The character of Zeus is well-known for seducing many women, both human and goddesses. In many of these stories, Zeus assumes a form other than his true self.

The most famous is perhaps Leda - it is said that Zeus seduced her in the form of a swan (some versions specify that he came to her, in swan form, seeking protection from an eagle).

However, there are many other stories - this page lists several lovers who were not seduced in human form:

ANTIOPE: A Lady of Thebes in Boiotia (Central Greece) who was seduced by Zeus in the shape of a satyr. She bore him twin sons Amphion and Zethos which were exposed at birth. DANAE: A Princess of Argos (in Central Greece) who was imprisoned by her father in a bronze tower. Zeus seduced her in the form of a golden shower, and she gave birth to a son, the hero Perseus. EURYMEDOUSA: A Princess of Phthiotis (in Northern Greece) who was seduced by Zeus in the form of an ant. Their son was named Myrmidon (Ant-Man). LEDA: A Queen of Lakedaimonia (in Southern Greece) who was seduced by Zeus in the form of a swan. She laid an egg from which were hatched the Dioskouroi twins PHTHIA: A girl from Aegion in Akhaia (southern Greece). Zeus seduced her in the guise of a pigeon or dove.

In some stories, it makes complete sense why Zeus assumed the form he did:

ALKMENE: A Lady of Thebes in Boiotia (Central Greece) who was seduced by Zeus in the form of her own husband. She bore twins: Herakles by Zeus and Likymnios by her husband Amphitryon.

The story of Semele, Dionysus' mother, explains why Zeus does not present himself in his godly form - mortals perish when they look upon gods. However, it doesn't really explain why Zeus chose such varied, non-human, and frankly weird (ant?!), shapes for his seduction process. My question is, do any stories every offer an explanation for Zeus' shapes, or an indication of the motivation behind it?