If multiple hatcheries are selected, pressing the "S" hotkey will select all of the available larvae at all the selected hatcheries. The player must press a hotkey (or select a morph icon) once for each unit they wish to build.
Queens can target a hatchery/lair/hive, causing it to eventually spawn four larvae. These join any already-present larvae. The larva-producing structure will not naturally produce any more larvae until the total falls below three. The larva count for any given hatchery/lair/hive cannot exceed nineteen, no matter how many times spawn larva is cast.
The ability to spawn additional larvae can indirectly help the zerg economy, as this enables them to produce a high number of drones (or a high number of combat units, or a mix of both).[3]
Centurion Queen
