Both eastern tiger and pipevine swallowtails appear for the first time today, which is no surprise, since the tiger may depend partly on the pipevine. Both are certain spring heralds, but the mostly yellow tiger is more colorful than the blackish pipevine and thus more noticeable. A week ago I found fresh new tiger swallowtails on the Texas coast, and I might find the first ones in central Wisconsin in another month. This butterfly tells me that spring in eastern North America moves northward about two hundred miles per week in the warmer south but slows down north of the Mason-Dixon line.

Instead of being lemon yellow with black bars like males, early female tiger swallowtails are black with black-bar "shadows." They emerge a few days after the males but before yellow females and mimic the distasteful pipevine swallowtails for protection. Male tigers seem to prefer yellow females as mates; but black ones survive better, because predators leave them alone, so both color morphs persist in the population. In directing the play of life, natural selection puts black female tigers in the same scene with pipevines, thus gaining protective resemblance and the chance to mate with choosy males.