Steven Cheshire's British Butterflies
British Butterflies: Species: Species Account - The Swallowtail:
Swallowtail
Papilio machaon (Linnaeus, 1758)

Swallowtail egg.
ova
  Swallowtail caterpillar.
larva
  Swallowtail chrysalis
pupa
Swallowtail
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Nomenclature
Insecta: Lepidoptera : Family Papilionidae: Subfamily Papilioninae : Genus Papilio: Species machaon:
Description
The Swallowtail is one of the UK's most enigmatic butterflies and our largest buttefly. Restricted the the Norfolk Broads this unmistakable butterfly can be seen in good numbers on the broads at the right time of year. This pale yellow and black butterfly has distinctive markings which cannot be mistaken for any other species. The hindwings have a curve of electric blue spots ending in a vivid red spot. The hindwings have a distinctive tail.

The Adult butterflies generally feed on flowers during the early morning and late evening and are especially attracted to Ragged Robin and Thistles although gardens with an abundant floral display are often visited.

On dull days check patches of Ragged Robin for this butterfly. A day with a mix of sunshine and clouds is best if you intend to photograph this species as on sunny days, the Swallowtail is very active.

The Swallowtail lays its eggs singularly on the larval foodplant Milk Parsley (Peucedanum palustre). The eggs hatch in within a few weeks. The young caterpillars are black and white at first and look similar to small bird-droppings. In later instars, the caterpillars become a pale green with black and orange rings. The caterpillars of butterflies from the Swallowtail family (Papilionidae) posess a unique forked structure just behind the head which is normally hidden. Known as the osmeterium, this can be everted when the caterpillar is threatened, emiting a smelly secretion which contains terpenes. The larvae pupate within a few weeks and generally remain in this state throughout the winter, emerging as adult butterflies the following spring although, occasionally a second brood occurs in mid-summer when some pupae emerge as adults rather than emerging the following spring.

The European Race of Swallowtail (Papilio machaon gorganus) is very similar to the British Race but has a slightly paler yellow ground colour and occasionally occurs as a very rare migrant along the south coast of the UK.
Habitat
Open sedge fens and reed marshes where the larval foodplant Milk Parsley grows in abundance.
Distribution
The British Race of the Swallowtail is restricted to the Fens of the Norfolk Broads although its distribution in historical times was much greater extending into Cambrideshire.

Re-Introduction attempts at Wicken Fen:
The Swallowtail became extinct on Wicken Fen, Cambridgeshire in 1952 probably due to a variety of factors including the reduced amount of suitable open fen habitat (from 120ha to less than 8ha). Wicken Fen also became drier as the water table dropped caused by agricultural drainage... the fragments of open fen becomming unsuitable for Milk Parsley.

Several re-introduction attempts have been made at Wicken Fen as it seems unlikely that the species could colonise the site naturally. In 1974, over 2000 Milk Parsley plants were planted around Adventurers’ Fen. 228 adult butterflies bred in captivity from Hickling Broad (Norfolk) stock were released on Wicken Fen in 1975 but by 1980, the Swallowtail was again extinct on Wicken due to the loss of Milk Parsley.

During the late 1980's, early 1990's, a second attempt was made to establish a population at Wicken but several years of summer droughts meant the Swallowtail was extinct again by 1996, primarily due to the loss of the larval foodplant. No further attempts have been carried out since.
Where to see the Swallowtail in the British Isles
The British Race of the Swallowtail is restricted to the Fens of the Norfolk Broads although its distribution in historical times was much greater extending into Cambrideshire.

Key sites for the Swallowtail include:
Norfolk: Strumpshaw Fen Hickling Broad and Ranworth Broad.

Re-Introduction attempts at Wicken Fen:
The Swallowtail became extinct on Wicken Fen, Cambridgeshire in 1952 probably due to a variety of factors including the reduced amount of suitable open fen habitat (from 120ha to less than 8ha). Wicken Fen also became drier as the water table dropped caused by agricultural drainage... the fragments of open fen becomming unsuitable for Milk Parsley.

Several re-introduction attempts have been made at Wicken Fen as it seems unlikely that the species could colonise the site naturally. In 1974, over 2000 Milk Parsley plants were planted around Adventurers’ Fen. 228 adult butterflies bred in captivity from Hickling Broad (Norfolk) stock were released on Wicken Fen in 1975 but by 1980, the Swallowtail was again extinct on Wicken due to the loss of Milk Parsley.

During the late 1980's, early 1990's, a second attempt was made to establish a population at Wicken but several years of summer droughts meant the Swallowtail was extinct again by 1996, primarily due to the loss of the larval foodplant. No further attempts have been carried out since.
Other notes
The European Race of the Swallowtail which is slightly larger but colouration less intense occurs on rare occations on the south coast of the UK.
Lifecycle chart
pupapupapupapupaadultovaovalarvaepupaadultlarvaepupaadultovalarvaepupaadultpupapupapupa
 
Flight chart
JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecember
The lifecycle and flight charts should be regarded as approximate guides to the Swallowtail in Britain. Specific lifecycle states, adult emergence and peak flight times vary from year to year due to variations in weather conditions.
IUCN category status 2010 5   IUCN category status 2007 34
--awaiting data-- --awaiting data--

5Fox, R., Warren, M., Brereton, T. M., Roy, D. B. & Robinson, A.
(2010) A new Red List of British Butterflies. Insect Conservation and Diversity.
Near Threatened Near Threatened

3Fox, R., Warren, M & Brereton, T.
(2007) New Red List of British Butterflies. Butterfly Conservation, Wareham.

4More information about IUCN categories.
Wingspan
76-93mm
UK status
Resident
Larval foodplants
Milk Parsley (Peucedanum palustre) is the sole larval foodplant in the UK.
British subspecies
Papilio machaon ssp. britannicus (Seitz, 1907)
Restricted to the Norfolk Broads.
Butterflies of Britain ID Chart
Your personal guide to British Butterflies. This 8-panel laminated chart is designed for speedy butterfly identification in the field. Ideal for anyone interested in identifying butterflies, perfect for children and adults and ideal for outdoor use, laminated, shower-proof and robust. Get your copy today.
Butterflies of Britain (Laminated ID Chart).
Online store
Visit our online store for many more butterfly related books and gifts.
Population trends 1
UK Population trend 1995-2004 insuficient data
UK Population trend 1976-2004 insuficient data

1Fox, R., Asher. J., Brereton. T., Roy, D & Warren, M. (2006) The State of Butterflies in Britain & Ireland, Pices, Oxford.
UK BAP status 2
UK BAP status species of conservation concern (link)

2For information about the UK Biodiversity Action Plan, visit the JNCC web site jncc.defra.gov.uk.

National Biodiversity Network Gateway
National Biodiversity Network Gateway Distribution Map



Areas in and indicate a contraction in distribution of the Swallowtail except in Ireland where data is only available up until 1999.

* Records shown in outside the natural distribution may be the result of illegal or accidental releases by breeders or, depending upon the species, migrant individuals from mainland Europe.

Key to map*
= 2000 to 2010 inclusive (current distribution)
= records from 1950 to 1999 inclusive
= records from 1900 to 1949 inclusive
Records prior to 1st January 1900 are not shown.

The NBN Gateway records are shown on the map right. (See terms and conditions).

More data is available on the Swallowtail on the NBN Gateway web site.
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References
For full details of books and reports mentioned on this web site, view the references page.

Find out more online*
Swallowtail can be found on Peter Eeles excellent UK Butterflies web site.
Swallowtail can be found on Matt Rowlings excellent European Butterflies web site.

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Photographs of the Swallowtail
There are 0 photographs of the Swallowtail in our stock photo library.
Aberrations and forms
There are 9 named aberrant forms of the Swallowtail currently listed. Find out more about aberrants here.

ab. conjuncta - Rocci 1919
ab. evittata - Spengel 1899
ab. hiemalis - Fettig 1910
ab. latelutea - Goodson 1959
ab. niger - Heyne 1895
ab. obscura - Frohawk 1938
ab. punctatoclavatus - Cabeau 1911
ab. rufa - Pionneau 1924
ab. tenuivittata - Spengel 1899