Eroticism in the language of beasts permeates Midsummer in a strange undercurrent—a motif-- that parallels but also subverts the traditional notion of love that the play finally celebrates. Interestingly, this eroticism between the animals consistently crosses species. We see this in numerous examples: Titania's infatuation with the Bottom (who is an ass); through Helena's passionate plea to the disdainful Demetrius, "I am your spaniel, and, Demetrius, / The more you beat me I will fawn on you. / Use me but as your spaniel"; to Bottom's histrionic desire to act the roles of both Thisbe and the Lion in "Pyramus and Thisbe" (I.ii.43-45; 58-60); to Puck's reassurance to the young lovers that "Jack shall have Jill, / Nought shall go ill; / The man shall have his mare again, and all shall be well" (III.iii.45-47).

Eroticism is a motif, perhaps, but not so much a theme in the play because Shakespeare makes no real statement or message about eroticism. As a motif it is chiefly relected through Hippolyta and Bottom, Hippolyta and Oberon; to a lesser extent through the lovers Lysander, Demetrius, Helena and Hermia; and, when Puck is played by a female, it opens up some fun choices between Puck and Oberon which might support the motif.

It is a motif because there are elements of wild, reckless love / lust throughout the play. But I would hesitate to call eroticism a theme in the play.