Doreen Cronin's Diary of a Worm, Spider and Fly are silly tales about each of the respective animals. While the stories are far-fetched enough to garner lots of giggle, they are based on real attributes of each of the animals.
If you're looking to have your students do something a bit more creative than the traditional report after researching an animal, consider having them follow Cronin's model and write a "Diary of a _____".