they destroyed themselves... most probable bet, maybe there are few still alive, but they are so prudent, now... unless they forgot... what ever.... let's stay focused and not distracted, if an alien space fleet comes to harvest human brains that they grow on earth naturally (ie with taste), what will be able to do? if they come every single human... they will be able...

anyway, don't forget their first contact was laika... not a good image... and who knows they maybe cloned it, teleported her back to the fleet... who knows... it sounds crazy? like going to moon maybe?