These Spiders, in their adult form, take the word Giant to a whole new meaning! They can grow until they span up to two miles from foot-tip to foot-tip, and their bodies are large enough that an unusual nomadic people often resides in houses built on their backs.
The older Giant Spiders have a symbiotic relationship with a species of photosynthetic moss. The moss' root system are intertwined with the spider's circulatory system and enable the transfer of nutrients between organisms. The moss also functions as a distributed pulmonary system, dropping oxygen directly into the spider's blood. The older Giant Spiders are extremely dependant on this moss: if more than 25% of it is scraped off, the Spider will rapidly die.
Once a Giant Spider ages and slows enough to begin growing significant amounts of moss, it begins to regularly ingest significant amounts of earth and seawater. At first this supplements the Spiders' regular diet, but it eventually replaces living creatures (except for occasional trees) altogether. The earth and seawater supply the moss with several essential nutrients, some of which are given back to the Giant Spider. Most notably, the moss slowly collects titanium and several other metals, and the Giant Spider uses these to replace its ordinary exoskeleton. Full-grown Giant Spiders have nearly indestructible titanium alloy exoskeletons.
Their young are a mere two feet tall, and are the Vitures' chief predator.