The Mothra larva was the largest costume Toho would create in the Showa era. The Mothra larva seen rampaging through Tokyo's neighborhood was about 7 feet tall and just over 31 feet long. Weighing about 265 pounds (120 kilograms), a total of eight actors were needed to perform and operate the Mothra larva.
The film was based on a short fantasy novel called "The Luminous Fairies and Mothra" (Hakko Yosei to Mosura). Toho commissioned the story, wanting to appeal to a female audiences since Toho president/producer Iwao Mori found that women made up a large portion of the movie-going public and would often bring people along with them. Writers Takehiko Fukunaga, Shin'ichirô Nakamura, and Yoshie Hotta each wrote part of the original story which was then adapted by screenwriter Shin'ichi Sekizawa into the final film. The film was a hit at the box office and became one of Toho's most successful fantasy films, with Mothra becoming a popular character who would star alongside Godzilla as well has her own film series decades later.
Martin Scorsese has expressed admiration for the imagination of this and other Toho science fiction/fantasy films directed by Honda, having written the foreword to the director's biography.
Rolisica serves as a hybridized stand in between the United States and the Soviet Union, the name of the nation being a hybrid of the Japanese pronunciation of Russia and America. The original name was Roshirica and the Rolisican flag is a hybrid of the American "Stars and Stripes" and the Russian "Hammer and Sickle". Screenwriter Sekizawa however wanted Mothra to actually attack New York City. His idea however was shot down and after some deliberation he had to make due with the fictional New Kirk City as a stand in instead.
With some additional funds from Columbia Pictures, Mothra not only became Toho's most expensive film ever made up until that point, but also being the most expensive film ever made in Japan at the time.