Are these truely a "coastal" species? I suppose they must live a long time, and could very well migrate. -- Desert viking
They would have to be very conservative in how they expended energy; moving slowly, reproduction cycle would take decades, etc.19:39, January 17, 2012 (UTC)ehudwill
Moving slowly and reproducing rarely certainly helps conserve energy, but they'll still have a base metabolic rate that would require a very significant amount of food. For instance, the blue whale is the largest known animal to have ever existed, and it's only 100 feet long and 200 tons. They eat 7000 pounds of krill per day. Granted, a fair amount of that is probably expended moving their massive bodies, but even assuming 1/4 is expended purely to keep breathing and blood circulating, we're looking at almost 2000 pounds of food per day. For a creature with a body length around a mile (based on a leg-span of 2 miles, 1 mile seems reasonable, depending on how the square-cube problem is solved), we're looking at tens or hundreds of thousands of pounds of food per day simply for basic metabolic function, and whenever it did move, it would require thousands of pounds of food just to walk the length of its own body.
And that's the easy problem. The harder problem is the aformentioned square-cube law, that is, "If an animal were scaled up by a considerable amount, its relative muscular strength would be severely reduced, since the cross section of its muscles would increase by the square of the scaling factor while its mass would increase by the cube of the scaling factor."
The largest known terristerial animal is a sauropod, which was only 38 feet tall, 82 feet long, and 65 tons and was built like a really big elephant where leg structure is concerned. For a creature with the leg structure of a spider (legs jutting from the side of the body), those legs would have to be impossibly strong, the body would have to be impossibly light, or, more probably, both, in order to support its weight in ways that even modern engineering hasn't solved for artificial structures.
Or, put more succinctly by J. B. S. Haldane, large animals do not look like small animals: an elephant cannot be mistaken for a mouse scaled up in size. The bones of an elephant are necessarily proportionately much larger than the bones of a mouse, because they must carry proportionately higher weight.
Azuaron 20:27, January 17, 2012 (UTC)
I originally created them because they sounded cool; now I'll have to figure out how they might actually work... :D
OK: As far as food goes, they (at least the older ones) could have a symbiotic relationship with a species of algae or other photosynthetic organism, which would lessen (maybe almost entirely remove, depending on just how slow the spiders move) the necessary energy intake. Eating food for giant spiders would then be as eating vitamins (and protein...) is for humans. This would give the humans one more potential food-source, and make the spiders dependant on acquiring the algae (probably from the sea) for growing past a certain size.
And for strength, can I postulate Adminium?
Symbiotic moss might be the way to go. The moss' root system could be intertwined with the spider's circulatory system and enable the transfer of nutrients between organisms. The moss would also function as a distributed pulmonary system, dropping oxygen directly into the spider's blood, which solves a part of the square-cube problem (an animal that big would never be able to breathe with conventional lungs). This also tells us the best (and, possibly, only) way for humans to kill such a beast: scrape off the moss and it will suffocate.
As for material, it's always preferable to stay away from handwavium as much as possible, both because it tends to cause problems in other areas (armor made from handwavium! If there's enough for mile-long spiders, there's enough for anything), so I'd recommend a titanium alloy. Titanium, in addition to be incredibly strong with a well defined hexagonal crystal structure, is the ninth most abundant element in Earth's crust and wasn't forgeable until the 1900s. Plants are already good at extracting titanium, so that can be something else the moss does. Which means we may have solved the eating problem: giant spiders eat dirt and sea water, which their moss then turns into useful materials.
Titanium alloyed with what? Don't say. Most readers won't notice, and the ones that do will make up a better answer than we can think up.
The spiders would instantly become valuable commodities for their titanium-laced shells: lighter and stronger than steel, even if they couldn't get a fire hot enough to forge it.
Finally, we have to toy with the idea of an abdomen that's largely hydrogen-filled (or some other light gas, or a vacuum). Buoyancy is really the only way to make this thing not collapse under its own weight, particularly with legs jutting from the sides, but, of course, there's a reason why there's never been a mile-wide airship. It's a better explanation, but still not one that would really work. Further, if the top of the abdomen is just a shell filled with hydrogen, the moss wouldn't grow there, and that could provide space for the human village you want to stick on it without endangering the life of the spider by the humans scraping off moss. And provide a way for invaders to take out the humans (burst the shell and ignite the hydrogen).
Azuaron 14:22, January 19, 2012 (UTC)
Why not move the whole thing into the water. The abdomen would seem like a 'living island' while the legs stretched underneath under the surface of the water. The moss would then convert the H2O to Hydrogen for the abdomen and oxygen for the spider itself. The Hydrogen would then not have to be in excessive amounts to create boyancy for the abdomen. Obviously the spider would be limited to very slow and lathargic movement - maybe once a season to move with the change in heat/food source. This would also create a great ecology on the square mile of terrain of the 'floating Island' - for instance, the abdomen would have to secrete excess Hydrogen into the atmosphere - so how would that effect the Flora and Fauna on it's 'back'. Just a thought.
Jim 23:33, January 19, 2012 (UTC)