The motif of nature adds richness and sensuality, especially when it refers to the strong, emotional connection of the lovers. The motif of nature also adds an element of darkness and danger when it refers to the enmity that the lovers feel towards each other.
We see one instance of the motif of nature adding to the sensuality of the mood in the opening act when Theseus refers to the moon in relation to their wedding day. Theseus and Hippolyta represent the one couple that is in a solid relationship that is neither separated by circumstances nor by animosity. Theseus and Hippolyta are postponing their wedding day until the new moon appears as the new moon symbolizes a new beginning. Hence, Theseus is thinking of his sensual desires when he is reflecting on the current full moon in the opening act, as we see in his lines, "Another moon; but, O, methinks, how slow / This old moon wanes! She lingers my desires" (I.i.3-4). The reference to the full moon adds to the sensuality of the moment as the couple reflects on their feelings for each other because the reader/viewer can see the moon and hear the passion in Theseus's voice as he speaks his lines.
One instance of the motif of nature adding to the darkness and danger of the play can be seen when Demetrius is angered by Helena for having followed him into the woods and is threatening her. He is threatening her because he feels an intense sense of hatred towards her but also because he wants to provoke her to leave. We see him threaten her chastity and her safety in the lines:
You do impeach your modesty too much
To trust the opportunity of night,
And the ill counsel of a desert place,
With the rich worth of your virginity. (II.i.218-223)
Besides threatening to take serious advantage of her should she remain in the forest, he is also using dark nature references to frighten her. One nature reference is night, portraying the allusion of complete darkness surrounding the woods. A second nature reference can be seen when he calls the forest a "desert place." The image of the desert portrays just how empty and desolate the forest is, showing how dangerous it is for a vulnerable woman to be alone with a man in the forest whom she really should not trust. Hence, this nature reference calling the forest a desert captures for us the darkness and danger of the mood at this moment.