The Scarce Swallowtail is a large butterfly; its wingspan ranges between 6.5 and 8.0 cm. Its black tiger stripes are on a wing background that varies from fairly bright yellow in the first brood to almost pure white in second brood butterflies. The undersides of the wings are coloured very similarly to the uppersides but with less black colouring near the wing margins. There is no distinctive difference in patterning between males and females.
Other than as a vagrant flying across from central and southern Europe, this large and majestic butterfly is absent from Britain. Its common name reflects the rarity of it being seen in Britain, where early lepidopterists named it. Certainly in France and many other parts of mainland Europe it is a more common sight than the Swallowtail, Papilio machaon, which is sometimes referred to as the Common Swallowtail.
With climate change this once rare visitor to Britain may eventually be seen rather more often, but at present it is still unusual to see a Scarce Swallowtail anywhere except for the occasional migrant in the south-east of England. Scarce Swallowtails are a very common sight on mainland Europe and the Far East.
The larval foodplants are various Prunus species including Almond, Cherry, Blackthorn and Hawthorn, on the leaves of which the near-spherical eggs, initially green, are laid. The eggs change colour as the embryonic larvae develop inside them.
In the northern half of its range the Scarce Swallowtail produces just one brood between May and July, while further south there are two or even three broods between May and August; the Scarce Swallowtail can be seen on the wing until late September or early October, depending on location.
Dark brown when very young, the caterpillars soon turn bright green and develop fine yellowish dorsal and side stripes. The larvae usually develop an osmeterium, a retractable fleshy organ on the first segment of the thorax that serves as a defence mechanism by giving off an unpleasant odour.
This butterfly species overwinters in its pupal stage inside a buff-brown chrysalis; however, where an earlier summer brood occurs the chrysalises are green (and hence well camouflaged against a background of foliage).
This page includes pictures kindly contributed by Steve Jelf.
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