Invasion of the Body Snatchers (1978 film)
"The plot centers around a doctor who discovers that the people of his town are being replaced by simulations grown from plantlike pods, perfect physical duplicates who kill and dispose of their human victims. The "pod people" are indistinguishable from normal people except for their utter lack of emotion. The pod people work together to secretly spread more pods—which grew from "seeds drifting through space for years"—in order to replace the entire human race."
from Wikipedia, http://en.wikipedia.org/wiki/Invasion_of_
Ya'll know what drones are.....