Bug is a 1975 American horror film directed by Jeannot Szwarc and written by William Castle and Thomas Page, from Page's novel The Hephaestus Plague (1973). Shot in Panavision, it was the last film Castle was involved in before his death in 1977. The film starred Bradford Dillman, Joanna Miles and Richard Gilliland.

The film initially depicts a new insect species, which faces extinction. A widowed scientist crossbreeds the species with cockroaches, creating a sentient hybrid species of insects.