The gadfly, a type of fly, known for plaguing cattle, appears in Greek mythology as a tormenter of Pegasus and Io, a human lover of Zeus.
In the story, Zeus lusted Io, who is eventually turned into a white heifer to hide her from his jealous wife, Hera.
When Hera finds out, she sends a gadfly to torment and sting Io, forcing her to wander further and further away from home.
The gadfly plays a role in the myth of how Bellerophon loses Pegasus and the gods' favor.
Athena spares his life by causing him to land on soft ground, but he becomes blind and wanders the earth alone until he dies, hated by both men and gods.