Answer: The speakers of both "To a Butterfly" and "Sonnet to the River Otter" suggest that the natural world, and its creatures, help shaping fond and longed-for memories, and rendering them clear as time goes by. Nature was a prominent theme in Romanticism. The natural world was praised and embraced for its ability to help people trascend their everyday lives and find solace and a new meaning to their otherwise alienated existences.
Explanation: In "To a Butterfly" the speaker's unhurried encounter with a butterfly in a charming natural setting brings him extremely pleasant memories of his childhood, and he is so thrilled that he begs the little creature not to "take the flight" and stay near him. The sight of the butterfly has immediately helped him to remember days that brought him joy, joy that, perhaps, he has not been able to experience since then. In "Sonnet to the River Otter" the speaker also recalls sweet childhood memories by the river at his native town, and he wishes he could be, once again, the "careless child" he used to be back then. The close encounter with, and experience of, the natural world is also here helping the speaker to recall enriching memories from the past and to arguably break away from a reality that, unlike that of his childhood, is only partially satisfying.