It Conquered the World (1956)

The archetypal Roger Corman science fiction B-movie, It Conquered the World (1956) features a typically small scale alien invasion from Venus that in noway justifies the grandiose title, (which Corman doubtless sold the film to financiers with).  The film is undoubtedly most famous for its monster, a sort of perambulating giant cucumber with a face, (or rather half a cucumber as it appears cut off at the waist and has no visible legs), which is the vanguard of an alien invasion.  Naturally, it immediately hides out in a cave near a small town and army base and sets in motion its plan, which involves mind control of key citizens via bat-like flying parasites.  It is aided by naive and idealistic scientist Lee van Cleef (in an early role), with whom it has been in radio communication prior to its arrival.  Obviously, he's the sort of dupe who, if this was a cold war propaganda movie, would fall for the commie rhetoric put out by Soviet agents.

Luckily for the earth, though, this a low budget film, so not only are there only seven more of these creatures waiting to invade from Venus, but the one already on earth can't manufacture more than eight of those parasitic mind control things.  Despite the local General succumbing to Venusian mind control early on and sending the local military force off on unscheduled manouevres, they figure out something is wrong and eventually surround that cave.  All ten of them, (it's a low budget movie, don't forget).  But it still takes van Cleef's colleague, red blooded, two-fisted,  all-American scientist Peter Graves to put paid to the giant cucumber with a blow torch.  The film was allegedly shot in ten days and looks it but, like most Corman pictures, it is curiouly entertaining.  At only sixty nine minutes it moves at quite a pace, leaving little time to worry too much about its absurdities while it is playing.  It is also surprisingly ruthless - the characters taken over by the Venusian, including Graves' wife, are apparently beyond hope as summarily dispatched - Corman isn't interested in delivering happy endings to any character in this film, no matter how sympathetic they might be.   Which gives the film something of an edge compared to other, similar, B-movies of the era.