Gossamer

Description
Harvested from the webs of spiders, gossamer can be spun into a durable, strong thread. Gathering gossamer would require weeks were it not for the presence of extremely large spiders in the Exiled Lands. Their webs are large enough that gossamer gathering can be a profitable enterprise. It is not known what causes the spider in the region to grow to such an extreme size, but enterprising Stygians have been harvesting gossamer here for centuries.

Source
Gossamer can be acquired from spider eggs, with a bonus when using a sickle.

It can also be harvested from the following creatures while using a sickle:

Media
Spinnfäden