The main characters in a bug's life story could be different depending on the focus of the story. If it's a story about a spider, then the spider is the main character. It might also include the insects that the spider catches in its web as part of the story's plot, as they are related to the spider's survival and hunting activities.
In many bug's life stories, there are often the bugs as the main characters. For example, in a story about a bee, the bee would be a main character. It could also include other bugs that interact with it, such as the flowers that the bee visits, which could be considered secondary characters that are important to the bee's story.