Oversized reproductions of worms, chickens, wasps and rats were used to create the gigantic creature effect. Six different mechanized rat heads and four human-motivated rat costumes were also employed.
Many believe they actually shot rats (with something like pellet guns) for this movie. But if you look frame by frame, it is clear what is actually done is that they shot a high intensity squirt of fake blood, stunning the rat.
One of the rat costumes would later be reused for The Star Wars Holiday Special.
AIP's most successful film of the year.
Penultimate film for Ida Lupino. Her last movie, "My Boys Are Good Boys (1979)," would also co-star Ralph Meeker.