Sting (Middle-earth)
Sting has the magical ability to detect orcs or goblins nearby, glowing blue in their presence, as it did when the Fellowship encountered orcs in the mines of Moria. Tolkien establishes this as a common property of First Age Elf blades, particularly those forged in Gondolin. Sting is also exceptionally sharp. Bilbo manages to thrust it without effort deep into a wooden beam at Rivendell. Frodo also wounds a troll in Moria, after Boromir notches his own sword with his attempt. Sam uses Sting to cut through the giant spider Shelob's strong webs with ease, and also wound the spider, driving it away from the paralyzed Frodo.
Gondolin
The dagger Sting was known to have special powers against giant spiders (distant offspring of Ungoliant) and could cut their webs with ease. It also was highly effective against Shelob, cutting the spider's eyes and wounding her sufficiently that she fled in pain. Whether the longer Gondolin swords mentioned in Tolkien's works had similar powers versus spiders is unknown. Such creatures were common in the Ered Gorgoroth south of Gondolin.