Continuity mistake: When Mrs Durant is swatting the bees off the table at the picnic site, you can see Mr Durant is holding a white plastic cup in his left hand. However, in a close-up of the table, you can see that the cup Mr Durant is holding has gone.
Other mistake: Fred MacMurray is listed as "Clarence" in the closing credits, but when he is standing outside his store and talking to Maureen, a promotional sign in the background spells his name as "Clarance."
Continuity mistake: After the bees attack the city, the dead are laid out in the town squire to be identified. They are lying uncovered. A few moments later a shot shows all of them in black body bags.
Continuity mistake: When the Marysville residents begin panicking in the carriage during the train evacuation scene, you can see that Olivia De Havilland isn't wearing her reading glasses, but in the next shot she has glasses on and takes them off again.
Continuity mistake: When Paul's mother is using a napkin to swat the bees off the table at the picnic site, she knocks over a white plastic cup, but when we see a full view of the table in the next shot, the cup has disappeared.
Continuity mistake: When Michael Caine is in the freezer in Mr Harris' café, he takes the thermometer and has his thumb on the blue line, but the next shot he is holding the thermometer with his thumb on the side.
Continuity mistake: When a larger group of soldiers enter the compound at the beginning of the film, the door of the compound opens to let them inside in one shot, but in the next shot the door is closed and opens a second time.
Irwin Allen was so disheartened by the amount of money he lost on this film that he forbade any of his employees to ever mention it again, and even cut short an interview when a question was asked about it.