The gadfly, a type of fly plaguing cattle, typically ones belonging to either the family Tabanidae (horse-flies

Horse-fly

Insects in the order Diptera, family Tabanidae, are commonly called horse flies. Often considered pests for the bites that many inflict, they are among the world's largest true flies. They are known to be extremely noisy during flight. They are also important pollinators of flowers, especially in...

) or the family Oestridae (bot flies

Botfly

A botfly is any fly in the family Oestridae, which includes all the members of the former families Cuterebridae, Gasterophilidae, and Hypodermatidae. It is the only family of flies whose larvae live as obligate parasites within the bodies of mammals, with the exception of a few screwworm flies in...

), appears in Greek mythology

Greek mythology

Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

 as a tormenter to Io

Io (mythology)

Io was, in Greek mythology, a priestess of Hera in Argos, a nymph who was seduced by Zeus, who changed her into a heifer to escape detection. His wife Hera set ever-watchful Argus Panoptes to guard her, but Hermes was sent to distract the guardian and slay him...

, the heifer maiden. Zeus

Zeus

In the ancient Greek religion, Zeus was the "Father of Gods and men" who ruled the Olympians of Mount Olympus as a father ruled the family. He was the god of sky and thunder in Greek mythology. His Roman counterpart is Jupiter and his Etruscan counterpart is Tinia.Zeus was the child of Cronus...

 lusts after Io and eventually turns her into a white heifer to hide her from his jealous wife, Hera

Hera

Hera was the wife and one of three sisters of Zeus in the Olympian pantheon of Greek mythology and religion. Her chief function was as the goddess of women and marriage. Her counterpart in the religion of ancient Rome was Juno. The cow and the peacock were sacred to her...

. Hera is not fooled, and demands Io as a gift from Zeus. She then sends Argus

Argus Panoptes

In Greek mythology, Argus Panoptes or Argos, guardian of the heifer-nymph Io and son of Arestor, was a primordial giant whose epithet "Panoptes", "all-seeing", led to his being described with multiple, often one hundred, eyes. The epithet Panoptes was applied to the Titan of the Sun, Helios, and...

, the 100-eyed monster to guard Io. Hermes, (ordered by Zeus), kills Argus. When Hera finds out that Argus has been killed, (causing heifer Io to become loose), later sends the gadfly to torment and sting Io, forcing her to wander farther and farther away from home.

The gadfly also plays a role in the myth of how Bellerophon

Bellerophon

Bellerophon or Bellerophontes is a hero of Greek mythology. He was "the greatest hero and slayer of monsters, alongside of Cadmus and Perseus, before the days of Heracles", and his greatest feat was killing the Chimera, a monster that Homer depicted with a lion's head, a goat's body, and a...

 loses Pegasus

Pegasus

Pegasus is one of the best known fantastical as well as mythological creatures in Greek mythology. He is a winged divine horse, usually white in color. He was sired by Poseidon, in his role as horse-god, and foaled by the Gorgon Medusa. He was the brother of Chrysaor, born at a single birthing...

. Bellerophon attempts to ride Pegasus to the top of Mt. Olympus. Zeus is enraged by the human's attempt to ascend to the home of the gods. He sends a gadfly to sting Pegasus. The winged horse is startled and he rears backward. Bellerophon loses his grip and falls back to Earth. Athena

Athena

In Greek mythology, Athena, Athenê, or Athene , also referred to as Pallas Athena/Athene , is the goddess of wisdom, courage, inspiration, civilization, warfare, strength, strategy, the arts, crafts, justice, and skill. Minerva, Athena's Roman incarnation, embodies similar attributes. Athena is...

spares his life by causing him to land on soft ground, but he becomes blind and wanders the earth until he dies, being hated by men and Gods. Bellerophon never finds Pegasus again .