How does the black wing tip marking extension differentiate Large White from Small White?
Large White has extensive marks continuing a significant distance along the outer edge, while Small White's are less-extensive, extending slightly.
When the underside observation leads to distinguishing between the Large White (P. brassicae) and the Small White (P. rapae) because both exhibit a plain underside, the observer must rely on the extent of the apical marking visible on the upper wing tips. The Large White features extensive black marks at the wing tips, where the dark color travels a significant distance along the outer edge of the wing. In sharp contrast, the Small White displays less-extensive grey or black markings at the tips, with the coloration extending only slightly down that outer edge. This subtle difference in the longitudinal spread of the apical marking is a crucial physical differentiator between the two otherwise similar species.
