For some reason, when I move up or down to another level on the terrain, my spiderant will follow, triggering its cool-down timer for attack commands. The other two pets don’t seem to do this.
When the spiderant follows me it “spawns” from the ground.
And now that I’m looking at the skills, I think it is triggering the “Spiderant Countess” ability, which would explain the cool-down and the corrosive explosion.