Swallowtail (Papilio machaon) Image by Pixabay
The swallowtail butterfly is attractively marked in yellow and black and is one of the rarest butterflies in the UK being confined to the fenland in the Norfolk Broads area. This is because in Britain its caterpillar will only feed on the milk parsley (Peucedanum palustre).
The swallowtail takes its name from projections on its hind-wings which also have some blue colouration on them and a bright red spot.
Caterpillars of continental swallowtails will eat a wide variety of food-plants including species in the Apiacae (parsley family) such as wild carrot (Daucus carota) and fennel (Foeniculum vulgare), as well as the rue (Ruta graveolens).
Swallowtail caterpillars are easy to spot because they have bold blackish stripes on their green bodies. They also have a weird forked organ known as an osmeterium that is protruded if the insect larva is threatened. This organ emits an unpleasant smell that is thought to help ward off predators.
Swallowtail caterpillar on rue. Photo by Steve Andrews
Swallowtails are fairly common and widely distributed in many parts of Europe and in Portugal, for example, they can be seen in gardens where the eggs get laid on rue.
Swallowtails sometimes migrate from France to the UK and there have been reports of them breeding but the only native species are to be found in the Norfolk Broads as already noted.
There are many other types of swallowtail butterfly found around the world. Some of these are common but others are endangered butterfly species.
The swallowtail butterfly is a very beautiful insect and it would be a very great shame if the British type ever becomes extinct.