From Zelda Legends Wiki
Skulltula is a spider that likes lurking in dark places and on the roof. When a victim comes near, the Skulltula will fall down and scare people, and often it tries to hit the victims, too.
The Skulltulas can be identified by the Skull-mark on it's back. The Skulltulas are big-sized, and they like to travel and hunt alone, not in packs like Keeses.