Theseus asks Achelous how he lost half of his power. Achelous is reluctant to tell a story of his own defeat but begins: Achelous falls in love with Deianira, who has countless suitors. Achelous enters Deianira’s father’s palace and asks for Deianira’s hand in marriage. At the same time, Hercules asks Deianira’s father the same thing. Hercules explains that Jupiter is his father and that he has performed many tasks at his stepmother Juno’s request. Achelous retorts that if it is true that Hercules is Jove’s son, he is also a bastard and the result of the god cheating on his wife.
The contest between Hercules and Achelous is another example of the divisive potential of love. Hercules and Achelous butt heads over their mutual love for Deianira. Moreover, Achelous insults Hercules by pointing out that his existence is the result of a divisive love story: if Hercules is a god, then he is also the result of an affair. In this way, love is a divisive force that can also affect a person’s identity long after they are born.
Angry at this accusation, Hercules says that Achelous can win with words, but he, Hercules, can win with physical strength. Hercules and Achelous start to wrestle. After a long fight, Hercules grips Achelous’s throat and brings him to his knees. Achelous transforms into a snake and slithers from his grasp. Hercules taunts that Achelous can’t really use the powers of a serpent, because it is only a disguise and not his natural form. Hercules again grips Achelous’s throat. To escape, Achelous turns into a bull. He lunges at Hercules, but Hercules pushes him to the ground, grabs one of his horns, and wrenches it off.
This passage points out that, while the gods can change form, they are not rendered entirely all-powerful by doing so. When a god transforms, they are not able to make use of the strengths of that particular animal, meaning that their self-transformation is limited. This reveals that the gods are of a different order than humans, animals, and nature: while the latter three are easily transformed into each other, the gods can only disguise themselves.
As Achelous finishes the story of his defeat, a nymph comes in bearing Achelous’s broken horn filled with fruit for the guests. The next morning, Theseus and his companions leave, not wanting to wait any longer for the flood to go down.
Theseus and his companions leave somewhat abruptly, suggesting that they are not in awe of Achelous—who was defeated by a half-god—nor do they venerate him.