Drone

Overview
The drone is the Zerg worker unit. Drones stem from the savage gashyrr wasps of Eldersthine, absorbed into the Zerg Swarm to serve as resource gatherers. Over time they became drones, engineered with the larvae's ability to break down their own genetic coding and transform themselves into rudimentary zerg structures. A transforming drone needs creep to provide nourishment and mass to support its new form. Like the larva, drones are controlled by overlords who monitor their progress. Drones are usually single-minded about their tasks, diligently working through even raging combat. Drones possess limited combat ability, but in a swarm, they can present a significant threat, attacking with claws and spines.

Information
Drones "mutate" into the buildings they construct. The only way to stop a building from completing is to destroy it or to cancel it; in the latter event the drone is recovered and may be used for some other purpose. Once the building is complete the drone is permanently lost. Drones benefit from burrow. Unless the enemy brings detectors burrowing can minimize the damage caused by a raid on harvesting operations. Once the enemy is repelled harvesting may immediately resume without requiring the replacement of all workers. In earlier builds of StarCraft II, drones were not required to build defensive structures, such a role having been taken over by the queen.[11] Drones have regained their ability to create defensive structures.