according to the lord of the rings, ents proclaim to be the most ancient of all creatures on middle earth. yet neither the ainulindale not the rest of the silmarillion explains their creation. there is a passing reference to the trees by yavanna in 'of aule and yavanna' as creatures who sang to Illuvatar amid the rain and wind...the word ents not being used explicitly anywhere.
when do the ents come into being then? they are neither valar nor the first nor second born. are they mentioned in any book outside of LOTR, hobbit and silmarillion or was this a lapse in continuity on tolkien's part?
it is explained all right, the ents are spirits sent by Eru on Yavanna's bidding to protect the trees from Aule's dwarves' axes. it is somewhere in the silmarillion : soon after Aule has created the dwarves and Eru decides to keep them alive, Yavanna begins to worry against Eru that the dwarves will destroy the trees or something. check it.