Organisms on earth evolved a circadian clock that matches the planet's 24-hour rotation. The plant clock controls many behaviors and proper entrainment of the clock to the environment leads to a competitive overall growth advantage. Despite the finding that many wound-inducible genes are also circadian regulated, it was uncertain whether this regulation is important for plant defense against herbivorous insects. We found that plants entrained to light-dark cycles 12 hours out of phase with the predator, Trichoplusia ni (cabbage loopers), were more susceptible to T. ni herbivory than plants entrained in phase with T ni . In contrast, arrhythmic clock and jasmonate-deficient mutants were equally susceptible to T. ni herbivory whether entrained in the same or reciprocal 12-hour light-dark cycles. These results suggest that the circadian rhythms, acting through jasmonate signals and the clock, add selective advantage to plants through enhanced anticipation of and defense against herbivory.