The Swallowtail butterfly, also called the Common/Yellow Swallowtail, particularly outside of the UK where there may be other swallowtail species, is the UK's largest resident butterfly (the Monarch is the largest - rare - migrant). The British subspecies, P.
m. britannicus, (of 37 subspecies in total) is prevalent only in the Norfolk Fens area.
On the south coast the slightly larger and paler Continental migrant species P.
m. gorganus (illustrated) may rarely be seen.