A little detail (I don't know if it was this way already).
http://img252.imageshack.us/i/img0465a.jpg/
Translated:
Spawn Larva
Target Hatchery, Lair or Hive spawns 4 larvas in 40 seconds.
If target Hatchery, Lair or Hive has more than 3 larvas, regular larvas production is halted till it has less than 3.
So I hope it's easy to distinguish Queen Spawned larvas from regular ones...on the contrary you will be forced to evolve ALL larvas before using Spawn Larva again on the same Hatchery.
This is not an issue, I Think, if you have only one Queen at the target Hatchery but...if you have more than one?