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 see a swallowtail
June to July, mostly by day.
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Time of day
- Dawn
- Day
- Dusk
- Night
Where to see a swallowtail in the UK
- The Norfolk Broads. Hickling Broad and Marshes, Ranworth Broad and RSPB Strumpshaw Fen; flies over fen with milk-parsley.
Swallowtail facts at a glance
- 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)
Diet
Caterpillars eat milk-parsley only; adults take nectar from thistles and ragged-robin
Habitat
Open fen with milk-parsley and wet flowery meadows
Breeding
Eggs are laid on milk-parsley; usually one generation a year, occasionally a second in late summer.
Field signs
- Large yellow-and-black butterfly gliding slowly over reeds
- Green caterpillar with black bands and orange spots on milk-parsley
- Tailed hindwings with a red eyespot
Did you know?
- 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).
Moments worth waiting for
- Egg-laying
A female skims low over the fen, dabbing eggs on milk-parsley leaves. - Nectaring
A swallowtail quivers its wings while sipping nectar from a thistle.
Photo tip
Photograph in cool early morning or cloudy spells when it is still; a macro lens and gentle approach let you fill the frame.
Be a good naturalist
Fully protected: never catch, handle or collect. Stay on paths so you do not trample milk-parsley.
The law
Fully protected in Great Britain under Schedule 5 of the Wildlife and Countryside Act 1981 (legislation.gov.uk).
