No.043 · Butterflies, moths and other insects · Rare

Swallowtail

Papilio machaon britannicus

Britain's largest butterfly, yellow and black with blue and red spots on its hindwings. This subspecies lives only in the Norfolk Broads.

When to look

June to July, mostly at day.

Best time: Sunny days. Main flight May–July, best around mid-June; occasionally a second brood from late August to mid-September.
Where in the game: the Norfolk Broads (fen, reedbed and grazing marsh)
Size: Wingspan males 76–83 mm, females 86–93 mm (Butterfly Conservation)
Wingspan: 76–93 mm
Population: Restricted to the Norfolk Broads (Butterfly Conservation)
Status: Vulnerable (GB Red List, 2022)

Caterpillars eat milk-parsley only; adults take nectar from thistles and ragged-robin

Open fen with milk-parsley and wet flowery meadows

Eggs are laid on milk-parsley; usually one generation a year, occasionally a second in late summer.

The British race, Papilio machaon britannicus, is found nowhere else in the world (Norfolk Wildlife Trust).
Continental migrants sometimes turn up, but they use other plants such as wild carrot.
It is Britain's largest butterfly (Norfolk Wildlife Trust), and the native caterpillars feed only on milk-parsley (Butterfly Conservation).

Egg-laying June, day
A female skims low over the fen, dabbing eggs on milk-parsley leaves.
Nectaring May to July, day
A swallowtail quivers its wings while sipping nectar from a thistle.

Photograph in cool early morning or cloudy spells when it is still; a macro lens and gentle approach let you fill the frame.

Fully protected: never catch, handle or collect. Stay on paths so you do not trample milk-parsley.

Fully protected in Great Britain under Schedule 5 of the Wildlife and Countryside Act 1981 (legislation.gov.uk).