Jenny sent these photos to me some time ago. Taken in July 2006, they show yet another visitor to her backyard garden. You might remember the black swallowtail butterfly (Papilio polyxenes) seen here and here. Suffice it to say Jenny has gone to great lengths to make her garden attractive to butterflies, and this represents yet another example of her success in that regard.
What you see below is called an intergrade species. Essentially, it’s a hybrid between the red-spotted purple (Limenitis arthemis astyanax) and white admiral (Limenitis arthemis arthemis or Limenitis arthemis rubrofasciata) butterflies. The species designation is simply Limenitis arthemis to show it is not one of the specific subspecies.
Thanks to Abe’s comment, I now know this is the black form female Eastern Tiger Swallowtail (Papilio glaucus). After looking at photos of this species along with several others, it made my head hurt because they all look so much alike. Thankfully there are those who know a great deal more about them than I do and can offer informed direction—which I greatly appreciate.