Bats have been featured twice in Calvin and Hobbes. Calvin appeared as a bat alter ego in a single weekday strip and did an oral report on bats in a story arc.
10/27 through 11/4 1989 story arc
Calvin did a report on bats for school in this 1989 story arc. In it, he exposed his dubious knowledge of bats (he firmly believed them to be bugs). As he had done no research, he opted for a dramatic, sensationalistic speech highlighting the terrifying aspects of bats. Also, his scientific illustration was a copy of the Batman logo with fangs added. Calvin ultimately failed the assignment.
Alter ego
Calvin appeared as a bat alter ego in a single weekday strip where it consumed an insect by radiolocating its position and eating it whole. The alter ego was analogous to Calvin throwing food into his mouth with his eyes closed at a restaurant.