Zeus was a jealous god, prone to acts of deception in order to seduce beautiful gods and mortals, and he was not pleased with Eos's infatuation with a rival. In a classic Devil's Bargain, he granted Eos's wish -- literally. He made Tithonus immortal, but did not grant him eternal youth.

As Tithonus aged, he became increasingly debilitated and demented, eventually driving Eos to distraction with his constant babbling.

In despair, she turned Tithonus into a grasshopper. In Greek mythology, the grasshopper is immortal. (In a close cultural parallel, the Chinese believed that locusts live forever). This myth also explains why grasshoppers chirp ceaselessly, like demented old men.