Loitering shamelessly on the Internet and ignoring my role as Protector of DarkSyde Manor, I was startled the other evening by a blood curdling, feminine shriek of horror coming from the garage. "HOnnnneeeeeyyy!!!! heeeelpp!". Running to the aid my Damsel in Distress, I whip open the door to find her backed up against the wall next to the washer and dryer, her face contorted in abject terror, and a shaky finger pointing at ... a snake? An alligator? An armed intruder? Nope; a tiny arthropod, taxon Aranaea, between my wife and
safety. The itty-bitty female spider had set down beside her, bravely displaying the upper two legs in warning; It was enough to have Mrs. DS 'pinned'.
Below: Large and Creepy Graphics Warning!
Despite my admiration, both scientific and from a climber's perspective, for spiders, I'm sad to say Mrs. DarkSyde will never appreciate the beauty of the order
Araneae. She in fact took some offense when I tried to explain her recent interspecies 'face off' from the spider's viewpoint! But you my fellow science geeks will surely enjoy a review of the evolution and physiology of these amazing critters, which have crept and crawled on our planet since before our ancestors had a spine!
They're the stuff of nightmares, science fiction shows, Icons of horror, and rightfully so: Predators each and everyone, with a bite that can kill, maim, or debilitate a human for life. These critters are creepy! They're natural born climbers, they live life on the edge, literally hanging on by a thread. Like a B.A.S.E Jumper, they'll leap off a building without flinching. They climb sheer walls and spend the day upside-down. They're hairy thrillseekers with a taste for blood, more legs than you, and there are probably hundreds of them living in your home!
But they're also amazing animals and represent the first known metazoic pioneers to crawl on land. They live by their wits and their skills in jungles and deserts, from treetop canopies to subterranean tunnels, and even underwater. Spiders are masters of both biome and biochemistry; they can sail to thousands of feet in altitude and travel for hundreds of miles on windborn silken parafoils, cling to the side of a granite face hundreds of feet off the ground in gale force winds, and walk across water; they lure insects by imitating their mating pheromones, spin webs of silk stronger than steel and five times as elastic, and liquefy their victims internal structures with acidic poisons and peptides.
Spiders belong in the phyla Arthropoda along with over one-million other species such as crustaceans and insects, making it the most successful phylum on our planet by far. Arthropods make a dramatic appearance in the fossil record in the Cambrian Period over 500 million-years ago. One so dramatic it has been termed The Cambrian Explosion and one so poorly understood it has been seized by Creationists as evidence of ... well, something; they're just not sure what.
The class of Arachnida, Latin for spider, contains not just spiders themselves but mites, ticks, scorpions, and our childhood friends, Grand-daddy-long-legs. But spiders are by far the most numerous of the arachnida, with almost 40,000 known species making up the Order of Spiders known as Aranaea.
Spiders have no internal skeleton or external shells with thick, hard parts, and thus aren't likely to fossilize well. Lacking a central cardiovascular system, they're dependent on book lungs, tubes running through their bodies, to distribute oxygen and collect waste using osmosis. Because of this, and the square/cube law, there will never be such a thing as the classic giant spider of cheesy movies-or at least if one is somehow engineered it's hard to imagine a creature that would be more helpless and short lived. They would literally be unable to move, probably spread into goo, and suffocate, all at once.
In our Spider evolution timeline, we have only a few fossils from the 230 to 65 million years ago, and even less from the Paleozoic Era (Cambrian, Silurian, Devonian, about 600 to 240 MYA). Needless to say a delicate structure like a web is going to be wholly absent, silk lined egg sacs, spinnerets, and burrows however do preserve giving us some insight into the development of silk production among arachnids.
The reason the fossil record reveals much more about spiders during the reign of the dinosaurs is due to the growing success of resinous trees which allowed for insects and spiders to be trapped in amber; a process made famous courtesy of the movie Jurassic Park. We have about 200 or more species of spiders from this time. Two-hundred isn't much considering the thousands of species that must have lived then, but this is the best record we have. Following the K-T extinction, the number of spider fossils dwindle and doesn't notably improve until the last few million years.
One the most familiar representatives in the early fossil record, which may be a direct or closely related, indirect ancestors to modern spiders is the lovable trilobite. Other close relatives of the spider were truly horrific, such as this monster euypterid or sea scorpion from 450 MYA, which measured a nightmarish two meters in length!
One of the earliest known spiders, not quite a modern version but close indeed, is this alien looking sea spider from 420 million years ago, below. Some researchers feel this lady belongs in the same taxon as modern spiders, others disagree.
A number of Carboniferous arachnids called Trigonotariabrids resembled modern spiders (Some of which are roughly a meter long). They appear in the record at about 400 million years ago. Trigonotariabrids deserve a special mention as they are among the first animals to walk on land, respired through book lungs, spun silk, and walked on eight legs. However, they were probably not directly ancestral to spiders, more likely representing an offshoots of extant Arachnida.
The first clear 'true' spiders crop up around 380 million years ago in the Devonian Period also known as the age of the fish. Early Attercopus fimbriungus and her ilk are mesothelids meaning they had silk producing spinnerets located near on the underside of the abdomen near the mid section as opposed to the rear as spiders do today. Although at least one hardy mesothelid, the Malaysian Trapdoor spider did make it into modern times
So-called modern spiders are placed in the sub-order Opisthothelae, have spinnerets at the end of their abdomen, and rarely show clear segmentation of the abdomen. Opistholelae are further subdivided into big, hairy, tarantula-like denizens, which includes trapdoor and funnel webs spiders called Mygalomorphae, and the vast majority of other spiders called Araneomorphae.
Electron scanning micrograph of spinnerets ejecting new silk
All spiders produce a biomolecular protein polymer called silk, although not all spiders produce all the different types of silk known in the spider community. Spider silk is an amazing substance which emerges as a liquid from the spinnerets, each composed of hundreds to thousands of microscopic tubules, and solidifies into a springy line on contact with the air; although to this day materials scientist are not clear on the chemistry. This is understandable as the process of setting up is virtually instantaneous and almost impossible to observe. A pity we can't emulate it; the silk converts from an atomic weight of 10,000 or so to an atomic weight of 200,000 or more, thus making silk an extraordinarily complex substance. Depending on how you measure it, it is stronger than steel, lighter than nylon, and more elastic than rubber!
Spider silk would make an excellent material to use for all kinds of applications. But harvesting it on a commercial basis will have to wait until we can synthesize it cheaply. Spiders remain uncooperative in providing it for us in farms: Put a bunch of silk worms in a box and they'll happily stay put and spin silk: Put a bunch of spiders in a box and in no time you'll have a box full of dead, half-eaten spiders!
The uses they have put that ability to vary enormously in the order Araneae. Silk serves as draglines, transportation vehicles, webs of every shape and size. Orb Weavers are the architects of the stupendous 'wheel' webs we see lined with dew in the light of dawn, trap door spiders monitor a tripwire network from beneath their swinging doors disguised with leaves and soil, one spider even whips around a bolus while suspended from a single thread, wielding it like a sticky lasso to snare passing prey.
But one utility for silk production they do seem to all have in common is the silk lined egg pouch. Now would be a good place to insert a quick review of Spider Sex. But in today's blogosphere, when the topic of Spider Anime or invertebrate sex gets passed around like a cephalopod sperm packet, there really is only one man who rises to meet the call. PZ Myers doesn't let us down with the short, but well illustrated, missive of Spider Kama Sutra.
But of course what makes spiders dangerous is the business end: Fangs and poison. Spiders are carnivores who inject their prey with a toxic cocktail loaded down with homemade proteins, amines and polypeptides, which first immobilizes their victims and then turn their innards to slush to be sucked up at spider's leisure.
One of the most deadly of such creatures is Australian Funnel Web Spiders. The Funnel Web possesses hardened fangs that can bite through a fingernail several times in one or two seconds, each bite injecting an atraxotoxin which causes major breakdowns in the transmission of nerve impulses.
Various species of Black Widow are found in Australia (The Redback), Europe, and North America, where she prefers to dwell in dark, sheltered places. Although her bite is dangerous, Widows are not generally aggressive and prefer to live quiet lives consuming enormous numbers of insects snared in their tangled webs. The Black Widows get a bad rap in name alone; she does occasionally eat her mate after sex, but not as a rule, unlike a number of other spider temptresses who are far more likely to consume their hapless consorts (Yes my fellow y-chromies, spiders fought the battle of the sexes long ago and with a few notable exception, we males utterly lost. Manly spiders are mostly relegated in spiderdom to the role of sperm provider and occasional post coital snack).
And of course the Brown Recluse is fairly well known as a spider which leaves a spot of dead tissue after delivering one of it's painless, 'stealth bites'. This area of necrotic tissue, resembling a chemical burn, is rarely life threatening ... with the caveat that any substances are of course deadly if you're allergic to them. But the Brown Recluse packs a macabre fate for an unlucky few: In a few cases of recluse envenomation, a disfiguring and sometimes fatal autoimmune reaction and recurrent infection is set up in the victim which may last a lifetime: Necrotizing Fasciitis.
But enough with the few bad actors in the spider community, let's look at some of the cool ones who wouldn't hurt a ... well, they'd probably be happy hurt a fly: but they probably won't hurt you, nor do they want to.
A wolf spider like the one that had Mrs. DarkSyde pinned down. These ladies look much worse than they are.
A male and female Red-back Jumping spider briefly size each other up as mating partners.
A rare jeweled Spiny Back Orb Weaver
The Water Spider, the only underwater spider known. This animal keeps a store of oxygen in a bubble held onto its abodomen when she's out and about, and a larger reserve in it's underwater web which is built like a diving bell
Crab Spider with a brood of young emerging form the safety of their artificial silken womb
A jumping spider sizes up a leap. Jumpers sport quite an impressive visual array consisting of four to eight full blown camera eyes, providing these spiders some of the highest resolution, stereoscopic, color vision out of the entire group of invertebrates
As long as there is prey there will be predators. And chief among the smallest hunters will be the spider. Spiders employ a long term strategy which has seen them through every catastrophe known to earth science. They are battle tested and hardened veterans of the terrestrial environment; they've been scuttling around as long or longer than any other type of animal on earth. Odds are spiders will creep and crawl over our world long after we humans, or even vertebrates for that matter, have changed beyond recognition, or disappeared from the cosmic drama altogether.
Yes, they're startling to come across unexpectedly. No one says you have to be friends with them and most of them aren't endangered so if you have to smash one, do it. But bear in mind, these magnificent arthropods also keep down the insect populations including those bugs which can truly do mankind widespread harm: Mosquitos, fleas, cockroaches, and flies, just to name a few. Most spiders can't hurt you, they will never turn into the megagiants of sci-fi horror shows, and they're perfectly willing to leave you alone if you leave them alone. Far from the terrifying, archetypical creatures of film and nightmare, they're astonishingly successful insectivores, superb architects, acrobats beyond compare, and engineers extordinaire. Mrs. DS may not care to appreciate their brand of beauty and elegance, and I don't ever expect her to change. But we can.
