- Level 1-3 Flyer Attack
- Level 1-3 Flyer Carapace
The Spire also allows the research of two upgrades: Flyer Carapace for air unit armor and Flyer Attack for air unit attack. Only one level of each upgrade can be researched at the Lair stage. Once the Hatchery morphs into the Hive, the Spire can be upgraded to a Greater Spire, which allow both further Flyer Carapace and Attack upgrades and two advanced Zerg air units, Guardians and Devourers.
The Spire is an extremely important tech option for Zerg in all three match-ups. The Zerg player may elect to build the Spire in a furtive location hidden from plain sight to gain the advantage of surprise against the opponent.
- In the ZvZ match-up, most games revolve around a race to build the Spire as quickly as possible while not losing to the opponent's Zerglings.
- In the ZvT match-up, Mutalisks are very useful for harassment and stalling while the Zerg advances to Hive technology. The Spire also permits Scourge, which are are essential for destroying Science Vessels.
- In the ZvP match-up, Mutalisks can be used for probe harass or for sniping High Templars, and Scourge are very useful for sniping Observers, which prevents the Protoss from being able to detect Lurkers. Scourge are also very useful against Corsairs and Shuttles. A Spire is a worthwhile addition, even if it is only used to counter enemy drops with Scourge, without getting Mutalisks.
The Spire has a high cost, a long build time, and fairly low health, so it is fairly vulnerable and a good target to be sniped in drop play by the opponent.