See the video here:

http://www.youtube.com/hdstarcraft#p/u/0/HiFiQ6nI70A

Basically you cancel the drones right before they come out, and you get both the minerals and larvae back. Makes the 6-pool rush downright ridiculous.

Zerg players have fun while you can. This is getting hotfixed fast (I hope - Blizz are you listening?).

This is a known issue, a post confirming this and the fix-in-progress can be found here: I havent seen any Blue respond to Larva issue http://forums.battle.net/thread.html?topicId=24401524314&pageNo=1&sid=5000#11

Please try to stay on topic so that a thread that is potentially useful to players doesn't get locked due to banter.

Thank you!