The minimum temperature for flight is 54°F, and hive activity will increase when the temperature is consistently between 55°F - 60°F. However, the optimum temperature range for foraging is between 72 - 77°F. These temperatures typical coincide with when flowering plants are coming out of dormant states and being producing pollen and nectar.
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Hive activity declines when temperatures are over 100°F, and honey bees will usually stop flying to conserve energy.