The Himalayan range extends in a great arc from northwest to southeast, across the northern boundary of the Indian subcontinent. The eastern part of the range is several degrees of latitude south of the western part. The southernmost part of the range is nearly 27 degrees North latitude and 90 degrees East longitude in West Bengal, India, while the northernmost part of the range is around 34 degrees North latitude and 75 degrees East longitude in Jammu and Kashmir, India. The western half of the range has a drier, more temperate climate than the eastern half, with greater Palearctic affinities, both in plants (Polunin & Stainton 1984) and butterflies (Evans 1932). Both the tree line and the snow line are lower in the western Himalaya than in the east (Polunin & Stainton 1984) and plant species that occur along the entire length of the range generally grow at lower elevation in the west than in the east (Brandis 1875).

57 (+/- 1) species of Papilioninae are known from the Himalaya east of Sikkim. Of these, 27 species have been recorded from the Himalaya west of Nepal.

In the present study, the altitudinal distribution of the Papilioninae fauna found west of Nepal has been compared with that of the same species in the eastern Himalaya.

Atrophaneura varuna White, Papilio alcmenor C. & R. Felder and Papilio helenus L. have not been reported from the western Himalaya for nearly a century since Hannyngton (1910) and are therefore excluded from the discussion. However, it is worthy of note that Hannyngton recorded alcmenor up to 2100 m elevation while in the eastern Himalaya it is known from 300 m (Arora & Mondal 1981) to 1800 m (Talbot 1939).

Materials and Methods

The altitudinal distributions of the Papilioninae species were obtained from three sources: the first, published literature; the second, unpublished notes compiled by my father, the late Fred Smetacek Sr. in Nainital district of the Kumaon Himalaya west of Nepal between 1949 and 1986 and the third, my own observations, mainly in the W. Himalaya, comprising specimens, field notes and the results of breeding experiments compiled since 1980.

The altitudinal distribution of the plant species mentioned was obtained from published botanical works. In all cases, the extreme altitude was taken, since these plants occur at different elevations in different localities. For example, since Zanthoxylum armatum DC (Rutaceae) ascends as high as 2100 m in Kumaon (Osmaston 1927) but to 2500 m further west in Kullu (Dhaliwal & Sharma 1999), I used 2500 m as the maximum elevation for the plant in the western Himalaya.

Results

The altitudinal distribution of the Leptocircini (8 species common to both halves of the Himalaya) was found to be practically identical in both areas. Of these, only subgenus Pazala Moore of Graphium Scopoli containing two or three species and Meandrusa Moore are restricted to a montane habitat. There is some confusion regarding the taxonomic position of Himalayan members of Pazala, so suffice it to say that they occupy a belt between 1600 m and 2600 m along the entire range, with stragglers descending to 900 m (de Nicéville 1894; Wynter-Blyth 1957) and ascending to 3300 m (Ebert 1966). In the western Himalaya, two species are found, namely Graphium (Pazala) eurous caschmirensis Rothschild and Graphium (Pazala) mandarinus garhwalica Katayama. Although there is a record for a member of the genus (“Papilio glycerion Westwood” = G. (P.) eurous vide Racheli & Cotton 2009)) being bred on Persea odoratissima (Nees) Kosterm. (Lauraceae) in Mussoorie, W. Himalaya (Robson 1895), I have only found G. (P.) eurous larvae on Persea duthiei (King ex Hook, f.) Kosterm. and Neolitsea umbrosa (Nees) Gamble (both Lauraceae), and both butterfly species entirely absent in areas where only P. odoratissima occurs in the Western Himalaya.

The remaining members of the tribe belong to Graphium (Graphium) Scopoli and are low elevation butterflies that inhabit the plains adjoining the hills and low outer ranges, with two species, G. cloanthus Westwood and G. sarpedon L. ascending to 2750 m even in the main range (Wynter-Blyth 1957). Recently, Singh (2006) discovered what appears to be an isolated population of Meandrusa lachinus Fruhstorfer in a moist temperate forest below the tree line in the Kedarnath Musk Deer Reserve in the Garhwal Himalaya, India. The type locality of the nominate subspecies is Darjeeling, West Bengal, India and Lachen-Lachung, Sikkim, India (Racheli & Cotton 2009), both in the eastern Himalaya, which are more or less at the same elevation as the Kedarnath Musk Deer Reserve in Garhwal.

The Palearctic Papilio machaon L. occurs in the Himalaya as far east as Sikkim (Gaonkar 1999). It is the only member of the subfamily that is found at higher elevation in the east than in the west. In the extreme west in Kashmir, it descends to 600 m, but is not found below 2450 m in Sikkim (Wynter-Blyth 1957). This distribution pattern is in keeping with classical views on the subject. It feeds on various umbellifers.

Papilio agestor Gray occurs throughout the range in a belt between 1200 m and 2600 m elevation, occasionally ascending to 2750 m in the western Himalaya (Wynter-Blyth 1957). It has been bred on Persea odoratissima (by Fred Smetacek Sr.) and Persea duthei (King ex Hook.f.) Kosterm. (Lauraceae) (mihi) in the western Himalaya.

Four species, Pachliopta aristolochiae Fabricius, Papilio polytes L., Papilio demoleus L. and Chilasa clytia L. are widespread on the Gangetic plain, which adjoins the Himalayan foothills. They are common along the entire length of the outer Himalaya, ascending to 1500 m with stragglers at 2250 m (Wynter-Blyth 1957; mihi).

The remaining ten species, comprising members of Troidini and Papilionini, were found to ascend with the latitude, occurring at low elevation in the eastern Himalaya and at higher elevation in the west (Table 1).

Concerning the larval host plants in the Himalaya, Zanthoxylum armatum is a known host plant of Papilio bianor Cramer and Papilio protenor Cramer. It grows between 610 m and 915 m in the eastern Himalaya and hills of N.E. India (Hooker 1872) and between 900 m and 2100 m in the Kumaon Himalaya west of Nepal (Osmaston 1927). Further west in Kullu, it ascends to 2500 m (Dhaliwal & Sharma 1999). Limonia acidissima L. (Rutaceae) is also a known host plant of P. bianor. This butterfly does not appear to use this plant in the western Himalaya, where it grows from the plains to 900 m (Osmaston 1927), but has been bred on it and probably uses it routinely in the eastern Himalaya, where the plant grows to 1200 m (Hooker 1872).

Bailey (1951) reported Papilio arcturus Westwood feeding on Skimmia Thunberg (Rutaceae) in the Kathmandu valley, Nepal. Recently, the eastern and western populations of Himalayan Skimmia have both been raised to species rank. The east Himalayan S. laureola Sieb. & Zucc, grows between 1500 m and ?3350 m (Brandis 1875), while the west Himalayan S. anquetilia Taylor & Airy Shaw grows between 2100 m (Osmaston 1927) and 3350 m (Brandis 1875; Osmaston 1927 gives 3200 m). These are nearly exactly the altitudinal limits given by Wynter-Blyth (1957) for arcturus in the respective areas, although the butterfly has not actually been bred on S. anquetilia in the western Himalaya so far.

Papilio paris L. has been bred on Euodia roxburghiana Bentham (Rutaceae). This plant does not occur in the west Himalaya although the butterfly does. In the hills of northeast India, this plant ascends to 1200 m (Hooker 1872). The larval host plant in the west Himalaya is still unknown, although Robinson et al. (2001) report a wide variety of rutaceous larval host plants from the eastern Himalaya, notably several species of Zanthoxylum, including Z. armatum, and Citrus L..

The Troidini are believed to be primarily Aristolochia L. feeders. Neither of the 2 known west Himalayan members of this plant genus has been reported from below 1950 m (Osmaston 1927; Gupta 1968). Byasa dasarada and B. polyeuctes Doubleday have been bred by Michael Green on Aristolochiaceae at Chamba in Himachal Pradesh, India (in litt, to Fred Smetacek Sr.). However, no botanical works record any Aristolochiaceae from Himachal Pradesh except Hooker (1885), who included a specimen of Aristolochia punjabensis Lace from there in the supplementary section of his work and Dhaliwal & Sharma (1999) who did not find the plant in Kullu but included it on the basis of Hooker (1885) with the observation “origin doubtful”. B. dasarada and B. polyeuctes are known from Kullu and even further west in Kashmir and Pakistan, while B. latreillei Donovan has been reported from as far west as Afghanistan (Bozano 2010) so they probably feed on the only known Aristolochia in that area, A. punjabensis.

Table 1.

Comparative altitudinal distribution of some Papilioninae in the Western and Eastern Himalaya.

Table 2.

Comparative altitudinal distribution of known and probable larval host plants of Papilioninae in the Western and Eastern Himalaya.

G. Flutsch (pers. comm.) found a Troides Hübner larva on Aristolochia dilatata N.E. Brown at 2400 m in the Binsar Wildlife Sanctuary in Almora district, Uttarakhand state in the west Himalaya. Since T. aeacus C. & R. Felder is the only Troides in the area, it is reasonable to assume that it was a T. aeacus larva.

I have found T. aeacus to be selective in the forests it inhabits. I bred it on A dilatata in the western Himalaya, feeding the larvae leaves only. However, Igarashi (1966) noted the predilection of the larvae for leaf stalks and stems, eventually consuming more stems and leafstalks than leaves in the later larval instars. I found final instar larvae of T. aeacus consuming the seed pods of A dilatata and must note that the individuals bred by me only on a diet of leaves emerged rather stunted. Having examined numerous plants of A. dilatata in different forests, I was struck by the fact that T. aeacus only occurs in forests where mature, seed bearing plants of A. dilatata grow, unlike the members of Atrophaneura Reakirt and Byasa Moore, that willingly lay eggs on and complete their life cycles on what may best be described as seasonal plants of A. dilatata, with up to 20 leaves during the summer months from April to June and a spurt of growth during the wet summer season from late June to September. Such plants, growing in dry upland locations, do not bear seed pods while plants growing near perennial water have stems up to 5 inches in circumference with hundreds of leaves and dozens of seed pods. Such plants support populations of T. aeacus.

The only resident, low elevation Troidine in the west Himalaya is Pachliopta aristolochiae Fabricius, whose larval host plant in the area is unknown. Seitz (vide Sevastopulo 1973) includes Piperaceae among the known larval hosts of this butterfly. Robinson et al. (2001) overlooked this latter record but report Dioscorea wallichii (Dioscoreaceae) as a larval host plant as reported by Beeson (1941). Certainly, Dioscorea is a common plant in the western Himalaya and might account for this butterfly's abundance at suitable seasons.

As an experiment, ten potted plants of Aristolochia dilatata were brought down from 2400m and placed in a garden at Bhimtal in the Western Himalaya at 1500m from July 2010 to June 2011. During this period, although at least 50 female Pachliopta aristolochiae flew past these pots and investigated nearby plants for flowers and larval host plants, none of these butterflies either investigated the A. dilatata plants nor oviposited on them. This shows that A. dilatata is not likely a larval host plant of Pachliopta aristolochiae and this factor perhaps limits its altitudinal distribution in the western Himalaya .In other parts of India and S.E. Asia, it has been reported to feed on at least 15 species of Aristolochiaceae (Robinson et al. 2001). It undoubtedly feeds on cultivated Aristolochia tagala Cham, plants at the foot of the hills, but this plant is not part of the original flora of the area, although the butterfly appears to have been present before the introduction of this plant. Therefore, it must feed on some other, wild, plant in the area.

In the eastern Himalaya, six species of Aristolochia occur (Hooker 1885; Polunin & Stainton 1984). Only one occurs in the temperate zone between 1800 and 2900 m (Polunin & Stainton 1984). The remainder occurs from low elevation to 900 m (2 species), 1200 m (1 species); 1500 m (1 species) and 1800 m (1 species). The 2 west Himalayan Aristolochia species do not occur in the east Himalaya (Table 2).

The larval host plants of Byasa latreillei and Papilio janaka Moore in the west Himalaya are unknown, although Igarashi (1966) bred them on Aristolochia griffithii Hook.f. & Thoms, ex Duchartre and Zanthoxylum alatum (=Zanthoxylum armatum DC) respectively in Nepal. A. giffithii does not occur in the western Himalaya and P. janaka does not appear to feed on Z. armatum in the western Himalaya. Rather, it appears to be restricted to patches of Zanthoxylum acanthopodium DC, although it has not actually been bred on this plant so far.

The altitudes assigned to species in Table 1 are for populations. Stragglers of the following species have been recorded at lower elevation in the western Himalaya: T aeacus (1200 m: mihi); B. latreillei (1500 m: Fred Smetacek's unpublished notes); B. polyeuctes: 1200 m: mihi); B. dasarada (1500 m: mihi); P. protenor, P. bianor and P. paris (all at 660 m: Roonwal et al. 1956; Singh & Bhandari 2003). Howarth & Povolny (1973) described B. latreillei afghana on the basis of two males recorded from 580 m elevation in Jalalabad, Afghanistan. These are the only two specimens known.

Discussion and Conclusion

It is generally accepted that on a north-south axis, temperate zone species tend to occur at higher elevation towards the Equator, while tropical forms tend to be found at lower elevation as we progress towards the poles.

In butterflies, montane species tend to occur in altitudinal belts. Such species are not generally found above or below their chosen altitudinal limits, although stragglers are occasionally encountered. Factors restricting the altitudinal distribution of species are not wholly understood. Among the factors believed to influence altitudinal distribution are the thermal tolerance of the butterfly, wing color and presence of the larval host plant.

Table 3.

Papilioninae with a pan-Himalayan distribution.

Table 4.

Papilioninae that do not exhibit anomalous altitudinal distribution in the Himalaya.

There seems to be a strong positive correlation between the altitudinal belt occupied by the various Papilionidae and their larval host plants in the west Himalaya.

While Ferris (1974) drew attention to the fact that different subspecies of a butterfly can occur in widely disparate habitats, in the case of Troides aeacus aeacus in the Himalaya, the same subspecies occurs in widely disparate habitats at either end of the mountain range. In the west, it is found in temperate and higher elevation subtropical forests and never in the tropical zone below 1000 m elevation, while in the east it occurs mainly in tropical forests at low elevation. Igarashi (1966) reported that in the Central Himalaya in Nepal, the species mainly inhabits lowland forests but occasionally was seen up to 3000 m elevation. Byasa dasarada, Atrophaneura aidoneus, Papilio janaka and Papilio paris also occur at low elevation in the east and higher elevation in the west.

In the case of T. aeacus, the presence of a suitable larval host plant appears to be the decisive factor governing its distribution. However, this is not necessarily the case with other birdwing butterflies. The Papuan Ornithoptera priamus L. and O. goliath Oberthur have been bred on Aristolochia tagala Cham. in Papua New Guinea (Borch & Schmid 1973; Straatman & Schmid 1975). This plant also occurs naturally in S. India, Sri Lanka and the E. Himalaya, where these butterflies do not occur.

In the case of Zanthoxylum armatum feeders such as P. bianor and P. protenor and Skimmia-feeding P. arcturus, the similarity in the altitudinal distribution of the butterflies and the plants is too striking to be ignored (Tables 3 & 4). Interestingly, P. protenor also feeds on Zanthoxylum acanthopodium in the western Himalaya and so occurs at higher elevation than P. bianor, which appears not to feed on this plant and is therefore found at lower elevation, as high as Zanthoxylum armatum occurs.

De Rhé Philipe (1931) and Wynter-Blyth (1957) noted the absence of B. dasarada and B. polyeuctes from the area around Shimla (= Simla) in the western Himalayan state of Himachal Pradesh, although both species are ubiquitous at suitable altitudes east, west and north of Shimla. Wynter-Blyth (1957) suggested that it was only a temporary phase and that both populations would eventually re-establish themselves and become common again. However, Collett (1921) did not find any Aristolochiaceae in the area around Shimla, which probably accounts for the absence of these butterflies from that area.

Besides the ten Papilionidae species mentioned in this paper, at least eight satyrine species and three nymphalines also ascend with the latitude on the Himalaya while one danaine and three satyrines exhibit the reverse tendency (Wynter-Blyth 1957). Unfortunately, very little is known about the larval host plants of the satyrines.

From the above, it is evident that a butterfly subspecies does not necessarily occur in the same type of habitat throughout its range; that a butterfly species' altitudinal distribution can increase with the latitude when, in the classical view, the opposite should be the case; and that the presence of a larval host plant can decisively influence the altitudinal distribution of a butterfly.

These observations in turn suggest that some butterflies possess a hitherto unsuspected ability to adapt to different climatic conditions; that such adaptation does not necessarily express itself in the colors or patterns on the wings in the form of melanism or otherwise; that Himalayan Troidini and Papilionini are generally only found more or less in the altitudinal belt of their larval host plants; that two major factors governing a butterfly's distribution are the presence or absence of a suitable larval host plant and the butterfly's ability or inability to adapt to the plant's habitat.

This still leaves unresolved the question why some plant species ascend with the latitude on the Himalaya, but that is beyond the scope of this paper. However, Hooker (1849) while referring to this phenomenon noted that the same tendency is exhibited in some plant groups in the high southern and Antarctic latitudes. In fact, he stressed the fact that the snowline ascends with the latitude in the Himalaya from 14,000 feet (4267 m) (in the eastern Himalaya) south of the Brahmaputra river in latitude 27 degrees N to 20,000 feet (6096 m) at the north western extremity of the range beyond the Sutlej river in latitude 36 and 37 degrees N. He pointed out that on the Himalaya, the range of tropical forms is extended upward to greater elevation and temperate forms descend to lower elevation, of which Rosaceae and Ericaceae are good examples. However, there is no accepted explanation why this happens.