Last summer I made a number of visits to the Hotel Semáforo de Bares, an attractive location in NW Spain, with panoramic views over the sea and Cape Bares (Cabo de Bares) in Galicia. The hotel and grounds are located on the top of a granite hill (210m above sea level), with surrounding areas of thick gorse, grass and woodlands (see below).

On all four occasions, from mid June to late September in 2017, I came across Common Swallowtail butterflies (Papilio machaon) at the same location – the highest point – on the edge of the hotel gardens. The butterflies appeared to have territories which overlapped both the hotel gardens – with plenty of nectar laden flowers – and the contiguous, untamed rocky grass/gorse-land (see below).

Male swallowtails are well-known for visiting hill-tops – a phenomenon called hill-topping – where they establish territories as location sites for meeting females. I guess it is then a matter of waiting for virgin females to make their way up the mountain looking for mates! The males perch on prominent sites, such as rocks or stems of grass (below). They emit strong scents, which it is said can be smelt by humans (5), so the females might be able to find them this way, although it is unlikely that this occurs over long distances.

Papilio machaon has a huge Palaearctic distribution (Eurasia north of the Himalayas, together with North Africa and the temperate part of the Arabian peninsula) with a large number (at least 37 according to Wikipedia) of subspecies. Most European field guides make little or no mention of these subspecies although some, like the Maltese race (Papilio machaon melitensis) and the British race (P. m. britannicus) are well-known and well-defined.

Interestingly, the swallowtail which occurs in Corsica and Sardinia, the Corsican swallowtail (Papilio hospiton) is a separate and ‘ ‘good’ – a word used by taxonomists to imply that there is a consensus of agreement – species according to Clarke, S. C., & Larsen, T. B. (1986), although it does hybridise with Papilio machaon swallowtails who manage to fly across the Mediterranean to Sardinia and Corsica (1).

European subspecies

There clearly are readily observable morphological differences between some of the Swallowtail subspecies, including the British race (Papilio machaon britannicus), which now only occurs in the Broadland area of Norfolk, UK. Shown here. I have not (yet!) seen our indigenous British subspecies  but it is said to differ from the Continental race (ssp. gorganus) in terms of both its appearance and ecology. Differences between ssp. gorganus and ssp. britannicus are described on the UK Butterflies site. Ecologically, the two species are also very distinct, with ssp. gorganus being larger and more robust. Papilio m. gorganus is an active migrant, found in a wide range of habitats (3), whilst  P. m. britannicus is more sedentary and restricted to a single larval food-plant: milk parsley (Peucedanum palustre). 

The Continental race, P. m. gorganus, occasionally migrates across the Channel, and in 2013 Continental swallowtails were reported in a number of southern counties, including Dorset. Individuals were  rather worn, as befits a long-distance traveler! Reportedly, they bred and overwintering in southern England, appearing the following summer. In 2014, there were again further sightings of in Sussex, according to the Butterfly Conservation site, and reported in the Guardian on 11 June 2014. Perhaps this race will eventually colonise the British Isles, if the climate continues to warm. How nice would that be!

The Continental race (i.e. P. m. gorganus) is usually described as being widespread on mainland Europe (including southern Europe) but I am not aware of any publication which accurately describes the distribution of this subspecies (I am using the word ‘race’ as synonymous with subspecies in this case). The continental subspecies has a much narrower band of black near the outer margin of the fore-wing than the UK subspecies. A photograph of a continental swallowtail, seen on the top of a high mountain ( Mt. Ventoux, 1911 m a.s.l.) in the south of France, is shown here. A nice video of a Swallowtail hill-topping in Malta is shown here. They look very similar to the ones I am showing here.

The Swallowtails which occur on the Iberian Peninsula (Portugal and Spain) are often referred to as Papilio machaon hispanicus. There are plenty of listings and sightings from Spain and Portugal using this particular subspecies name, i.e. hispanicus, and it is listed in Fauna Iberica as such. Here is a specimen photographed in Sabón, Province of Galicia, in NW Spain. This race/subspecies is however, omitted from many lists of subspecies for Papilio machaon, including Butterflycorner and Wikipedia. There is an interesting online discussion on whether there are genuine differences between P. m. hispanicus and P. m. gorganus which suggests that there are, based on the fact that P. m. hispanicus hybridises with a North African subspecies (P. m. mauretanica). I think the last word on this matter should however, go to the eminent lepidopterists, Sir Cyril Clarke and Torben Larsen:

 “We therefore suggest that the entire P. machaon complex is in a labile state as regards speciation throughout its range and the relationships between the various forms are not easily expressed through the traditional species and subspecies concepts.” (2)

This quotation suggests that the variation within Papilio machaon is rather fluid and changeable (labile). It seems to me that the subject – variation within Europe and Asia – is ripe for a definitive academic study. The North American subspecies appear to be better defined and deliniated than our European ones (6), but I may be unaware of some key literature. In deference to my Spanish friends however, I will call these butterflies Papilio machaon hispanicus.

Generational changes at the Bares site in Galicia

23 June 2017

It is difficult to say for certain, but this individual looks like it might be a first generation butterfly. First generation adults – that emerge from overwintering pupae – are usually smaller and darker and the blue spots in the black post-discal band are rather obscure (4), as in this case (below). On the other hand, there is already a fair dusting of pale yellow scales on the black areas of the upper fore-wings, but not nearly so much as individuals that seen later in the year (below). The abdomen is also black, which is a good indication of a first generation butterfly (compare with the yellow abdomen with black dorsal stripe on later butterflies, shown below). Note how the orange (rather than red) anal spots are somewhat concealed. There is however, evidence of beak marks, so this butterfly has already survived one or more predation attempts.

15 August 2017

It is immediately clear that the individual photographed on the 15th August (below), is more heavily dusted with pale yellow scales, and the blue markings are slightly better defined. The orange anal spots are once again pecked out, illustrating how useful they are in terms of deflecting presumed attacks by birds.

14 Sept 2017

When I returned, about a month later in mid-September, I came across some new individuals. It is easy to distinguish between individuals when the are adorned with beak marks (i.e. where birds have had a peck at them). Unlike the individuals seen on previous visits, this handsome butterfly had intact anal spots, and just a single beak mark on the hind margin of the left hind-wing (below). The yellow dusting appears to have increased, especially on the post-discal black bands on the fore-wings. The black dorsal stripe on the yellow abdomen appears to be slightly narrower. It is as though these features – a yellowing essentially – have increased again, suggesting a possibly third generation. These changes cleverly match the general yellowing of herbage as the season progresses, although they are not exactly trying to hide! I have seen reports of four generations of this butterfly in southern Spain, but in this much cooler region of NW Spain, three generations would seem to be the maximum.

My final visit to the site, came two weeks later on 28 September. The swallowtail butterflies I came across then were all very worn, and were in a different location. They were busy nectaring on Viper’s bugloss flowers slightly lower down from the hill-topping site. They were definitely the last of the season. Perhaps they were females? The sexes are similar, so I don’t think it is possible to tell them apart from photographs.

So, we have seen from this dip into Swallowtail (Papilio machaon) biology that they are an interesting species which have formed some well-defined subspecies (like the British race), whilst in other locations the differences seem more fluid and changeable. They have the remarkable ability to change in appearance, from generation to generation, throughout the summer. Some are long-distance migrants which probably have the ability to hybridise with local races. Hybrid populations have been identified in North America (6) and perhaps some exist in Europe. Whether these races are genuine subspecies is probably best left to taxonomists – not that there are many of those these days! – using modern methods. Nevertheless, it is interesting for us naturalists to compare and contrast swallowtail butterflies from different regions of Europe to see whether we can detect differences which are apparent in the field. There is still scope for plenty of old-fashioned observation and virtual collection by photographs.

For interest, I wrote a previous blog on puffballs found at this site!

References

1. Cianchi, R., Ungaro, A., Marini, M., & Bullini, L. (2003). Differential patterns of hybridization and introgression between the swallowtails Papilio machaon and P. hospiton from Sardinia and Corsica islands (Lepidoptera, Papilionidae). Molecular Ecology, 12(6), 1461-1471.
2. Clarke, S. C., & Larsen, T. B. (1986). Speciation problems in the Papilio machaon group of butterflies (Lepidoptera: Papilionidae). Systematic entomology, 11(2), 175-181.
3. Dempster, J. P. (1995). The ecology and conservation of Papilio machaon in Britain. In Ecology and conservation of butterflies (pp. 137-149). Springer, Dordrecht.
4. Higgins, L. G., & Riley, N. D. (1970). A field guide to the butterflies of Britain and Europe. A field guide to the butterflies of Britain and Europe.
5. Ômura, H., Honda, K., & Hayashi, N. (2001). Identification of odoriferous compounds from adults of a swallowtail butterfly, Papilio machaon (Lepidoptera: Papilionidae). Zeitschrift für Naturforschung C, 56(11-12), 1126-1134.
6. Dupuis, J. R., & Sperling, F. A. (2015). Repeated reticulate evolution in North American Papilio machaon group swallowtail butterflies. PloS one, 10(10), e0141882.