Swallowtail (Papilio machaon)

Also known as: Common swallowtail
GenusPapilio (1)
SizeWingspan: 6.4 – 7.6 cm (2)
Caterpillar length: up to 4.1 cm (3)

Listed as a species of conservation concern by the UK Biodiversity Action Plan and fully protected in Great Britain (4).

The swallowtail is perhaps one of our rarest and most beautiful butterflies. The endemic race that occurs in Britain (Papilio machaon britannicus) is found only in the Norfolk Broads (4). It is yellow in colour with stunning black markings with a red spot on the hind wings capped with blue. The underside is somewhat paler in colour (2). Initially the young caterpillars resemble a bird dropping, which protects them from being eaten by potential predators. After a couple of moults, the plump, large caterpillar will have developed a bright green body with black bands along the body and yellowish-orange spots (3).

The British race (britannicus) is found only in the Norfolk Broads, and once had a much wider range, extending throughout the East Anglian Fens, the Somerset Levels, the marshes along the Thames, reaching as far north as Yorkshire (4). These wetland areas have long since been drained. The species was lost from Wicken Fen in Cambridgeshire in the 1950s and attempts at reintroduction have been made, so far with little success (4). The European race (gorganus) has a wide distribution in Europe, extending through Asia to Japan and also occurs in North America (4).

Breeds only in fens and marshes (3).

The swallowtail produces a single brood a year in the Norfolk Broads, but a second brood may be produced in some years (4). The sole foodplant is milk parsley (Peucedanum palustre) (3). Adults are on the wing from late May to mid July, and second brood adults are present in August (4). Females lay their eggs singly on the leaves of milk parsley and the caterpillars hatch out after around one week. They are active during the day and feed on the foodplant for about a month until they are fully grown. If disturbed, a pair of bright orange scent glands emerge from just behind the head; these horn-like structures repel potential predators by the strong unpleasant smell that they emit (3). The caterpillars attach their pupae low down on plant stems; the adults emerge either within three weeks, or after hibernating through the winter (3).

The habitat of this species has undergone a serious and sustained decline, with a shocking 1% of the original extent remaining today (4). The Fenland remaining on the Norfolk Broads is at great risk from falling water tables, pollution and the growth of scrub. The remaining habitat is significantly fragmented (4).

The swallowtail population reached a low in the 1970s, but conservation action has since helped numbers to increase. The entire Broads area has been designated as an Environmentally Sensitive Area (ESA) whish enable grants to land owners to encourage environmentally friendly land-management. Provided that current management measures continue, the future for the swallowtail at the Norfolk Broads looks fairly promising (4).

For more on butterflies, their conservation and details of how to get involved see: Butterfly Conservation:

For more on butterflies see: The Millennium Atlas of Butterflies in Britain and Ireland by: Asher, J., Warren, F., Fox, R. Harding, P., Jeffcoate, G. & Jeffcoate, S. Published by Oxford University Press.

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. National Biodiversity Network Species Dictionary (January2004):
  2. Still, J. (1996) Collins Wild Guide Butterflies and Moths of Britain and Europe. HarperCollins Publishers, London.
  3. Carter, D. & Hargreaves, B. (1986) A field guide to caterpillars of butterflies and moths in Britain and Europe. William Collins & Sons Ltd, London.
  4. Asher, J., Warren, F., Fox, R. Harding, P., Jeffcoate, G. & Jeffcoate, S. (2001) The Millennium Atlas of Butterflies in Britain and Ireland. Oxford University Press, Oxford.