what effect does summer have on the town?

Heat is a repeated motif of the story and is both realistic (because Florida, where the story is set, is indeed very hot in the summertime) as well as useful for setting the tone for the story. The heat is extremely oppressive, animals are going mad, and people are at their wits' end. It is in this tense atmosphere that Delia continues on working as she always does and Sykes finally crosses the line by bringing a snake to their house. In this way, it both underscores how hardworking and constant Delia is, and also suggests how difficult this time of year is for everyone.