Cytochrome P450s are a superfamily of enzymes thought to have derived from an ancestral gene due to duplication and diversification. They are grouped into different hierarchies based on overall amino acid (AA) sequence identity. AA sequences of high identity are often arbitrarily assigned as variants of the same gene due to the lack of genome-wide sequence information. This arbitrary assignment does not address the question as to whether these variants are polymorphic alleles at the same locus or diversified duplicates at different loci. CYP6B1 is the major enzyme responsible for the exclusive feeding of black swallowtail, Papilio polyxenes on plants containing toxic furanocoumarins; three variants for CYP6B1 (v1, v2 and v3) have been reported. We analyzed individual swallowtail caterpillars from different lineages in terms of their CYP6B1 genotype identity and metabolic activity.