hear the movements of four pairs of legs straining below and behind you. Flexing. Scraping. The hooks clench downwards again, and your consciousness flickers as your body creases into the shape of a cicada taco. For a moment, in your arched, contorted position, your head articulates up over your crushed mid-section, allowing you to gaze back at your own wings through your compound eyes. You’d never actually seen them before. Great, tapered sheets of translucent bubblewrap. You had no idea they were so beautiful.

The hooks pull one more time, stronger than all the others, and you are dragged down into the blackness of the silk sleeve you mistook for a withered branch, succumbing to the callous, gnashing fangs of your murderer: a large, female red-legged purseweb spider (Sphodros rufipes).

………………………………………………………………………………………………………………………………..

Purseweb spiders are mygalomorphs in the family Atypidae. They are sometimes referred to as “atypical tarantulas”, although they aren’t particularly closely related to true tarantulas; the name honestly makes about as much sense as calling a walrus an “atypical cat.” The purseweb spider family contains only three genera, but about forty different species; they are found in diverse environments in Mexico, the continental U.S., across much of Eurasia (but not in northern Siberia, the Arabian Peninsula, or a large portion of Indonesia), and mainland Africa. Some Eurasian species live at very high latitudes (I’m talking Scandinavia here) and in consistently cold, damp climates, a far cry from the habitat preferences of the tarantulas they share a name with. They are squat, heavily-constructed spiders, and while they aren’t as big as true tarantulas, the females of some species can have bodies too big to fit neatly on a U.S. quarter coin….a respectable size for any spider. I note the females specifically, because in this family (as with spiders in general), the females are the ones with all the heft; females are generally twice as long as their masculine counterparts, and easily four or five times the mass. Males tend to have dinky, shrunken abdomens that make their legs look especially long and gangly, and gives their front end a weird, inflated, “bobblehead” appearance. The boys make up for it though. Mature males are often brightly colored (in contrast to the black or brown lady purseweb spiders), and during the breeding season, can be occasionally seen wandering out in more open areas seeking the lairs of females. One of these, the red-legged purseweb spider (in the above story), a native of forested areas in the southeastern and eastern U.S., is so named for the male’s legs, which are as red as the Carolina hot dogs found in the heart of its geographic range. No she-spider can resist the lust that lurches to life from laying eight beady eyes on a set of sunburned striders.

Dem gams tho

The most “atypical” thing about purseweb spiders are the webs they make. Other mygalomorphs are content to have a dirt burrow wallpapered with a few layers of webbing, to create a stringy tunnel positioned underneath a rotting log, or a debris-shrouded crevice in a pile of rocks. In these cases, the inside of the burrow or funnel-web is accessed by simply going down the opening, and both spider (and potential prey) enter through a well-defined foyer. But when purseweb spiders draft the blueprints for their secluded homes, doors, windows, or any points of entry are scrapped. Most species make a two part cylindrical web, where the majority lines a burrow that goes vertically down into the dirt by six inches to a foot. A shorter section of web extends out onto the surface, forming a hollow sausage with the other end closed off. This part can lay flat along the ground, or it can be propped up and fastened against a log or tree trunk at an angle. The above ground section of web is commonly camouflaged with leaf debris and dirt to look like part of the vegetative landscape. Insects and other small arthropods clamber over the exposed outer surface of the web, oblivious to the hungry fucking spider cocooned inside like the world’s worst stocking stuffer, patiently waiting in the subterranean section for the faintest hit of vibration traveling down from the surface. The hollowed out silk sausage sitting on the surface betrays the presence of any beetle or centipede or whatever that makes the mistake of walking across it, as the purseweb spider can sense the strain on the inside of the tubular sheath under the ground. The whole web structure is basically shaped like a half-buried condom, but, you know, with a jumbo-fanged fearbeast tucked snugly inside.

Pictured: something that should be never be anywhere near a penis

See that pair of “fuck no”-size fangs up there? Those puppies have a very specific role to play. Purseweb spiders have a couple goddamn billhooks coming out their faces because they are the only body part used to capture prey. Once the purseweb spider “hears” the dinner bell ringing upstairs, it sprints along the inside of its sack-shaped contraption, positioning itself upside down and right underneath its naive victim, with nothing between the two of them but a silk shell as thin as a tomato skin. The spider then stabs upwards through the wall of the cocoon with its fangs, coming at its prey like a burrito that bites back.

As some burritos are wont to do.

This subterranean bear trap completely takes the prey by surprise. The fangs tightly grip the poor, tiny soul, and within a few moments, the spider backs down the silken tube, helpless supper in tow, leaving a hole in the top of the tube. This whole process can be seen in real time in the video embedded below, where a purseweb spider hooks a cricket from underneath and pulls it down through the wall of the silken envelope like a horror film jump scare scene IRL. You can’t see the fangs spring out of the World’s Most Dangerous Egg Roll down there at the 0:03 second mark; they move much too fast for the human eye to even register. But you can clearly see the effect on the cricket at that very moment, because it looks like it was just speared by an invisible push pin.

At the end of the video, the purseweb spider returns to the scene of the crime and stitches together the tear in the silk tube, making it nice and ready for course number two.

The “stealth sock” method of ambush predation is unique to purseweb spiders, and another, different strategy is more widespread among mygalomorph spiders; the use of “trap door” burrows. The spiders that use carefully hidden trapdoor entrances to their burrows to bushwhack ignorant passersby are collectively known as “trapdoor spiders”, although the term itself is a bit problematic. Firstly, the hunting method is apparently quite popular among mygalomorphs, as seven out of the fifteen mygalomorph families are made up of “trapdoor spiders.” All of these families don’t belong to a natural, evolutionary group (as in, trapdoor use appears to have evolved independently, in multiple separate lineages). So, the term “trapdoor spider” just describes a general lifestyle, and doesn’t reflect the evolutionary origins of a unified trapdoor spider group. There are subtle differences among all these distantly-related families, both in anatomy and trapdoor style, with each lineage coming up with a different means of accomplishing the same goal: popping up out of the ground like Little Miss Muffett’s least favorite version of Whack-a-Mole.

One group of trapdoor spiders are the “folding trapdoor spiders” (family Antrodiaetidae). This is a pretty small family, with only thirty species in two genera (Aliatypus and Antrodiaetus), and it’s members are only found in the Western and Northeastern U.S., British Columbia, and Japan. Folding trapdoor spiders appear to be the closest relatives of purseweb spiders, and are only somewhat distant relatives to all the other “trapdoor spider” families. Most species are small to medium-sized by mygalomorph standards, typically under an inch or so long. They get their name from a style of door used to block the entrances to many species’ burrows. The “folding door” is made out of silk instead of hard materials (as in other trapdoor spider families), and is a mobile sheet of silk that is pulled back across the burrow’s opening. Technically, it’s less a door and more of a blackout curtain. Other members of the family have flat, dirt discs that have a “hinge” held together with a strategically-placed piece of silk.

A particularly cool member of the folding trapdoor spider family is the California turret spider (Antrodiaetus riversi), native to damp, wooded areas in Northern California. These spiders build burrows like any other trapdoor spider, but also extend the opening of the burrow above the surface, making a cone of dirt clods and conifer needles that forms a little pimple on the ground, with a caldera opening in the top. When actively hunting (usually at night), these “turrets” have their hatches pulled open, and the turret spider waits right inside the lip of the entrance for anything to come within pouncing range. The setup is a bit like a miniature papier-mâché volcano model, except instead of spewing forth a vinegar and baking soda froth, this one erupts fucking spiders.

A helicopter shot of the summit of Mt. St. Hell-no

In some places, the density of turret spiders can be incredibly high, and sections of the ground look like someone shrunk a bunch of prairie dog mounds, with a rash of raised bumps pockmarking the forest floor. Needless to say, any insect that strays into these minefields isn’t likely to fair well. A turret spider locked in hunting mode is incredibly sensitive to any movement near the rim of its burrow opening, so much so that humans can instigate a pouncing response by giving the turret just the most delicate of tickles, in an amusing (if a bit dickish) game of Ding Dong Ditch:

Turret spiders don’t ever really leave their burrows unless it’s to find a mate (and then, it’s really only the males the head out into the big scary world). Turret spiders, even more than a lot of other mygalomorphs, tend to stay in one place…so much so, we’re finding out, that the spiders can have many, many generations hanging out in their hometown for their entire lives. Once these spiders set down roots, they don’t tend to leave…ever. A consequence of this clustering of populations, something we can see their DNA. Since turret spiders don’t really move, it’s really easy for even minimally physically isolated populations to become genetically distinct from other populations. There’s even some genetic evidence to suggest that the California turret spider is actually many species, each existing in tiny territories scattered across Northern California.

A second group of “trapdoor spiders” are the “tree trapdoor spiders” (family Migidae). Tree trapdoor spiders are found on the southern continents of old Gondwana: South America, Africa/Madagascar, New Zealand, and Australia. Their ranges on these continents tend to be in more temperate and subtropical areas, and areas with lots of moisture (unsurprisingly, tree trapdoor spiders aren’t found in the Sahara or in the powder dry interior of the Australian continent). Most of the nearly 100 species in the family build some form of nest within the bark of a tree with a trapdoor lid. Some of these nests are short and pocket-shaped, with just enough room for the spider inside. Many migid spiders are small in size compared to other mygalomorphs, and given their tree-dwelling tendencies, they are rarely encountered by humans, and its possible there are many more undiscovered species.

Seeing one in the open like this? Migid-aboutit.

No member of the Migidae highlights just how little we know about these spiders like the tingle trapdoor spider (Moggridgea tingle). The common name comes from the apparent preferred habitat for the species: the bark of red tingle trees (red tingle (Eucalyptus jacksonii) is a large species of eucalyptus tree found only in southwestern Australia). The spider was only discovered by science in the 90s, and given its rarity, and small geographic range limited to pockets of tingle forest in the mountains south of Perth, it’s generally assumed to be already vulnerable to extinction. Many other tree trapdoor species found across the Southern Hemisphere are known only from incredibly small geographic regions, and it’s possible that this group, completely dependent on wet forests, are as old as the ancient pockets of trees that persist in the forgotten corners of former Gondwana.

The last group of trapdoor spiders this entry will address are the “true” trapdoor spiders (family Ctenizidae). There are more than 100 species in this family, and they are found all over the globe, from the warmer areas of the Americas, to Australia, East Asia, and parts of the Mediterranean and Southern Africa. The only real distinguishing physical feature in this family are little backward facing barbs on the mouthparts that aid in actually excavating out the burrow. Many species in this family also use a heavy, cork-like trapdoor with a silk hinge. Some ctenizid trapdoor spiders can be pretty bulky, even by mygalomorph standards, so due to their sheer width, the burrows can be hard to miss if the trapdoor is opened up. An exposed burrow for a particularly large individual in this family can look like a little, uncovered manhole.

Hey! That’s a safety hazard!

While many spiders in this family pretty closely adhere to the standard trapdoor spider way of life, some ctenizid spiders have evolved some bizarre traits. Take, for instance, the spiders in the genus Cyclocosmia. Trapdoor spiders are by no means at the top of the food chain, and most trapdoor spiders rely on the covert nature of their secret passages to their burrows as de facto protection against predators. But Cyclocosmia trapdoor spiders have another defensive tool just in case their front door is breached. When pursued by an attacker, it turns its face away from the opening of the burrow. It doesn’t have to be in the burrow itself all that far, as long as its rear is facing the assailant. This does the trick, because unlike its flabby-assed relatives, this trapdoor spider is equipped with buns of steel. Well, perhaps not steel; just a flat, armored cap at the end of its abdomen strengthened with rigid rib and spine-like structures. This feature causes the end of the abdomen to appear abruptly cut off, making Cyclocosmia resemble what an acorn would look like after taking a hit of that fear gas shit Scarecrow uses in Batman Begins.

“From little spider-acorns, mighty spider-oaks do grow.”

This “butt plug” (….er…so to speak) creates a nearly impenetrable stop in the mouth of the burrow, its tough surface impervious to harassment from a wide range of predators.

This ass-shield is a likely boon to Cyclocosmia, considering that ctenizid trapdoor spiders are regularly targeted by parasitoid spider wasps. Spider wasps are the real-life equivalent of the xenomorphs from the Alien film franchise; they abduct, paralyze, and have their wriggly larval babies eat the spiders alive…so, you know, there’s that….

Outside of these example groups, there are still other families of so-called “trapdoor spiders”, like the armored trapdoor spiders (family Idiopidae), the wafer trapdoor spiders (family Cyrtaucheniidae), and the brush-footed trapdoor spiders (family Barychelidae). The lie-in-wait ninja hunting method appears to work well for many different lineages of mygalomorph spiders. Without the ability to catch food with silk traps directly, options are surely limited, but purseweb and trapdoor spiders have evolved into accomplished ambush predators, and have guaranteed that no dirt-bound environment is a safe haven for this planet’s innumerable insects.

As ferocious as these species are, in a predatory context, none of them pose any threat to humans, as none of their bites have a medically-significant punch. This is not the case for some other mygalomorph spider families, which harbor some of the most dangerously venomous spiders on the planet. Part 2 in this entry series will explore these “toxic biters” of the mygalomorph world…

Image credits: Introductory image of mygalomorph in threat display, tarantula in burrow, male red-legged purseweb spider, female purseweb spider with fangs exposed, Chipotle sign, California turret spider, turret spider gif originally from this YouTube video, migid spider, trapdoor spider burrow, Cyclocosmia

© Jacob Buehler and “Shit You Didn’t Know About Biology”, 2012-2016. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jacob Buehler and “Shit You Didn’t Know About Biology” with appropriate and specific direction to the original content.