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. The British race is the subspecies britannicus which is confined to the fens of the Norfolk Broads in East Norfolk. This is partly due to the distribution of the sole larval foodplant, Milk-parsley. Seeing the adult butterflies flying powerfully over the Norfolk Broads is a sight to behold, and one near the top of the list of most British butterfly-watchers.
In some years, there are reports of the gorganus subspecies arriving from the continent. This subspecies is less fussy and will use many kinds of Umbellifer, such as Wild Carrot, as the larval foodplant. 2013 was an exceptional year for this subspecies, with sightings from 13 sites across Hampshire, Sussex and Kent, and a single site in Buckinghamshire. These sightings included evidence of egg-laying and the resulting larvae and pupae have been followed through to spring 2014. On April 14th 2014 a single continental Swallowtail was seen and photographed at the Magdalen Hill Down Butterfly Conservation reserve near Winchester in Hampshire.
Papilio machaon ssp. machaon
The species was first defined in Linnaeus (1758) as shown here (type locality: Sweden). The nominate subspecies has not been recorded in the British Isles.
This subspecies was first defined in Seitz (1907) as shown here and as shown in this plate (type locality: Norfolk, England). This subspecies is indigenous to the British Isles and differs from ssp. gorganus not only in terms of its appearance but also its ecology. Specifically, ssp. britannicus is a fenland butterfly, its main foodplant is Milk-parsley (Peucedanum palustre) and it is mainly univoltine, with only a small percentage of adults going on to produce a second brood. Dennis (1977) suggests that this is genetically controlled since, according to Gardiner (1963), "A day-length of 18 hours does not prevent diapause in P. machaon".
In terms of appearance, this subspecies differs from its European counterpart, ssp. gorganus, as follows:
1. It has an overall darker appearance. The submarginal bands are particularly broad and dark in comparison.
2. Ford (1945a) states that, on the hindwing, the submarginal band, marked with blue, extends nearer to the dark mark at the end of the cell.
3. Ford (1945a) states that the ground colour is of a deeper yellow, giving ssp. gorganus a lighter appearance, although this difference is disputed by Cooke (1946).
4. Ford (1945a), Dennis (1977) and Riley (2007) state that, unlike ssp. gorganus, the submarginal bands are triangular, being wider at base of the wings and narrower at the apex, while this band is not so tapered in ssp. gorganus.
5. Riley (2007) states that ssp. britannicus is slightly smaller than ssp. gorganus.
Papilio machaon ssp. britannicus (Seitz, 1907)
Original (German)britannicus ist ein breit und tief schwarz gezeichneter machaon, mit besonders breiter, samtschwarzer Submarginalbinde; er kommt in England vor, wo machaon früher weit verbreitet war, jetzt aber auf die Sumpfdistrikte von Norfolk und Cambridgeshire beschränkt ist.Translationbritannicus is a [form of] machaon with broad, deep black markings, with particularly wide, jet black submarginal bands. It occurs in England where machaon was once widespread, but is now restricted to the fens of Norfolk and Cambridgeshire.
Photo © Julian Dowding
Papilio machaon ssp. gorganus
This subspecies was first defined in Fruhstorfer (1922) as shown here (type locality: Central Europe). This subspecies is a rare migrant from the continent. Differences between this subspecies and ssp. britannicus are given under the description of the latter. The original description in Fruhstorfer (1922) makes reference to Seitz (1907), Berge & Rebel (1910) and Spuler (1910).
Papilio machaon ssp. gorganus (Fruhstorfer, 1922)
Original (German)P. machaon gorganus nom. nov. (Gorganus , Bruder des Machaon) nicht nur bedeutend kleiner als die schwedische Nominatform bleibt, sondern auch durch kaum halb so breiten gelben Zellfleck und die um ein Drittel schmälere gelbe Region der Vorderflügel charakterisiert wird. Auf den Hinterflügeln nimmt die gelbe diskale Zone bei schwedischen machaon jenseits der Zelle einen fast 10 mm breiten Raum ein, noch ausgedehnter als sie auf der prächtigen Abbildung im SEITZ, Taf. 6c, dargestellt wird. Es ist nicht ausgeschlossen, daß Seitz einen machaon nordischer Herkunft vorgeführt hat. Eine weniger breite Gelbzone der Hinterflügel zeigt schon das Bild REBELS im BERGE, ein sehr schmales das Bild von SPULER. Ein ♀, das mit SPULERS Figur in der Enge der gelben Binde harmoniert, besitze ich aus Holland.TranslationAs a commentary on this - which is almost superfluous - it should be noted that P. machaon gorganus nom. nov. (Gorganus, brother of Machaon) is not only significantly smaller than the Swedish nominate form but also characterised by the yellow cell spot, which is barely half the width, and the yellow region of the forewing, which is up to one third narrower. On the hindwings the yellow discal zone of Swedish machaon takes up almost 10mm of the space beyond the cell, even more extensive than is shown in the magnificent illustration in SEITZ, Plate 6c. It is not impossible that Seitz has shown a machaon of northern origin. REBEL's picture, in BERGE, already shows a narrower yellow zone on the hindwing and SPULER's a very narrow one. I have a female from Holland that matches SPULER's in the narrowness of the yellow band.
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.
Papilio machaon ssp. britannicus
The chart(s) above have been correlated with the phenology plot below, taken from the UK Butterfly Monitoring Scheme. The blue line gives average counts over the full data set from 1976 to date, and the red line gives the average for the last year.
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.
The primary larval foodplant is Milk-parsley (Peucedanum palustre).
Adults feed primarily on Bluebell (Hyacinthoides non-scriptus), Devil's-bit Scabious (Succisa pratensis), Ragged Robin (Lychnis flos-cuculi), Red Clover (Trifolium pratense), Teasel (Dipsacus fullonum) and Thistles (Cirsium spp. and Carduus spp.).
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.
Papilio machaon ssp. gorganus
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.
Click here to see a full list of aberrations for this species.
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.
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.
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.
No similar species found.
Click here to see the distribution of this species overlaid with specific site information. Alternatively, select one of the sites listed below.
The status of the Swallowtail is considered to be stable, although the resident race is highly dependent on appropriate management of its fenland habitat.
|Species of Conservation Concern|
The table above shows the distribution and population trends of species regularly found in the British Isles. The distribution trend represents a comparison between data for the periods 1995-1999 and 2005-2009. The information provided is taken from the Butterfly Conservation report The State of the UK's Butterflies 2011. The UK BAP status is taken from the UK Biodiversity Action Plan (UK BAP) (2007 review).
The following links provide additional information on this butterfly.
The species description provided here references the following publications:
|Berge & Rebel (1910)|| Berge, F. and Rebel, H. (1910) Fr. Berge's Schmetterlingsbuch nach dem gegenwärtigen Stande der Lepidopterologie neu bearbeitet und herausgegeben von Professor Dr. H. Rebel.|
|Cooke (1946)|| Cooke, B.H. (1946) Papilio machaon in North West France. Entomologist's Record and Journal of Variation.|
|Dennis (1977)|| Dennis, R.L.H. (1977) The British Butterflies - Their Origin and Establishment.|
|Ford (1945a)|| Ford, E.B. (1945) Butterflies.|
|Fruhstorfer (1922)|| Fruhstorfer, H. (1922) Entomologische Rundschau.|
|Gardiner (1963)|| Gardiner, B.O.C. (1963) Notes on the Breeding and Biology of Papilio Machaon L. (Lepidoptera: Papilionidae). Proceedings of the Royal Entomological Society of London (A).|
|Latreille (1802)|| Latreille, P.A. (1802) Histoire naturelle, générale et particulière, des Crustacés et des Insectes.|
|Linnaeus (1758)|| Linnaeus, C. (1758) Systema Naturae. Edition 10.|
|Riley (2007)|| Riley, A.M. (2007) British and Irish Butterflies: The Complete Identification, Field and Site Guide to the Species, Subspecies and Forms.|
|Seitz (1907)|| Seitz, A. (1907) Gattung Papilio, Schwalbenschwanze. Die Großschmetterlinge der Erde.|
|Spuler (1910)|| Spuler, A. (1910) Die Schmetterlinge Europas.|