Help Identifying a Science Fiction Movie

Question

I'm looking for the name of a movie from the 1950s. It involved an alien race that put a forcefield around a major city (Maybe LA) and some survivors were stuck inside. The most identfying thing I can remember is that the aliens used spears and one of the heroes discovered that if he knocked the tip off and stabbed one of the aliens with the hollow shaft its own body pressure forced its blood out through the spear and killed it.

Answer 1

It could be Invasion 1965

From vicpine.co.uk:

Aliens put an invisible force field around a secluded country hospital in this endearingly daffy British oddity, which must feature the cheapest alien takeover in history. Edward Judd is the hero scientist battling the extraterrestrial Oriental women in spacesuits, in an efficiently made and, yes, mildly exciting slice of cut-price science fiction.

Answer 2

The movie is The Slime People (1963). The hollow-shaft impalement scene is at the end of the trailer.

From the Wikipedia entry:

The film concerns a race of subterranean reptile-men (dubbed "slime people" due to their slime-covered skin) who create a wall of "solidified fog" around Los Angeles and proceed to invade the city.

The image that sticks with me is that of the contorted dead man, still standing, that the heroes find embedded in the solidified fog.