Time for making love. After the hard work of the harvest is done, and to relieve the pent-up tension of not being able to mate because of sweltering August weather (you know - sleeping on the porch, all the windows open, etc...). Also copulation at this time traditionally brought pregnancy to term after spring planting but well before the next year's harvest.
When the weather's hot and sticky there's no time for dunkin' dickie; when the frost is on the punkin that's the time for dickie dunkin'! - anonymous pithy verse
Tim was over to Laurie's again last night - I guess the frost is on the pumpkin!