The use of the moth metaphor by Earle Birney emphasizes the fact that the farmers of this community live their lives according to the natural rhythms of the year and the changing of the seasons. In a rural environment, the weather is king. And so, when the farmers venture out to town to socialize, it is only because the weather has allowed them to. Just as the moth can only emerge from the warmth and comfort of its chrysalis into the big old world outside when nature says it can, so the farmers can only venture forth from their homes when there's a let-up in the storm.
The artificial light of the town attracts the farmers as moths to a flame. Winter is approaching, and so there's precious little natural light during the daytime. In any case, as farmers they're incredibly busy during the day and so wouldn't have time for socializing. They go to the movies and then dance the night away. But the dance hall and the cinema must close, and so, without light and all it represents, the farmers must return to the safety and warmth of their homes, their "cocoons," waiting to "hatch" once more after the coming winter has passed.