Watch for the guitarist for the group The Birds at the beginning of the movie - it's a pre-Faces, pre-Rolling Stones Ron Wood. He's on the far right of the screen.
The exteriors of the Hargrove farm were built entirely on sound stages, complete with fake trees, fences and sheds.
The special effects for the bee attack sequences were quite simple. Often footage of swarming bees would be superimposed over footage of the actors and fake plastic bees would be glued to the actors. Some shots of swarming 'bees' was actually footage of coffee grounds, floating and swirling in water tanks, that was superimposed over landscape footage.
Widely considered the first killer bee film ever made.
For the role of H.W. Manfred, Frank Finlay was made to look older with makeup. His hair was also dyed gray.