Primitive Aliens with the IQ of a hamster on crack invade earth...
...to consume human flesh? Really??? How did that get green lighted?
shareWell, not. They were a biological weapon being transported by unknown alien ship that crashed in earth and got loose after the ice holding them melted. They consume all flesh (as shown in the helicopter ride where they chase down and eat zebras). They were presumably designed by some alien race to only eat and multiply thus overwhelming any planet this "weapon" was used on.
Their intelligence seems to be good enough to act like a hive and coordinate large group attacks. The females also seem to be smart enough to hold a grudge on the doctor.