Myth Library · Transformation
Io, Argus, and the Gadfly
1 source witness · 1 source-scoped variant · reviewed 2026-08-30
Pseudo-Apollodorus tells how Io becomes a cow, Hera sets Argus to guard her, Hermes kills the watchman, and Hera’s gadfly drives Io across distant lands.
Canonical narrative
Pseudo-Apollodorus begins with competing genealogies for Io, naming her either daughter of Iasus or, in other accounts, of Inachus or Peiren. Zeus has sex with her. When Hera arrives, Zeus changes Io into a white cow and denies the encounter. Hera asks for the cow as a gift. Zeus cannot refuse without exposing the deception, so Io passes into Hera’s keeping.
Hera appoints Argus Panoptes as guard. The many-eyed watchman binds the transformed Io to an olive tree in a grove at Mycenae. Zeus sends Hermes to steal her away. When secrecy fails, Hermes kills Argus with a stone, earning the title Argeiphontes within the mythographer’s explanation.
Hera’s pursuit does not end with the guard’s death. She sends a gadfly against the cow, and Io flees across the Ionian Gulf, Illyria, Haemus, Scythia, the Cimmerian Bosporus, and onward until Egypt. There Zeus restores her human form, and she bears Epaphus. The mythographer uses the wandering body to explain place names and connect Greek genealogy to Egypt.
Io is the person most harmed by the sequence. Hera’s anger, Zeus’s concealment, Argus’s confinement, Hermes’ killing, and the gadfly’s torment should not be retold as a decorative love triangle. The source preserves variant parentage and a long geography of coerced transformation.
Episodes in this myth
Episode 1
Io becomes Hera’s cow
Zeus transforms Io into a white cow, and Hera obtains the animal as a gift after challenging his concealment.
Episode 2
Argus guards Io and Hermes kills him
Argus confines Io in the Mycenaean grove until Hermes kills the guard with a stone.
Episode 3
The gadfly drives Io abroad
Hera sends the gadfly that drives the transformed Io across a long itinerary toward Egypt.
Participants and roles
Hera
Takes custody of Io, appoints Argus, and sends the gadfly
Pseudo-Apollodorus Library book 2, chapter 1, section 3: takes custody of Io, appoints Argus, and sends the gadfly.Io
Transformed and pursued central figure
Pseudo-Apollodorus Library book 2, chapter 1, section 3: transformed and pursued central figure.Zeus
Transforms Io and sends Hermes
Pseudo-Apollodorus Library book 2, chapter 1, section 3: transforms Io and sends Hermes.Argus Panoptes
Guard appointed by Hera
Pseudo-Apollodorus Library book 2, chapter 1, section 3: guard appointed by Hera.Hermes
Kills Argus and frees Io
Pseudo-Apollodorus Library book 2, chapter 1, section 3: kills Argus and frees Io.Gadfly
Instrument of Io’s continuing torment
Pseudo-Apollodorus names the gadfly as the living torment that drives Io onward; it is not an object.Source-scoped variants
Io, Argus, and the Gadfly in Pseudo-Apollodorus
Pseudo-Apollodorus joins Io’s variant parentage to her bovine transformation, confinement under Argus, rescue by Hermes, and gadfly-driven journey.
What differs: The mythographer preserves multiple fathers for Io and an expansive itinerary rather than choosing one seamless genealogy.
Greek Roman Imperial · ArgosSource witnesses
EXPLICIT PRIMARY · Reviewed
Library
Pseudo-Apollodorus; edited and translated by James G. Frazer · 1921
Book 2 · Chapter 1 · Section 3
Io, Argus, and the Gadfly is retained as a source-bounded telling from the exact cited passage; later syntheses do not replace it.
Open reviewed source