We know the mimics overran the entirety of the European Union, or at least the vast majority of it. However throughout the movie we never see or hear of any survivors living in occupied areas, did the mimics just wipe out pretty much everyone they encountered?
It took them five years to take control of the subcontinent, so either everyone there is evacuated or dead of all kinds of causes. And yes, mimics did kill everyone they've met.
When you listen to news at the beginning of the movie there is a voice saying:
"(...) when they landed on Earth, five years ago, their (...) advance across Europe was unstoppable (...) millions of victims (...) continued evacuation (...)".
Simultaneously it shows landing site and then - in red - expansion of area they controlled. At least I assume as much - red is traditionally used by NATO to mark enemy units/position/controlled territory.
5 years is impossible to survive in territory where enemy is of different species, with ability to move under ground, under water and quite a long ways in air. And where almost all humans are gone. Also, 5 years to conquer Europe is excessively slow, even with constant fighting, so it definitely suggests "weeding".