Why would the bees think that the warm days will never end in "To Autumn"?
The first stanza of Keats's "To Autumn" describes the point of transition between summer and autumn. The fruit is ripe and ready to fall, and the bees have enjoyed the sun of summer for so long that "they think warm days will never cease." Most bees live for only a matter of weeks and so will not be familiar with the cycle of the seasons. This is perhaps why they believe that summer will never end, because summer is all they have ever known.
In the next line, Keats offers another reason to explain why the bees thought that summer would never end. He says it's because "Summer has o'er-brimmed their clammy cells." This is a reference to the bees' honeycombs, which are at this point of the year full of honey. For the bees, perhaps their "warm days will never cease" because those warm days have helped them to produce so much honey. In other words, while the warm days may literally disappear, they will live on in the form of the honey that they have helped the bees to produce.
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