Domesticated Creatures can be set to an aggression level to control their behavior. The aggression level can be changed in the select wheel when holding use (default E) near a creature or by whistle signals.
The following aggression levels are available:
The creature will try to run/move away if attacked. Creature stays where it stops after escaping. This skittish stance was added in patch v278.0.
The creature will not react to any attacks on it or anything else. Leaving your creature on passive can thus be dangerous, as Ants or other creatures can kill it.
The creature will only attack if it, a creature of the same tribe, or a structure of the tribe is attacked near it. This is probably the most useful aggression level.
Attack YOUR target
This aggression level is similar to Neutral, with the exception that the creature will attack any non-allied creature or player that another nearby allied creature, turret (not tested) or player attacks.
The creature will attack non-allied creatures and players near it. Leaving a creature on aggressive can let other creatures or players (in PvP) lure them away.