The tie you might ask? They're considered the same species (Limenitis arthemis). Yep. They look completely different but you have to delve deep into their teeny-tiny mitochondrial DNA to find any genetic variation.
Because they do hybridize, there are considered a polytypic species with two subspecies: the Red-spotted Purple (Limenitis arthemis astyanax), found throughout most of the United States (I love the reddish tips on the antennae!):
and the White Admiral (Limenitis arthemis arthemis), found in the northern United States and Canada:
Some references list a third form, the Western White Admiral, found west of the Rockies, that looks the same as the White Admiral, but with the addition of red spots on the hindwings. My purely unscientific mind says to listen to the various scientific sources and stick with two distinct subspecies with hybrids occurring between the two. Dan Tallman's blog has a nice photo of such an intergrade.
Of interest, the Red-spotted Purple is a Batesian mimic of the Black Pipevine Swallowtail. It has developed color mimicry to help deter predators (the Black Pipevine Swallowtail is poisonous and birds have learned to avoid it, and anything resembling it).
So cool to see these two back-to-back!
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