The original post's trailer is no longer is available, but I think this one might be more fun. It's one of my favorite early Corman movies. I saw it at the perfect age of about nine or ten years old in the middle of the night. Movies like this are a lot scarier then, I'll tell you what.
This trailer has Roger Corman introducing it to the fans. He gives a little background and then it launches. What a fun movie, and these are true monsters (unlike most of the merely giant animals in US movies).