For butterflies, as for Bedouins , nomadic life is harsh...
As a specialist on the butterflies of Arabia, I am accustomed to people saying, "But surely there are no butterflies in Arabia!" In fact the Arabian Peninsula is full of butterflies: no less than 130 species.
It is true that the majority of these species live in the mountainous regions -'Asir, Yemen, Hadhramaut, Dhofar and northern Oman - but even the desert regions have their permanent residents. Both H. St. John Phil by and Bertram Thomas caught specimens right in the heart of the Rub' al-Khali, Saudi Arabia's vast sand desert - species such as leopard butterflies.
More importantly, Arabia, standing as it does astride the zone of contact among three of the major zoological regions of the world - the African, the Oriental and the temperate - is, for fauna, a crossroads.
Like the fauna of any area, Arabian butterflies are the result of two factors: where they originated and how they adapt to the climate. Because the climate of Arabia fluctuated considerably during the last two million years or so, the composition of the butterfly fauna varied accordingly. As recently as 7,000 years ago (See Ammco World, March-April 1980), Arabia had a cooler, more humid climate, and though conditions have since become more rigorous, many of the species which first appeared in Arabia - or "colonized" Arabia, as lepid-opterists say - still survive. They provide living testimony to the successive waves of colonization which took place so long ago.
A million or so years ago, for example, the temperate fauna of the Himalayas made contact with those of the African highlands, and in Yemen still there exist a few butterflies which were established then. The small copper butterfly is one example; it has been separated for so long from other populations of the same species that it has acquired a special color pattern. As a result, a small copper from Yemen can be told from other small coppers at a glance. Much more recently, there was contact between the fauna of the Omani mountains and those of neighboring Iran - as proved by the discovery of the white banded rockbrown species in Oman a few years ago; it does not differ at all from the form which flies in Iran and Baluchistan. I am certain that in more humid times there must have been more species of this group in Oman, but increasing aridity and temperature forced them into extinction. It is almost possible to imagine how they were gradually pushed up the mountains in search of cooler and moister climates till they finally had no option left and disappeared, almost literally, into thin air.
The temperate-region butterflies, however, are no longer the most prominent component of the fauna. For the peninsula as a whole, it is the desert-adapted species and those of tropical origin which hold pride of place. The desert species - such as the desert white - are by no means numerous, but they are the only residents of the driest regions and their finely tuned survival mechanisms are fascinating.
Some butterflies, for example, spend several years as pupae - that is, in an immobile and non-feeding stage - waiting for the day when conditions are right for breeding; they then emerge and mate and lay eggs; in a matter of weeks the next generation also reaches the pupal stage. And some members of the blue butterfly family turn into cannibals if food supplies dry up, thus ensuring that at least a few specimens survive even the most disastrous season. As to the tropical species of butterflies in Arabia, most are allied to butterflies of the African region, though there are a few species of Asian origin as well. Papilio demodocus, for example, is an African butterfly which is common from Jiddah to Aden and Dhofar; the almost identical Papilio demoleus is common in oases in eastern Arabia, but its main population is spread all over Asia and Australasia. Furthermore - a fascinating fact - their Arabian distribution does not overlap as far as lepidopterists know. Some of the species of African origin have managed to penetrate as far east as India and Burma, but the majority are limited to southwestern Arabia. There is evidence that the African species of butterfly in Arabia are the survivors of several invasions, some of which probably date back a very long time; certainly a number of species have been isolated in Arabia long enough to develop into distinct species; related to African species, to be sure, but clearly distinct. The Arabian mistletoe butterfly is a good example.
Each of these groups of butterflies tends to be linked to special ecological conditions, especially to plants, and many have become closely adapted to a special environment. Thus the striped white is a temperate species which, in Arabia, is only found along the east coast, but has a desert counterpart which is almost indistinguishable. The range of these two species in Arabia does not overlap at all.
There are also butterflies, however, which have not specialized, yet also survive. They are the migrant species and their survival strategy is based on mobility. Put in simple terms, they're nomads who travel endlessly in search of conditions where they can breed.
One example is the painted lady, the world's most cosmopolitan butterfly. When this species has a successful brood, individual butterflies fly off in all directions and may travel thousands of miles. Thus if some wadi in central Arabia is suddenly blessed with an abundance of rain, some specimens of the painted lady will almost surely come across it, breed and lay their eggs. But their progeny will in turn leave the wadi, so if the wadi is not suitable for breeding again for many years, it won't matter; the progeny will have found still other places to breed.
Obviously many butterflies die in such a process; for butterflies, as for Bedouins, nomadic life is harsh. But the species will survive.
There are also less regular migrants than the painted lady. Small cabbage whites, for example, often invade the oases of eastern Arabia in the spring; although they are all finally killed off by the extreme heat of mid-summer, they breed first.
Characteristically, the painted lady and other migrants are less specialized in choice of food plant and ecological conditions than most of the sedentary species. They can't be as fussy and survive. And as a general rule migrant species - or species with considerable powers of dispersal - predominate in the harsher environments. Probably half the butterflies found in and around Riyadh are more or less dependent on migration for survival.
Butterflies, then, not only exist in Arabia, but flourish. And because they, like other fauna - and flora - in Arabia have learned to survive, they are of extraordinary interest to the zoologists and ecologists working on the secrets of the Peninsula's natural history.
Torben B. Larsen, a Danish economist, is the author of Butterflies of Lebanon and Butterflies of the Sultanate of Oman. He has discovered 22 new species and has written 30 papers on Middle Eastern butterflies.