Donald Marshall (Thur. May 16, 2013) - Vrill have threatened at the cloning center to come up to the surface many times. But they'd lose badly. Small fast vrill type 1 would get the element of surprise and kill a lot of people but then humans would organize and blast them back underground and gas all tunnels leading deep.
But vrill are instinctually cowardly. They're literally parasitic life forms and the psychology of these things is cowardly. Hide in dark. Sneak attack. Attack in numbers. Only attack if ensured of victory. I learned as much about the vrill and all the other stuff as I could. To tell the world someday.
I'm very familiar with them.