The Spine crawler is a mobile zerg defensive structure. It replaces the sunken colony as the zerg's primary anti-ground defense structure in StarCraft II. The spine crawler's tentacle can stretch nearly twice its height and slam into ground targets.
Spine crawlers are ground defensive structures that can uproot and relocate. They can only plant themselves on the creep. The spine crawler will stop rooting itself if the creep under it recedes during the rooting animation.
Like the spore crawler, the spine crawler will slowly die if rooted in ground not covered with creep. They can, however, survive indefinitely without creep as long as they are uprooted.
Players will want to spread creep onto the map to create more space for their crawlers, such as putting creep onto choke points. The ability to mobilize base defense also allows for new streamlined strategies that would call for less units, as they can be redistributed across the base depending on the situation. They can be used offensively, moving them forward with the creep as either fall back position or a long ranged attack unit (something which the zerg generally lack), depending on where the enemy attacks.
Crawlers can uproot themselves from the creep and move about, but can only plant themselves back onto the creep. They move much more quickly on the creep than off it.
Heroes of the StormEdit
The following section contains information from a previous version of StarCraft II which is no longer valid.
The concept of mobile defenses in StarCraft II began with the phase cannons, but was transferred to spine and spore crawlers when the phase cannon proved to be unbalanced in testing. Prior to this, crawlers were stationary structures. They underwent a visual re-design late in the game's development cycle.
In StarCraft II: Heart of the Swarm, the spine crawler gained was made larger (a collision size of 0.95), allowing it to block pathing of small units such as zerglings that try to pass between them and other buildings.