The robber fly, Promachus yesonicus, a predator of scarab adults and larvae was observed on golf clubs in Korea to determine its seasonal activity, daily activity, and relationship to scarab adult activity. P. yesonicus adult density varied more than 10-fold among the four golf clubs where it was observed, with the most activity being at golf clubs with the most scarab adults in June and July. At Yongwon Golf Club P. yesonicus activity closely tracked Popillia quadriguttata activity and both peaked in late June and early July. The ratio of scarab adults (mostly P. quadriguttata):P. yesonicus adults was 8:1. On average mean of 7.5% of all P. yesonicus adults observed in visual surveys were holding captured prey. 50% of all captured prey was a scarab turf pest, P. quadriguttata. At Yongwon Golf Club, regression analysis indicates that P. quadriguttata activity explains 75% of the variation in activity of P. yesonicus. The potential impact of P. yesonicus on populations of P. quadriguttata and other scarab turf pests is discussed.