From WoWWiki

Shadowthread Cave is in the northwest corner of the Shadowglen in Teldrassil. While it has always been home to the great spiders of Teldrassil, recently the spiders have become increasingly hostile and the cave much more dangerous. The largest spider in the Shadowthread Cave is named Githyiss the Vile, a particularly nasty specimen that has been the bane of more than one inexperienced Kaldorei.

Subzones of Teldrassil
Aldrassil • Ban'ethil Barrow Den • Ban'ethil Hollow • The Cleft • Darnassus • Dolanaar • Fel Rock • Gnarlpine Hold • Lake Al'Ameth • The Oracle Glade • Pools of Arlithrien • Rut'theran Village • Shadowglen • Shadowthread Cave • Starbreeze Village • The Veiled Sea • Wellspring Lake • Wellspring River