There are four taxa in this species group in Alberta, consisting of the Anise Swallowtail (P. zelicaon) and three subspecies of the Old World Swallowtail (P. machaon). The Anise Swallowtail occurs together with P. machaon throughout most of Alberta, and the following characters will distinguish these two species in most cases: the black pupil of the hindwing eyespot is connected to the wing margin or positioned below the red scales in P. machaon, compared to a centered, unconnected pupil in zelicaon. Occasionally, hybrid individuals displaying characters intermediate between P. m. dodi and P. zelicaon are found, while hybrids between other machaon subspecies and zelicaon can be quite common in some areas (Sperling 1987, 1990). Subspecies of P. machaon are best distinguished by location and habitat. P. m. pikei occurs in habitat similar to that of P. m. dodi, but is restricted to the Peace River grasslands. The Hudsonian Old World Swallowtail (P. m. hudsonianus) is a boreal forest species generally associated with sparsely wooded bogs. To add to the challenge in identifying members of this group, a black color form occurs rarely in populations of P. m. dodi (but not pikei or hudsonianus), in which adults have most of the yellow colouration replaced by black (Sperling 1987). This form more commonly occurs in the Anise Swallowtail (P. zelicaon) and hybrids between P. machaon and P. zelicaon. Differences in mitchondrial DNA also distinguish P. machaon from P. zelicaon (Sperling & Harrison 1994).