I was farming this in the great divide for my baby Necromancer's pet spell. I was looking for the young shardwurms and found only an elder shardwurm. Thinking it could be a placeholder, I killed it. And the words of allure dropped off the elder shardwurm.
It doesn't seem to be a very common drop, though. I killed every wurm in the caves along the middle of the zone, even the broodmother, who resists every spell I threw at her, including my chromatic nukes, and none of them dropped these words.
Just to let you know, the elder shardwurms can drop them, too.