Don't forget that you need to write in first person narrative. First person narrative means writing from the "I" point of view. "As I slithered along the jungle floor, my eyes were darting back and forth in search of food." 
You must pretend that you are the animal and describe where you live, what you look like, how you move, what you eat and any other important fact that you learned about your animal from your research.
Use OPAC to find these books in the Library Media Center They are written in first person narrative.
The Diary of a Spider by Doreen Cronin
The Diary of a Worm by Doreen Cronin
The Diary of a Killer Cat Notso Hotso by Anne Fine