I'm not sure but if you choose in SC2: HotS campaign your **zerglings** evolution into **[swarmlings][1]** (3 from one larva) you can have biggest army ever.

If this one zergling take 0,33 supply you should have maximum number of (**OMG!**) **600 zerglings** on map!


  [1]: http://starcraft.wikia.com/wiki/Swarmling