Perseverance did eventually pay off and I finally have been rewarded for all of those times I ran back into the house to get my camera, only to have my flighty friend disappear before I could frame the shot.
The Swallowtail, named after the appearance of it's tail to the tail of some swallows, is not a rarity to Portugal - Swallowtails exist on all continents except Antarctica.
I now look forward to an autumn Swallowtail rush to my lantana, and the possibility of taking a family portrait snap.
Edited 21 September: More photos available here.