I saw this in the 70s (75 maybe) at a drive in. Don’t remember much, but the hero figures out how to kill the monsters, which looked like floating snakes/sperm made out of light (I believe the effect was achieved by scratching the film, super low budget). Anyway the hero fashions some sort of rifle with a scope, perhaps shining a light on them to kill them, not sure, I was 5 or 6 when I saw it.