UK Butterflies - Swallowtail

Wingspan
Male: 76 - 83mm
Female: 86 - 93mm

Swallowtail

Papilio machaon

pa-PILL-ee-oh
ma-KAY-on

Linnaeus, 1758

Ref: 1539

Superfamily:	Papilionoidea
Family:	Papilionidae
Subfamily:	Papilioninae
Genus:	Papilio
Subgenus:
Species:	machaon
Subspecies:	britannicus (Seitz, 1907)
	gorganus (Fruhstorfer, 1922)

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Introduction
Distribution
Annual Cycle
Habitat
Larval Foodplants
Nectar Sources

Imago
Ovum
Larva
Pupa
Similar Species
Videos

Sites
Conservation Status
Links
References

Male

Swallowtail - imago - Strumpshaw Fen - 12-Jun-06 (0296)

Male Underside

Swallowtail - imago - Thatcham - 20-May-08 (7) {REARED}

Female

Swallowtail - imago - Hickling Broad - Unknown date [Julian Dowding]

Female Underside

	Introduction

The Swallowtail is our largest native butterfly, and also one of our rarest. This spectacular insect is our only resident butterfly of the Papilionidae family, which is one of the largest butterfly families in the world. Seeing the adult butterflies flying powerfully over the fens is a sight to behold, and one near the top of the list of most British butterfly-watchers. The British race is the subspecies britannicus although, in some years, there are reports of the gorganus subspecies arriving from the continent. The British race is slightly smaller and darker than its continental cousin.

Subspecies: britannicus

This subspecies is indigenous to the British Isles, and is darker than its European counterpart, which is the subspecies gorganus.

Subspecies: gorganus

This subspecies is a rare migrant from the continent.

	Distribution

The British subspecies is confined to the fens of the Norfolk broads. This is partly due to the distribution of the sole larval foodplant, Milk-parsley. The continental subspecies is less fussy and will feed on many kinds of Umbellifer, such as Wild Carrot.

	Annual Cycle

The butterfly is on the wing from late May until early July. There is usually a single generation each year although, in some years, there is a small 2nd generation.

Subspecies: britannicus

	Habitat

The britannicus subspecies inhabits open fens where the larval foodplant, Milk-parsley, is found. Such fens are usually dominated by sedge or reed. The gorganus subspecies is a migrant and can be found almost anywhere, but most frequently on open grassland near the south coast of England.

	Larval Foodplants

The primary larval foodplant is Milk-parsley (Peucedanum palustre).

	Nectar Sources

Adults feed primarily on Bluebell (Hyacinthoides non-scriptus), Devil's-bit Scabious (Succisa pratensis), Ragged Robin (Lychnis flos-cuculi), Red Clover (Trifolium patense), Teasel (Dipsacus fullonum) and Thistles (Cirsium spp. and Carduus spp.).

	Imago

This butterfly is often seen flying strongly over the fens. Even when feeding, the butterfly will typically continue to beat its wings as it takes nectar. Females generally mate on the day of their emergence, normally in the morning, and the pair remains coupled for several hours. When egg-laying, the female will fly low over vegetation looking for suitable plants on which to lay. Both sexes rely on nectar, and have a preference for pink or mauve flowers, such as Ragged Robin and Thistle.

Subspecies: britannicus

Swallowtail ssp britannicus Strumpshaw Fen RSPB, 24th May 2008

Photo © NickB

Swallowtail - imago - Strumpshaw Fen - 07-Jun-05 (7)

Photo © Pete Eeles
07-Jun-2005

Photo © Pete Eeles
12-Jun-2006

Photo © Pete Eeles
03-Jun-2007

Swallowtail - imago - Thatcham - 18-Jun-07 (1) {REARED}

Photo © Pete Eeles
18-Jun-2007

Swallowtail - imago - Thatcham - 20-May-08 (4) {REARED}

Photo © Pete Eeles
20-May-2008

Photo © Julian Dowding

Photo © Nick Sampford

Photo © Nick Sampford

Photo © Nick Sampford

Subspecies: gorganus

Swallowtail (ssp gorganus) female - Kos - 10-July-08

Photo © Denise

Swallowtail - imago - Thatcham - 11-Jun-05 (0726) [REARED]

Photo © Pete Eeles
01-Jun-2005

Swallowtail - imago - Thatcham - 11-Jun-05 (0730) [REARED]

Photo © Pete Eeles
11-Jun-2005

Swallowtail - imago - Hungary - 08-Jul-05 (0737)

Photo © Pete Eeles
10-Jul-2006

Swallowtail - imago - Sarnano, Italy - 21-Jun-08 (1)

Photo © Pete Eeles
21-Jun-2008

	Aberrations

Aberration in this magnificent species is scarce, but when it does occur it is usually spectacular.

Due to the scarcity of aberrations in this species together with the high prices that such specimens commanded at natural history auctions, this species has been subject to some fraud historically, with artificially coloured specimens being sold as the extreme ab. niger (described below).

Specimens in old collections sometimes exhibit ground colour of orange or dark yellow however these should be treated with caution: killing agents such as ammonia and hydrogen cyanide were commonly used in the early 20th century and it is now known that such chemicals can alter the colour of some species over time.

There are 94 named aberrations known to occur in Britain; a selection are described below.

ab. atrofasciata (Rocci)

On the hindwings there is little blue on the marginal band and what remains is of a pale shade, invisible in certain lights.

ab. burdigalensis (Trimoulet)

Ground colour dark yellow or orange-yellow. Most extant specimens of this aberration are thought to be as a result of exposure to chemical action as described above, however, the true form does exist in bred specimens.

ab. clara (Rocci)

Great reduction of the black bands and black spots together with an almost total absence of the black veining on all wings and the black dusting of scales at the base of the wings.

ab. eminens (Schultz)

On the forewings the marginal band is dusted with brilliant blue scales. On the hindwing the band is blue without black scaling.

ab. flava (Tutt)

Ground colour pale primrose yellow.

ab. niger (Heyne)

The wings all black and the normal black markings just faintly discernable.

ab. tristis (Stattermayer)

On the hindwings the marginal band is dusted with yellow instead of the normal blue scales.

	Ovum

Eggs are laid singly on tall flowering Milk-parsley plants. The spherical egg is yellow when first laid, but darkens as the larva inside it develops. The female tends to select exposed plants, rather than those growing among vegetation. Eggs hatch in just over a week.

Swallowtail - ovum - Norfolk - 12-Jun-05 [Trevor Sawyer]

Photo © Trevor Sawyer

Swallowtail - ovum - Unknown location - Unknown date (2) [REARED] [Brian Clegg]

Photo © Brian Clegg

	Larva

The larva eats some of the eggshell on hatching, and its appearance changes as it grows; it closely resembles a bird dropping in the early instars but, after the 3rd moult, displays much brighter warning colouration. The larva has a curious bright-orange organ called an “osmeterium” that is situated behind the first segment. This organ is used as a defence mechanism, and is protruded when the larva is threatened, giving off a pungent smell similar to rotting pineapple. This stage lasts approximately 4 weeks.

Swallowtail - larva - Thatcham - 06-Jun-05 [REARED]

Photo © Pete Eeles
06-Jun-2005

Swallowtail - larva - Thatcham - 07-Sep-06 (0762) [REARED]

Photo © Pete Eeles
07-Sep-2006

Swallowtail - larva - Thatcham - 10-Sep-06 (0771) [REARED]

Swallowtail - larva - Thatcham - 19-Jun-05 [REARED]

Swallowtail - larva - Thatcham - 20-Aug-06 (0704) [REARED]

Swallowtail - larva - Thatcham - 23-Aug-09 (1) {REARED}

Swallowtail - larva - Norfolk - 02-Aug-05 (2) [Trevor Sawyer]

Swallowtail - larva - Norfolk - 02-Aug-05 (3) [Trevor Sawyer]

	Pupa

The fully-grown larva leaves its foodplant to pupate low down on any reed or woody stem within 10m from the foodplant. The pupa is attached upright to a plant stem by a silk girdle and the cremaster, and overwinters. Two main colour forms of the pupa exist, to blend into the surroundings as appropriate. One form is greenish-yellow, the other is brown with black markings.

Swallowtail - pupa - Thatcham - 04-Oct-04 (2) [REARED]

Swallowtail - pupa - Thatcham - 05-Jul-05 [REARED]

Swallowtail - pupa - Thatcham - 06-Jun-05 [REARED]

Swallowtail - pupa - Thatcham - 13-Mar-07 (1) {REARED}

	Similar Species

No similar species found.

	Videos

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	Sites

Click here to see the distribution of this species overlaid with specific site information. Alternatively, select one of the sites listed below.

Rating	Sites
	Hickling Broad, How Hill
	Catfield Fen, Ranworth Broad, Wheatfen Broad



Not rated	Strumpshaw Fen

	Conservation Status

The status of the Swallowtail is considered to be stable, although the resident race is highly dependent on appropriate management of its fenland habitat.

UK BAP Status	Distribution Trend	Population Trend
Species of Conservation Concern		Insufficient Data

From The State of Butterflies in Britain and Ireland and the UK Biodiversity Action Plan (UK BAP) (2007 review).

	Links

The following links provide additional information on this butterfly.

	References

The species description provided here has been derived from the author's own observations and the information contained in the following works:

A Natural History of British Butterflies, by F.W.Frohawk.
British and Irish Butterflies, by Adrian M. Riley
South's British Butterflies, by T.G.Howarth (which is based extensively on the classic work, "The Butterflies of the British Isles", by Richard South).
The Butterflies of Britain and Ireland, by Jeremy Thomas and Richard Lewington.
The Millennium Atlas of Butterflies in Britain and Ireland, by Jim Asher, Martin Warren, Richard Fox, Paul Harding, Gail Jeffcoate, Stephen Jeffcoate.
The Moths and Butterflies of Great Britain and Ireland Volume 7 (1) Hesperiidae to Nymphalidae (the Butterflies), by A. Maitland Emmet and John Heath (editors).
The State of Butterflies in Britain and Ireland, Richard Fox, Jim Asher, Tom Brereton, David Roy and Martin Warren.