Originally the spiders in the film were suppose to be only about 10 feet in length but the producers insisted that if the film were going to compete with Jaws (1975), which was released around the same time, the size of the spiders would have to be increased to pose more threat.
There was supposed to be a dramatic shot of the giant spider crushing the house by having the spider dropped from a crane onto it while a bulldozer chained to the back of the house would pull away. However, when the shot was filmed, the spider's legs all went straight up into the air! The crew inside working it's arms were nearly killed when broken wood from the demolished house went through the spider, coming close to impaling them.
There was supposed to be a shot of a big spider in a tree bursting into flames. To achieve this, the director covered a large prop spider with gunpowder and had two crew members sitting above it in the tree who would drop a match on the spider. The director got the camera up to a very fast fps to achieve a slow motion look, and had them drop the first match. Nothing happened, so they dropped a second. Still nothing happened, so they lit the entire book of matches and dropped it on the spider. With nothing happening, the director turned off the camera - and immediately afterwords a huge explosion and fireball shot up, burning the hair off of the crew members and starting several small brush fires. The director was furious that he wasn't able to get the shot on film.
Dan and Ev have a conversation which includes the exchange: Ev: "I'm sorry I missed the sermon. What was it about?" Dan: "Sin." Ev: "What did the minister say about it?" Dan: "He was against it." That referred to a famous (or infamous) conversation former President Calvin Coolidge - nicknamed "Silent Cal" - and his wife once had.
According to Bill Rebane the two writers on the film each approached the story from different directions. Richard L. Huff wrote the original story and kept a very serious tone to the first draft of the script. Robert Easton on the other hand lent the film a comical tone, writing most of the colorful dialog for his character and the other locals. The films rather infamous jokes are credited to him as well. Combining both writers material resulted in an odd-ball tone for the script.
In May 2005 there was a Bill Rebane film festival in Madison, Wisconsin that featured this film. Hosting the festival were Michael J. Nelson and Kevin Murphy of the TV series Mystery Science Theater 3000 (1988), which featured The Giant Spider Invasion in a 1997 episode. Nelson and Murphy said despite their lampooning of the film on MST3K they actually admired Rebane because he was able to make the film with such a low budget.