Beak marks on butterfly wings have been used as an indicator of predation pressure. The relationship between butterflies and their predators in the field was examined to evaluate the beak mark rate as an indicator of predation pressure. Transect censuses were conducted to measure the beak mark rate on butterflies from May to November, 2010, in Shiga Prefecture, Japan. A total of 1216 butterflies of 42 species from five families were observed during the study period. The beak mark rate in the Papilionidae was significantly higher than those of all other families. Analysis of the monthly fluctuations in the beak mark rate and relative abundance of predators revealed that the higher beak mark rates observed for two butterfly families (Papilionidae and Nymphalidae) were significantly and positively related to predation pressure, while no significant relationship was found for other families (Lycaenidae, Pieridae and Hesperiidae). Beak marks in larger butterflies (Papilionidae and Nymphalidae) can be used as an indicator to evaluate the relative intensity of predation pressure in the field.