Since spiders really aren't a trainable type of animal, the filmmakers used hairdryers to blow on them, in order to get them to move correctly.

Near the start of the film, when Atherton is examining the spider after returning from the valley, several butterflies are seen pinned up in front of him. Several of these are not South American butterflies - the top left one (blue with long tails) is Papilio Ulysses, a species of tropical Australia, and the big green-and-black one near the bottom right is Ornithoptera priamus or O. euphorion. Whether this qualifies as a mistake, I don't know - Atherton is supposed to be an expert, so they may not be the most geographically accurate 'colourful' butterflies to use.

The title of this movie comes from the clinical name for fear of spiders, arachnophobia. This name has its origins in Greek mythology. The goddess Athena got furious with a girl named Arachne over a weave she'd made which she claimed was better than anything Athena could produce. In her wrath Athena ruined the weave, and in her despair Arachne ran to the woods and hung herself. Athena felt bad about what had happened, so she found Arachne and gave her life again. She said that she would forever weave the most beautiful things, but people would seldom appreciate it or even notice it. She had turned Arachne into a spider. Arachnophobia, fear of spiders, fear of Arachne and her offspring. There are of course variations of this myth, but this is where the name for fear of spiders comes.