A reader sent in a question asking me to explain this: a swallowtail wings with different color patterns. Has anybody seen anything like this before? Got any explanations?
My first thought was that it was a genetic mosaic. A mitotic error in early development can lead to one wing primordium carrying a mutant allele, and the other carrying a wild-type form. At metamorphosis, the differences would become visible. It could be a defect that knocks out one pigment on pale wing, or since swallowtails can show sexual and seasonal dimorphism, it could be a change that switches on or off a male/female pattern, or an early summer/late summer pattern. Alternatively (and probably less likely), since seasonal morphs are switched by environmental conditions, this could have been a pupa in a very odd place that got different signals on the two sides.
If you’ve got a better idea, pass it on in the comments.