You never feel sadder for a spider than when you’re watching one of those nature films where a wasp paralyzes a tarantula and then lays eggs in it—eggs destined to hatch into grubs that devour the spider alive. The spider eater is that wasp for giant spiders…and for humanoids if the pickings are slim, courtesy of its paralyzing poison. Worse yet, the spider eater is a dimly intelligent magical beast, not vermin. Careless PCs should beware…
An alchemist seeks spider eater organs as stock for freedom of movement ointments. Finding a brood of them means going into the chaparral, where they must face not only spider eaters but also giant spiders, great desert owls (treat as giant eagles), and magical cacti whose sleep venom spines are as much a threat as the spider eaters’ stings.
Araneas hate spider eaters, for obvious reasons. An aranea wizard hires adventurers to wipe out spider eaters near his tower. However, the paranoid aranea assumes that anyone injured or paralyzed by the spider is a potential host. If anyone in the party returns wounded the spider-mage wastes no time with healing or clerical magic—it attacks them immediately to ensure no new spider eaters are hatched.
Serfs who flee the devil-worshipping land of Corrus often seek refuge in the Orbwood, preferring the threat of spider fangs to the lash. The border town of Hornet Glade has come to an unusual accommodation, living openly with spider eater allies who nest in abandoned barns on the edge of town. The spider eaters keep Hornet Glade safe from arachnid incursions, but the price they charge—a dozen victims a month, usually new refugees or tradesfolk—will seem too high to most adventuring visitors.
—Pathfinder Bestiary 3 255