Black Swallowtail (Papilio polyxenes) on hostplant (Anethum sp. or Daucus sp.)
Though the exact colors and markings vary between subspecies (and even within subspecies), you can see the sexual dimorphism (phenotypic differences) between the male and the female black swallowtail here. [ETA: The female is the lower right, the male is top left]
In many butterfly species, the female is polymorphic, and can have multiple phenotypes, some even being identical to the male phenotype. What is shown here is considered the “type” (standard) for the black swallowtail species, but nearly half of the females are phenotypically different from this form. However, even when the female looks exactly the same as the male to the human eye, they maintain a distinct pattern of UV markings, that are easily visible to other butterflies.
The Natural History of the Rarer Lepidopterous Insects of Georgia, vol. 1. Sir James Edward Smith, Illustrated by John Abbot, 1797.