The Drone is the Zerg Worker. It can gather Minerals and Vespene Gas, it has a low-damage ranged attack (range of one), and it can morph into a Zerg building anywhere on the Creep generated from Creep Colonies and Hatcheries, even when the creep is created by neutral or enemy buildings.
The Drone's armor, or Carapace, can be upgraded at the Evolution Chamber. The Drone, along with other Zerg units, can Burrow when the spell is researched at the Hatchery. Drones can also be built from the Lair and Hive; none of its properties and functions change regardless of where it is morphed.
Drones morph into buildings, and are consumed in the process. The building can be cancelled before completion to recover the Drone and the building's associated costs. This can be used to exploit a +1 supply with the Drone if the building is cancelled, thus potentially surpass the amount of supply a player has available. When cancelling a Zerg building, the Drone will also be restored to full health in case it had been damaged before, and it will also lose minerals/gas it carries. This can lengthen the life of a scouting Drone by morphing and canceling an Extractor in an opponent's base. Morphing a Drone will cancel a Defensive Matrix.
See also Basic Unit Commands
The Drone is primarily used to mine and morph into buildings. It is noted the Zerg must replace these Drones sacrificed for building production, as it can significantly impact the early game economy if they are not adequately replenished. Drones are also used to provide scouting, particularly in the early game. In ZvT and ZvP, the 9th or 12th drone are commonly used for scouting. In ZvZ, a drone scout is rarely sent out as this is a low economy match-up where it may be preferable to conserve this early Drone for mining minerals.
Drones can also be used to Drone Drill a defended ramp or choke. Sight is required on minerals past the chokepoint for this technique to work. Zerg players can opt to upgrade Burrow so they can have their Drones burrow when they are attacked by enemy units, particularly during drop play.
It is helpful to know how many Drones are needed to provide enough economy for a given number of Hatcheries. For example, nine Drones mining minerals will be sufficient to harvest enough minerals to produce the maximum amount of Zerglings possible from three hatcheries. Similarly, a total of 16 Drones mining minerals and gas is sufficient to produce mass Hydralisks from three Hatcheries.
Drones are sometimes used in Zerg vs Zerg to make offensive Creep Colonies on the opponent's Creep; this strategy must be coordinated with a simultaneous attack, as an unaccompanied Creep Colony morphing will easily be destroyed by the opponent. Drones are rarely used to scout in ZvZ, unless there is suspicion of a 4/5 Pool. Drones are particularly valuable in this match-up, so opponent Zerg forces will frequently target Drones during Zergling or Mutalisk attacks.
In the event of a Bunker Rush, Drones are particularly used to kill either the SCV building the Bunker, or the Marines that are attempting to enter the Bunker. This latter strategy frequently involves several Drones to be pulled from mining to exit the Zerg base so as to explore and block off any Marines before they arrive at the Bunker.
If a Terran chooses to go for a more aggressive early push, usually either immediately before or after the Terran has produced Medics, to break through the Zerg's Sunken Colonies, Drones can be pulled off the mineral line to further fight off the Marines, presuming they have not broken through. The best approach is to surround the Marines/Firebats/Medics while they are fighting the Sunken Colonies, as the Sunkens draw all their fire, thus enabling the Drones to attack them, unopposed. If the Drones are called off too late, they will be be easily destroyed.
Drones are very vulnerable to a Bio drop attack, so the Burrow ability can be effective in hiding the Drones before Zerg reinforcements arrive. Note the Terran can counter Burrow with Comsat Scan, so it may be preferable for the Zerg to pull the Drones away from the mineral line altogether.
In the case of a Cannon Rush, Drones are used to take down the Cannons before they warp in. This is vital as the Zerg player will frequently not yet have Zerglings or Sunken Colonies to fight off the early Cannons. On Fighting Spirit, where the Protoss player will frequently block off direct contact to the Cannon with Pylons, multiple Drones must be micro'd against a mineral patch to force it to pass through to the back of the mineral line.
In the event of Protoss aggression trying to break the Zerg's line of Sunken Colonies, the Drones can be called off the mineral line to help defend. Instead of trying to surround the units to deal damage, it is preferable for the Zerg to surround the Sunkens right before the Protoss charges in. This impedes melee units such as Zealots from getting immediately reaching, and thus attacking, the Sunken Colony, enabling the Sunken to deal some extra hits on the Protoss units as they scramble/walk around the Drones.
Drones are very vulnerable to a drop attack, such as Dark Templars, High Templars, or Reavers, so the Burrow ability can be effective in hiding the Drones before Zerg reinforcements arrive. Note the Protoss player can still use Psi Storm on the Burrowed workers, easily destroying them in one casting, so it may be preferable for the Zerg to pull the Drones away from the mineral line altogether.
Zergs can upgrade +1 armor so their Drones can endure two hits from a Dark Templar instead of one. This is particularly useful in the mid to late game as an non-upgrade Drone would die to one Dark Templar strike without the Zerg player being notified (i.e. "Your forces are under attack"). With two hits required, however, the announcement would be made along the Minimap flashing.