Climb up the water spout

Wouldn't you suppose that even a creature with a brain so small as that of a spider would, even off instinct alone, come to some sort of understanding that the monstrously gigantic moving mass of heat means *danger, run away*? It seems pretty basic.. even for an arachnid.. and yet they obliviously crawl onto people and right in front of people and etc, etc.. perhaps they lack the awareness that other beings even exist? Perhaps to a spider, there is no other intelligent life and the giant warm masses are as the weather. Perhaps WE are the spiders, so wrapped up in our own self-awareness that we fail to see the incomprehensibly larger beings waiting to crush us if we wander into their path.