Many zerg ground units may burrow, become invisible and may be revealed primarily by detectors, and may not move or attack. Exceptions are the roach, which may move while burrowed, the infestor, which may move and cast Infested Terran, and the baneling, which can detonate while burrowed.
Some units can unburrow via autocast, causing them to emerge and attack when an enemy moves into range.
The following section contains information from a previous version of StarCraft II which is no longer valid.
In earlier builds of StarCraft II, drones were not required to build defensive structures, such a role having been taken over by the queen. Drones have regained their ability to create defensive structures.