Nephila

 S 

''Nephilae are large spiders found in the deepest caverns, where they spin webs of the purest gold. They are relatively non-aggressive, and their chitin comes in a wide variety of hues.''

Nephilae are giant subterranean spiders that live in the third cavern layer. Unlike Vanilla DF's Giant Cave Spiders, these beasts are not fatally poisonous; the worst you'd get from a Nephila bite is some pain and blistering (ignoring the fact that a spider more than twice your size just bit your arm). They do spin webs, however - and not just any ordinary silk web.

The web of the Nephilae are solid gold.

Nephilae golden silk is amazingly valuable, seeing as how it comes from mythical beings near the earth's core, and should be all the incentive required to go hunting for them. The spiders themselves are uncommon, making capturing a few a challenge, but for the avaricious, economy-minded halfling, they are worth it.