§ Of the Sindar The Silmarillion

And ere long the evil creatures came even to Beleriand, over passes in the mountains, or up from the south through the dark forests. Wolves there were, or creatures that walked in wolf-shapes, and other fell beings of shadow; and among them were the Orcs, who afterwards wrought ruin in Beleriand: but they were yet few and wary, and did but smell out the ways of the land, awaiting the return of their lord. Whence they came, or what they were, the Elves knew not then, thinking them perhaps to be Avari who had become evil and savage in the wild; in which they guessed all too near, it is said.