They don't need to. Know what makes a REALLY annoying sound, even to me? High tension wires. So... everywhere there are monsters, power is gone. These things do NOT need to beat any organized military. They just need to disrupt power and supply lines. Which they would be quite good at. They are completely immune to small arms fire... so think to yourself. If one appeared on my street right now... how long until a fifty caliber got here? We only have so many troops. And they need to eat just like the rest of us. Anywhere there isn't some big guns, the power is gone. No food or fuel is being delivered. The waves of starvation, disease and unrest from the toppling of our fragile technological society would most likely kill far more of us than the monsters did. They just rocked the apple cart.