Despite its name, which refers to its status in England (as an extremely rare vagrant), this species is common throughout much of Europe. There is ongoing debate over whether its Iberian cousin, the Iberian scarce swallowtail, Iphiclides feisthamelii, is a subspecies or full species but more recent publications tend to count it the latter. The boundary line for the two is the Pyrenees, where I have only seen the scarce swallowtail so far, never the Iberian scarce swallowtail.

With its tiger stripes and aerodynamic elegance, this species is unlikely to be mistaken, except for Iberian scarce swallowtail at the boundary between the two. The other widespread swallowtail, Papilio machaon, has a very different appearance, with horizontal black bars following the veins, as does the much more local Corsican swallowtail, Papilio hospiton. The southern swallowtail, Papilio alexenor, found in the South of France (where it is rare) and south-eastern Europe, also lacks the transvers lines along the veins and is superficially similar, but the borders and general structure are more similar to the swallowtail than the scarce.

Distinguishing between scarce and Iberian scarce swallowtails is harder. The latter are typically a more papery white, with a distinct yellow costa to the forewing. They seem more kite-shaped for some reason. The orange and blue spot on the hindwing is subtly different too. A useful but not 100% reliable feature is the third bar out from the base on the forewing, which is typically tapered to a point, not blunt on the vein.

(scarce swallowtail on left, Iberian on right)

Scarce swallowtails may be seen as early as March in the Rhône Valley of Switzerland - perhaps even earlier further south. Their larval foodplants are various species of Prunus, around which they can often be seen, whether males looking for females or holding territories, or females looking for a place to lay. They enjoy nectaring but also come readily to mud, sometimes in numbers. They hibernate as pupae.