Teenagers from Outer Space

Teenagers from Outer Space released as The Gargon Terror in the UK and originally titled The Ray Gun Terror is a 1959 independently made American blackandwhite science fiction film released by Warner Bros. Pictures. The film was produced, written, and directed by Tom Graeff and stars David Love, Dawn Bender, Bryan Grant, Harvey B. Dunn, Tom Graeff, and King Moody.

An alien spaceship comes to Earth while searching for a planet suitable to raise Gargons, a lobsterlike but airbreathing creature that is a delicacy on their home world. Thor Bryan Grant shows his alien contempt for Earths creatures by vaporizing a dog named Sparky. Crew member Derek David Love, after discovering an inscription on Sparkys dog tag, fears that the Gargon might destroy Earths native inhabitants. This makes the other aliens scoff at the thought. Being members of the supreme race, they disdain foreign beings, no matter how intelligent they pride themselves that families and friendships are forbidden on their world. Derek turns out to be a member of an alien underground that commemorates the more humane periods of their worlds history.Their one Gargon seems to be sick in Earths atmosphere. While his crew mates are distracted, Derek leaves. Eventually, the Gargon seems to revive. When the Captain reports his actions, Derek is quickly connected to their Leader Gene Sterling Derek, it turns out, is the Leaders son, although Derek is unaware of this. Thor is sent to hunt down Derek, with orders to kill him in order to protect their mission to Earth. They return to their base, leaving the Gargon behind. ........

Source: Wikipedia