ON THIS WIKI
The Flamestring is an item added by the Natura mod. It is dropped by Heatscar Spiders, which spawn in the Nether. The string can be used to create different special bows added by Natura, which require Bloodwood, Darkwood, Fusewood or Ghostwood to be crafted. Also, if you have Tinkerer's Construct installed, flamestring can be used to create a Fiery Bowstring, which is used when crafting a shortbow in order to give a flame effect to arrows being shot.