This post is the fifth in an ongoing series on arachnids. Previously, this series addressed whipspiders, hooded tickspiders, pseudoscorpions, and harvestmen. Additional posts on other weird, often overlooked or neglected groups of these creepy crawlies to follow. For a related chelicerate, but as far as science can tell, not an arachnid, see the post on sea spiders.

The solifugid.

This group of fleet-footed arachnids is known by many names across the globe. Wind scorpion. Camel spider. Sun spider. Sun scorpion. Unintelligible screaming and cursing. All of these refer to members of an enigmatic order of arachnids; Solifugae. The name of this order, derived from Latin, means “those that flee from the sun”, an acknowledgement of their habit of chasing shadows in an attempt to stay cool in their predominantly hot, sunny, and arid native habitats. Despite their frequently used common names which identify them as some sort of breed of spider or scorpion, solifugids (a more accurate identifier of the arachnids within the Order Solifugae) are most certainly a distinct, separate animal from either group. They may have the long, athletic legs and noticeable jaws of spiders (Order Araneae), and the elongated body, coloration, and desert aesthetic of the scorpions (Order Scorpiones), but the 1,000 species or so of solifugid occupy their own lonesome twig on the arthropod family tree. It is generally thought that Solifugae is a part of a larger subdivision of arachnids, called Dromopoda, which also includes scorpions, pseudoscorpions, and harvestmen (daddy longlegs); specifically, combined analyses of the genetic relatedness and shared morphological features of these critters have also linked scorpions, pseudoscorpions, and solifugids together in a grouping dubbed “Novogenuata.” Although, comparative studies on the male genital system have also suggested that solifugids might have a more complex evolutionary history, showing more similarities with mites and ticks in some ways than with their supposed close relatives, the pseudoscorpions. This confusion of what makes a solifugid a solifugid, and its relationship with the rest of the arachnids, would be greatly assisted by fossil evidence, but the fossil record for the Solifugae is pitifully scant, with a few dubious, incomplete, vaguely solifugid-like specimens dating back to about 330 million years ago…and only a few instances of unambiguous solifugids showing up about 300, 115, and 50 million years ago. Most importantly, the earliest stages of this group’s evolution are currently lost to us.

Whatever they are in the grand architecture of the arachnid clan, they are widespread, gravitating towards hot and dry regions of the subtropics and tropics the world over, omitting their presence from only the continents of Antartica and, surprisingly, considering they would fit right the fuck in there…Australia. And wherever they make their residence, they have a very powerful effect on the humans that encounter them, and they have for an incredibly long time. Solifugids, to put it lightly, have an “imposing” appearance and demeanor, with their huge, sharp, pinching jaws, sizable mass, and ungodly overland speed. Consistent first impressions full of everything ranging from a bad case of the all-overs to panicked, wild boot-stomping has undoubtedly earned them immediate recognition as a being assuredly, terrifyingly divergent from other many-legged beasties since antiquity, with the Greeks dubbing the monstrous arachnid “phalangion”, decidedly separate from “arachne”, the spider. More recently, there are accounts of soldiers stationed in North Africa during both World Wars who would pass the time by pitting captive solifugids against each other, or against a scorpion (because why not, I guess), in a fight to the death in possibly the smallest, ugliest, and leggiest gladiatorial showdown of all time.

These brutal spectacles involving dueling “jerrymanders”, another name for the solifugids, were enthusiastically gambled upon, because of course they were. Also, in regards to the aforementioned moniker, if there’s any animal that I could envision being spiritually associated with the deceiptful, ethically impoverished, slimy act of manipulating voting districts, it’s the solifugid…an animal that looks like it would skitter up your leg and chew and burrow its way into your taint if you so much as looked at it sideways.

If you are a solifugid reading this right now (small chance, but you never know), I have to apologize for the upcoming dosage of Truth; y’all ain’t pretty. Spiders and scorpions at least have some measure of gracefulness and an aura of venomous allure…solifugids look like someone tried to cross-breed a centipede with a walrus, and then set it on fire when it came out looking like damnation itself. It is this severe case of “face-made-for-radio” that has allowed these animals to continue to be, to this very day, viscerally upsetting to the point of inspiring mythology and fanciful stories. Although solifugids are routinely found in the American Southwest (where they are called “sun spiders”), many troops (particularly U.S. troops) stationed in the Middle East during the Persian Gulf War of the 1990s and more recently during the Iraq War, encountered these arachnids for the first time…and it wasn’t long before tall tales sent home, and subsequently inflated through the power of the Internet, exaggerated solifugids to preposterous heights. Urban legends in the form of obnoxious chain emails and memes floated around online message boards about these animals cast them as having supernatural capabilities…running fast enough to keep up alongside military vehicles and capable of leaping from the ground and onto the chests of full grown men, screeching and hissing, clacking their drool-slathered pincers (is there any other way?). The name “camel spider” was commonly tied to a claimed habit of disemboweling sleeping camels under the cover of night with the aid of a paralytic venom. The icing on this sci-fi monster cake was the assertion that they would attack and paralyze soldiers, and lay their eggs inside the skin of the unwitting human incubator, ala parasitoid wasps (or Alien…that too), only to have the babies explosively emerge from inside the poor soldier weeks later like a bunch of bloody confetti erupting out of a piñata.

Feeding into this are the highly-circulated photographs sent back to the States, often with the solifugid in forced perspective to appear larger than they are in-person, or conducting some act of eight-legged, predatory horror upon a prey item….conveniently with no real sense of scale.

Of course, just about all of this is hyperbolic nonsense. Solifugids are intimidating, yes, but they pose absolutely no danger to camels or any other large mammal, humans included. This reputation has left the proud, albeit unsightly, Order Solifugae unfairly maligned. I’ve drafted (below) what I think is a more appropriate meme depicting the reality of the unjustly despised, feared, and ostracized solifugid, about which I’m confident the rest of the Internet will give approximately no fucks.

The truth is, solifugids aren’t a hyperaggressive, ancient evil, scouring an exotic, desert landscape in a lustful search for the least leathery leatherneck neck to sink its fangs into…though they certainly look the part. What they really are, however, are an active group of predators that have been fine-tuned by the selective pressures of their harsh environment to produce some incredible, fundamentally badass characteristics. Solifugids have a unique biology that deserves a fair shake at deconstruction and illumination.

Solifugids follow the general arachnid bauplan fairly conservatively, with two well-defined main tagmata (body segments); the prosoma, at the front, containing the “head” and connection points for the eight pairs of legs, and the opisthoma, the meaty, egg-shaped abdomen at the rear. The most obvious, and frightening, distinguishing feature of these animals is their chelicerae…the duel pair of vertically-oriented pruning shears that engulf their face, often reaching sizes larger than the entire prosoma itself. In many other arachnid groups, chelicerae serve as the humble articulating mouthparts, tucked neatly around the mouth hole and mostly out of sight. But in solifugids, the chelicerae are expanded into huge cutting tools, lined with knobby teeth-like projections, resembling a pair of devilish eagle beaks. The entire “head” region of the prosoma, encapsulated by a raised, rounded dome, essentially serves as nothing more than the powerhouse for the chelicerae, and is packed with bulging sets of muscles used to manipulate the double sets of jaws. In fact, the characteristic hump that contains these muscles at the base of the chelicerae is the origin for the “camel spider” name, not any fallacious murder of cigarette company mascots.

If you’re thinking that with all that special muscle devotion and attachment, these chelicerae would be pretty powerful, you’d be right on the money. Solifugids don’t possess the fictional paralytic venom of urban legend to take down prey…the serrated bolt cutters grafted onto their face do just fucking fine. Solifugids are rapacious predators, with incredibly high metabolisms, and a need to track down, capture, and process food quickly. Their ecology, diet, and physiology have led to the evolution of mouth-bound machinery designed to carve and mulch up prey as quickly and efficiently as possible. This is not dissimilar from the likely reason for the evolution of specialized teeth for food processing in mammals; comparatively high metabolisms need to be able to acquire and break down fuel sources immediately and completely. In the same way, solifugids have become eating machines, rapidly devouring anything they can pin down…which is a large number of things. Larger species, sometimes reaching several inches in length, aren’t limited to the numerous insects in their equatorial habitats, and frequently tear into smaller vertebrates with the unrestrained enthusiasm of a sugar-high 6-year old, armed with scissors, on paper snowflake day in arts and crafts. Lizards, mice, baby birds…none are safe from Greedy Gonzales and his Terrible Twins. The chelicerae are more than robust enough to splinter more fragile things…like bones. For this reason, humans that unwisely pester solifugids and end up getting bitten report intense pain and often the drawing of a great deal of blood; most bites from arachnids and insects hurt due to injected proteins from the saliva, but solifugids provide pain with pure force and physical damage.

Humans have nothing to fear, really, from solifugids. But if you’re anything smaller than a baseball? Be afraid. Be very, very afraid.

With rapid back and forth rending of flesh and viscera, the solifugid uses their “cheliceral mill” to pulverize animals as large as itself (not that hard to accomplish when half your goddamn body is jaws), and slurps up the resulting juices and gelatinized remains.

The chelicerae may be excellent tools for bloodily dismembering still living, kicking, and squealing prey, but they also have other important roles to play in the life of the solifugid.

Although solifugids tend to tolerate long periods of extreme heat and aridity better than other arachnid groups, they make life easier on themselves by avoiding some of the harshness of the desert by getting the hell away from the baking solar radiation. They do this primarily by being largely nocturnal, but also by taking cover in the day by seeking out shadows, or digging burrows. Of course, since solifugids haven’t invented shovels (yet), they use the next best thing…their monstrous chelicerae. It probably isn’t surprising that something that has utility in sawing through muscle and bone might also be good for sawing through soil. The solifugids claw at the loose, dry dirt with their mouthparts, only turning away from the laborious activity to clear out their excavation of what they’ve dug out. This is a method used by many burrowing animals, including naked mole rats, which dig their network of burrows using their sharp incisor teeth (and have actually evolved a flaps of skin that keep their mouths from filling with dirt as they work). Observe this industrious little fellow below:

The chelicerae are also used in defensive measures against predators even nastier than they are, and it’s not in the way you think. While, yes, they can and do use their jaws to strike out and give a well-placed nip at an attacker, the chelicerae also have a role in a warning system to would-be fuck-with-ers. This is done through the generation of noise through vibration of physical components of the interior surfaces of the chelicerae against one another. Solifugid chelicerae can be thought of musical instruments of sorts.

This generation of sound from vibrating body parts is known as “stridulation” and it is common in other arthropods, like insects. It’s perhaps familiar to most folks as the origin of the “chirping” of crickets and grasshoppers, which is caused by the running of the surfaces of the wings across one another, and allowing comb-like structures to contact and rub along each other, producing the sound. But stridulation is also found in numerous groups of beetles, as well as arachnids like spiders and our lovely solifugids. All you need are two body parts, known as “stridulatory organs”, to rub against each other to make the noise. This often depends on something scraping rapidly along a finely-ridged surface, generating vibration as it does so. This is the same kind of action that allows fingernails to produce sound when running along a washboard, or for the needle to relay embedded musical recording information as it moves along the tracks on a vinyl record (sound which is then amplified).

The interior surfaces of the solifugid chelicerae are equipped with two major stridulation components; a plate covered in microscopic ridges (a “file”) and a set of stout, forward-facing bristles. The sound is generated when the chelicerae are pressed together and slide past each other, causing the bristles to drag down the file on either chelicerae….and it ends up sounding like this:

While that may sound like the world’s most perturbed Velcro sneaker, scientists believe it has a role in keeping solifugids safely uneaten. Squeaking produced by solifugids in laboratory settings seems to occur in response to perceived threats, and is acoustically similar to the noises made by other arthropods that use warning noises against predators. It has been suggested that solifugids stridulate as a form of bluffing. Solifugids aren’t toxic, and don’t create any venom, but it is highly advantageous to convince predators that they are. One species of solifugid in the genus Galeodes from west-central Asia might use its hissing stridulations as a way of mimicking the noises made by venomous snakes that it shares its habitat with, like the blunt-nosed viper (Macrovipera lebetina) or the Siberian pit viper (Gloydius halys). If you have a bag full of nothing in the face of immediate danger, it might be a worthwhile idea to confuse your enemy into thinking you’re someone who does…and a local, highly-venomous snake is a damn good place to start.

The abilities afforded by the chelicerae don’t stop with stridulation either, because apparently these things are like a damn Leatherman of the arachnid world. Male solifugids have structures on the tops of their chelicerae called “flagella” that look like long, swept-back horns or rigid tentacles. Seeing as how only males possess them, it is thought they have some sort of role to play in solifugid sex, but to be honest, no one really knows what the hell they do. I suppose figuring that out would require researchers to get up close and personal to the gnashing jaws of a sexually ravenous solifugid. I mean, I understand why they haven’t quite unlocked that secret yet because have you SEEN those fucking things?

So, obviously, in solifugids, the head is more or less a battery of powerful tools for survival in the barren desert wastes. Just the chelicerae alone function as steak knives, a backhoe, a furious kazoo, and…maybe something related to sweet, sinful, stomach-churning, solifugid sexual satisfaction? But the legs and body of these critters are equally important and full of exquisite adaptations worth addressing.

Scorpions and solifugids are close relatives, and have both become masters of the desert biome over hundreds of millions of years. However, their strategy for survival here is very different. Scorpions have a suite of adaptations to minimize their output of energy and water. Many species can hunker down under a rock and remain in a type of stasis without eating or drinking for very long periods of time. They move across the desert deliberately, and under the cool of night, and use their venomous sting as a conservative means of procuring food. Paralyze and kill the quarry immediately, so that you can be sure it can’t get away or put up a fight, and subsequently cost you the precious energy. Solifugids took the opposite approach, and live by a mantra of MOVE MOVE MOVE EAT EAT EAT. Solifugids, as I’ve mentioned, have incredibly high metabolisms, and compared to scorpions, ludicrously high growth rates. They live their lives on the fast track, taking the strategy of “getting big quickly and reproducing before the desert has the chance to kill you.” Solifugids are all about running around and killing soft, vulnerable things, and outside of their gigantic chelicerae, they have key adaptations for sprinting around at blinding speeds, maximizing each kill’s energy yield, and making damned sure every meal and mating attempt goes according to plan.

Understanding how solifugids navigate through their world is key to understanding how they manage to survive and consume so much in a place with so little resources to offer. Solifugids only use three of their four pairs of legs for locomotion. The first pair of legs, up near the head, are thinner and more delicate, and are usually held just off the ground and act like antennae, rapidly trailing and sensing the environment via touch as the solifugid motors along. In front of these legs are a pair of pedipalps, appendages that look like legs, but are not, and are more often associated with the mouthparts in arachnids (the pedipalps of scorpions, for example, have been modified into the pinching claws). In solifugids, they are huge and elongated, and often look so much like legs that people regularly report sightings of solifugids as “big, ten-legged spiders.” These pedipalps are also instrumental in sensing the path directly in front of the solifugid. With three pairs of appendages powerfully propelling the animal forward, and two pairs elevated in the air, the solifugid is like some kind of arachnid centaur.

Solifugids move about in this way insanely quickly, flying over the hot sands at 10 mph (16 kph)…which is quite a feat for an animal smaller than an iPhone. While there are other invertebrates that, for their size, are faster than solifugids (for example, the pint-sized tiger beetles come to mind), nothing without bones really comes close to these speeds, which are close to what an adult human can accomplish at a sprint. So how do they manage to do this?

The answer may come from how they fuel their bodies with oxygen. Solifugids, along with the Opiliones (harvestman/daddy longlegs) and the pseudoscorpions, don’t have book lungs, which are the typical respiratory tissues found in arachnids. Instead, like harvestmen and pseudoscorpions, they have a network of small tubes running in and out of their bodies that allow the exchange of oxygen and carbon dioxide to occur. This system of tubes (“trachea”) are very highly developed in solifugids, much more so than in other invertebrates with tracheal systems. Solifugids also have multiple pairs of spiracles (holes) that pump large volumes of air in and out of this network with great efficiency. These bastards are able to visit blistering, swift death upon everything that creeps and crawls under the desert sun because when evolution was passing out engines, they got the 8.0 liter, quad turbocharger, 64-valve, 1,300 horsepower version. Solifugids aren’t so much animals as they are wire cutters super-glued to a rocket.

This constant incredible athleticism means that the solifugid must carbohydrate load 24/7, and make sure that if it runs down lunch, it better come out on top. Part of this is facilitated by the vice-like grip of its chelicerae, but that requires getting close enough to chomp down. This is where the pedipalps come in, which have eversible suction pads on the tips. These little structures stick right on the prey in mid-chase, allowing the solifugid to get a grip and pull the hapless victim straight into the torturous embrace of its esurient maw.

To get an idea of what this would be like, imagine you are a lone agama lizard, taking a night stroll on the flanks of sand dune in the middle of Sahara in search of a wayward beetle or two to snack on. Then, you hear something clambering over the ridge of the sand dune…and it’s approaching fast. Really fast. Before you can even react, a hideous vessel, festooned in flailing jaws and legs, clears the top of the dune, and races down after you. You can’t get your footing on the loose sand in time, but the solifugid, dancing on the shifting surface with its light, hairy feet, has no problem at all. You turn to flee, and just as you do, terror grips you as you see those fucking toilet plungers of death eagerly reaching out towards you. You skitter down the dune, sand flying, your little lizard heart pounding. The solifugid, aided by gravity, gets closer, bearing down on you, a vast tank driving a flurry of clacking car compactor claws, slicked with saliva, horrifically screeching as they rub past one another. Suddenly, you feel one of the suction cups adhere to your scaly side with a sickening wet pop, and you are yanked backwards. The sound of the rustling pincers to your back ceases right before they come down on your belly with tremendous pressure. You let out a pitiful yelp as the solifugid silently, coldly, articulates a massive jaw over your head. It easily collapses your skull, and everything goes black.

That’s the day to day reality for anything small sharing the desert with these animals.

Those nifty little suction pads? Yeah, those are perfectly suited for grabbing flying insects out of the goddamned air. Solifugids will take and eat anything they damn well please. Flying away only prevents the inevitable in the desert.

Solifugids are apparently so voracious, that they are known for eating themselves into a bloated stupor, so swollen with food they can’t even move. Their soft, stretchable abdomens expand with liquefied food like a water balloon attached to a sink faucet. This allows them to obtain as much food energy as possible in a very short amount of time, a skill I learned and exploited whilst around free food in my college years.

In addition to those weird flagella on male chelicerae, there are other organs adorning the Solifugae that are a complete mystery to science. I’m specifically talking about a set of organs on the underside of the last pair of legs that jut out from the exoskeleton and are shaped like ghostly white ginkgo leaves, or mushrooms.

They are called “malleoli” and while scientists are pretty sure they are sensory organs, they don’t really have any idea what they are sensing, or how they are doing it. The odd, fan-shaped structures might be sensitive to vibrations traveling through the ground, or to chemicals in the air, but science, as of right now, has given the colorless, gummy umbrellas a collective shrug.

If a solifugid manages to violently consume its way out of childhood and grow to full, reproductive age, it may be struck by the urge to settle down and have a clutch of baby camel spiders all of its own. But reproduction is easier said than done in the world of the solifugid. These are purely solitary hunters, and because of this, mating opportunities don’t exactly spring up naturally like they do in socially-competent humans (er, well, most humans).

If you were a solifugid, being a loner for much of your life would actually be a very wise idea. You see, it turns out that an animal that instinctively looks at anything in its own size range as a meal doesn’t tend to play nice with other solifugids. These creatures are not big on long term relationships…or short term relationships…or the equivalent of a coffee date…….or anything. What they (and by they, I mean the female solifugids) are a fan of is ripping apart and devouring anything that tries to mate with it. That unstoppable appetite is indiscriminate, and well-meaning gentleman callers don’t get a free pass. Solifugid mating protocol is made exceedingly complicated by the ever-present threat of sexual cannibalism…which in reality is nowhere near as hot as it sounds, pervert.

From the perspective of a male solifugid, female solifugids are gargantuan monsters twice their size, insane with insatiable hunger, and able to cleave them in two in a fraction of a second. But…they also want to have sex with that gargantuan monster, beautiful creature that she is. In order to get around this seemingly insurmountable dilemma, in many species of solifugid, the males have acquired a number of special adaptations, both physical and behavioral, that allow them to sow their seed and make it out alive.

A conventional approach, used by many species of solifugid, is for the male to excrete a spermatophore (a dense sperm packet), which is then placed on the ground near the female. The male then “courts” the female by some very cautious massaging and dancing around. This is less “taking the lady out for a nice meal” and more “dangling a steak in front a tiger’s face.” Once the hungry hungry horror is lured into the perfect position, the male takes a deep breath through his tracheal spiracles, and does the unthinkable. He grapples the female, holding onto her back tightly with the suction pads on his pedipalps, and supplexes her onto the spermatophore, which he then plasters into her genital opening. This is like if you needed to stick a wad of gum on the belly of a grizzly bear, and you tried to do so by tackling it from behind and attempting to pull it to the ground, equipped with nothing but a couple of suction tip Nerf gun darts to increase your grip. After the objective is complete, he lets his immeasurably pissed “partner” go and books it in the opposite direction as fast as his post-coital legs can carry him.

Males in some other species, especially ones with a high degree of sexual cannibalism, have to struggle even more to pass on their genetic material. Observations of mating behavior in species of Galeodes and Gluvia, in which sexual cannibalism runs rampant, have illuminated a complicated and life-threatening bit of “coercive” copulation that males must endure. And by “coercive” I mean “forced.” In order to subdue the female long enough to slap some baby batter in her genital opening, the male employs a bit more than just a fancy wrestling move. He approaches carefully, with or without some strokes from his pedipalp, and then lunges, chomps down on her legs and abdomen, chews at her genitals, hooks and locks her hind legs with his own, and after she’s pinned, he transfers the spermatophore. There is no cuddling afterwards.

When solifugid children ask their parents where babies come from, the response they receive is a flat, solemn “Pain, child. Pain. All of life is pain.” And then the parents decapitate the young and feed upon its kidneys, because, you know…solifugids.

These encounters can get so heated that males can inflict substantial injuries upon the female, including puncture wounds, scrapes, and occasionally the severing of an entire limb. These kinds of “love amputations” are apparently just a ho hum part of the savage life of the solifugid.

Mating is so treacherous for male solifugids that they’ve actually evolved a series of physical adaptations to make their screw-jitsu moves that much more successful. For one, males in these sexually vicious species tend to have proportionally longer legs and small bodies, allowing for greater agility and an increased reach, which helps in keeping Princess’s unholy gob of horrors as far away as possible. Males also have stronger, stouter, pokier spines along their pedipalps, which are likely used to hold on to Miss Buckin’ Bronco until the deed is done.
Yes, solifugid sex is so violent that only males that have a natural, morphological edge (like built-in crampons, for fuck’s sake) in going head to head with the most fearsome thing in their world (a hungry, full-grown female solifugid) are able to send their genes into the next generation.

Solifugids are undoubtedly ferocious predators. They kill and eat almost everything they meet up with. Insects. Spiders. Lizards. Snakes. Baby mice. Bats. Birds. Friends. Family. If it can be caught, they’re on it, gobbling up as much as they can in their short lives (estimated at only about a year or two maximum). They are the baddest motherfuckers to scan the seas of sand, but unlike what the urban legends purport, their sphere of terror is limited to the realm of the diminutive.
Despite the impressive role they play as tenacious predators in their ecosystem, we don’t really know much about them compared to other arachnid groups. Hopefully, in years’ time, more people will know of solifugids for their very real, very fascinating biology, and not relegate the order to the isolation of limited inquiry, superstition, and misunderstanding.

Image credits: Intro image, scorpion vs solifugid illustration, original for Forever Alone solifugid, chelicera close-up, solifugid threat display, pale solifugid with large prosoma, malleoli, solifugid on road, ending solifugid

© Jacob Buehler and “Shit You Didn’t Know About Biology”, 2012-2014. 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.