In the evolution of Galactic Overlord technology they may have traded massiveness for speed. With the minimal mass of virii they can approach the speed of light with a lasar push most efficiently. They are slower than massless photons and neutrinos but not by much. For such small craft they are a big problem for our galactic neighbors like the Dropa, Greys and Giants. Our best defense against G.O.'s has been our average spider that can eat them whole.