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.
Penultimate film for Ida Lupino. Her last movie, My Boys Are Good Boys (1978), would also co-star Ralph Meeker.
British actress Pamela Franklin's last feature film, although she would continue to work in television on several guest starring roles.
Though it's said to be adapted from H.G. Wells, the plot of a man (in this case, an elderly couple) with food that makes animals gigantic (including a rooster) in order to one day feed the world's hungry, comes from the Jules Verne adaptation, Mysterious Island (1961) (famous for the stop-motion effects by Ray Harryhausen).
AIP's most successful film of the year.
Ray Harryhausen was interested in making this film.
This movie has been featured in the German television show, "Die schlechtesten Filme aller Zeiten" (The worst movies of all time) where two hosts show the movie while making fun of it.
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.