Well acted but slightly dull science fiction, sort of Quatermass in a minor key, though the plot is more reminiscent of The Day the Earth Stood Still, minus that film's shrill, hectoring tone. An oddly neglected film, though it does have several flaws-- too many romantic subplots, for example. The sudden lurch into action mode in the last reel disrupts the pacing and atmosphere, as well. The indulgently gory shot of giant bugs munching on a soldier's face is a bit surprising for the time frame! The effects (by Les Bowie) are better than the Bert I. Gordon/50s average, though obviously dated. Still deserves to be more well-known than it is, and it is a pleasure to see Mango and Benson in fairly large roles for once. The latter's interstellar Orkin man is particularly good.

Based on a 1956 television serial by actress Rene Ray, which was novelised the next year. US posters show the title as Cosmic Monsters, but the title shot (at least on TCM prints) reads The Cosmic Monster.

Thanks to philly for identfying several unknowns!