Burrow
Source: Hatchery
Minerals: 100
Vespene Gas: 100
Research Time: 80
This ability is available to several Zerg grounds units including the Zergling. A burrowed unit will dig itself into the ground rendering it invisible and cannot be attacked unless a nearby detector unit can spot its location. The burrowed unit cannot attack any units, but it can see a very small distance. This ability is great for hiding your injured units to allow them to recover health or for spying at certain locations, such as expansion points or outside enemy bases to track enemy movement. Since Zerglings are relatively cheap, it is common to send several of them out to important areas of the map and keep them burrowed.