Visual features of the wing color, with special reference to the UV (ultraviolet) color, of the British subspecies of the cabbage butterfly, Pieris rapae rapae and its mating behavior were investigated. Both sexes of the British subspecies were found to lack UV color and differed only slightly in color in the visible color range, with female wings more yellowish. It follows that they show only slight sexual dimorphism in wing color. It was shown that the initial mate recognition was mediated visually, based on the wing color. Males discriminated between the sexes visually, but only marginally and were occasionally observed to approach other males mistakenly. The resting males approached by female-searching males displayed a flutter response, deterring the approaching males from attempting to copulate with them; i.e. it functioned as “mechanical isolation mechanism” against maladaptive copulatory attempts between males. The results are discussed in terms of the comparative ethology of the mating behavior with that of the Japanese subspecies. It is suggested that the British subspecies is ancestral to the Japanese subspecies.