Significance The study of laboratory-generated circadian locomotor activity patterns of Drosophila played a critical role in determining how fruitfly (and mammalian) clocks function. However, recent observations of fly activity in the wild challenged many assumptions about how the clock might work. A new prominent summer locomotor component emerged called “A” (afternoon), which replaced the laboratory “siesta.” The A component has been criticized by others to be an artifact, but our study here shows that it is genuine and is observed under a variety of simulated natural conditions. The A component is temperature- and clock-dependent and is generated by expression of the internal transient receptor potential A1 thermosensor (TrpA1), revealing a pathway for environmental input to the clock.