The History of the European Fauna

by R. F. Scharff

On the whole, the number of mollusca which we might point to as having migrated to Europe is not large, the great majority being indigenous to our continent. However, some of the other groups of invertebrates differ very materially in that respect from the mollusca. I cannot leave the consideration of the mollusca without referring to the fact that there appears to be a very important centre of distribution in South-eastern Europe. It is from this centre that many species have spread north and south, east and west. Take, for example, the genus Clausilia, a small land-shell shaped like a pointed round tower, and abundant on old walls and tree trunks. In England we have four species of Clausilia, in Ireland only two. In the greater part of Spain only our common Cl. bidentata occurs. As we go east the number of species rapidly increases. A maximum is reached in South-eastern Europe, where hundreds of different kinds are found. Towards Northern Europe a similar decrease of species takes place. So far the history of the Clausiliæ seems perfectly simple. An active centre of origin appears to exist in South-eastern Europe, from which the species radiate out in all directions. But when we come to look more closely into the extra-European distribution of the genus, and especially when we examine its past history, we find that its origin is extremely complex, and dates back to a much more remote period than would have been imagined, had we merely taken into account its present range in our own continent. Professor Boettger, who is the highest authority on Clausilia, tells us that the genus is known from the earliest deposits of the Tertiary Era. About 700 species are now known, and these have been sub-divided by Professor Boettger and others into a number of sub-genera. Some of these are extinct, but the great majority are still living. The sub-genus Phædusa occurs in the eocene and oligocene of Southern Europe, but it is extinct as far as our continent is concerned. Close upon a hundred species, however, still inhabit India, the Malayan Islands, China, Ceylon, and Japan. Then again, the sub-genus Laminifera occurs in the oligocene and miocene of Central Europe, and survives in a single species, Cl. Pauli, in South-western France. The groups Garnieria of China, Macroptychia of East Africa, Boettgeria of Madeira, and Nenia of South America, have no fossil representatives. We have here some very remarkable cases of discontinuous distribution which testify to the antiquity of the genus, and this is certainly confirmed by the fossil evidence. However, it is hardly likely that the headquarters, as it were, of Clausilia have always been in South-eastern Europe. Most of that part of the Continent has been submerged since eocene times more than once. The peculiar distribution of the genus might be explained, I think, if we supposed the original home of Clausilia to have been in Southern Asia, that from this centre Southern Europe was colonised, where a new centre developed in oligocene and miocene times, sending colonies off to Madeira and across the old land-connection which united Northern Africa and South America about that time. The most active centre of development then gradually shifted eastward again, while the older centres were perhaps submerged during the physical changes in the distribution of land and water.

I should have mentioned that the species wandering westward and northward from this South-European centre of distribution, would naturally have joined the migrants which came from beyond the borders of our continent. They might thus appear to be true Oriental migrants, and on a previous occasion I grouped all these together under the term of "Southern Fauna," as I assumed the observer to be stationed in the British Islands. All new-comers from the south-east, south, or south-west of Europe would be to him southerners quite irrespective of their original home, which might be in Southern Europe, Asia, or Africa.

The Swallow-tail is well known to all collectors of Butterflies in England, though it has of late years become very rare and is now confined to a few localities in the east of England. The members of the family Papilionidæ, to which it belongs, are mostly large and striking species, and their distribution is therefore more accurately known than that of the smaller and less conspicuous butterflies. Only four different kinds of Swallow-tail Butterflies inhabit Europe, but in Southern Asia and the Malay peninsula they attain their maximum as regards numbers; and there we find a great many species of this genus Papilio. Of the four European species only one, viz., Papilio hospiton, is peculiar to Europe; all the others range into Asia. It would seem, therefore, as if this genus was an Asiatic one and had migrated to Europe, and that the route taken was the one from Asia Minor across to Greece. We have a similar case in the closely allied genus Thais two of the three European species living also in Asia Minor. Thais cerisyi inhabits some of the Greek islands, as well as the mainland of Turkey and Greece.

Another genus of the great family Papilionidæ with which most lepidopterists are well acquainted is Parnassius. What butterfly-hunter has been in Switzerland without hearing of, or seeing, the famous Parnassius Apollo? We have four European species of Parnassius, only one of which is peculiar to our continent, but the locality where it occurs, the Caucasus, is on the borders of Asia. Almost all the other species are Asiatic, none however range to the south. Its headquarters, and I think its original home, are the mountains of Central Asia. From there it has spread—some species to the Himalayas, and a few to Europe and North America. But these migrations are not of very recent date. Parnassius no doubt arrived accompanied by a large number of other Central Asiatic mountain insects and plants. I shall refer to the latter again when dealing with the origin of the Alpine fauna, but meanwhile it might be mentioned that the famous Swiss "Edelweiss" (Leontopodium alpinum), which we are accustomed to regard as a typical Alpine plant, is certainly of Asiatic origin. In some parts of Southern Siberia it is one of the common meadow-flowers, and ranges from there south into Kashmere, but not northward. Like the Apollo, it does not occur in Scandinavia or Northern Siberia. Both plant and insect evidently migrated from Central Asia, directly westward along the southern border of the sea, which extended from that region as far as the European Alps in early Tertiary times. At that time the Caucasus was possibly still connected with the Balkan Mountains, across what is now the Black Sea, and that may have been the highway on which they travelled west.

Some of the Clouded-Yellows—butterflies appertaining to the genus Colias—formed part of the Oriental migration. The genus is undoubtedly of Asiatic origin, and while many of the species have turned northward, ranging across Siberia and North America, others have taken a southern and westward turn and thus reached Europe. We have two Clouded-Yellows in Western Europe, and both of them must have come with this migration.

A very good example of an Oriental migrant is Danais chrysippus, a magnificent butterfly found in Greece and Southern Italy. In Asia it is known from Syria, Persia, and from the whole of the southern portion of the Continent. The genus Danais (in its wide sense) is a large one, and principally occurs in the warmer regions of Asia. Three species are found in North America and only one in Europe.

Among the beetles belonging to this migration, there is one of very considerable interest from a distributional point of view, for all the species of the genus—even the whole family to which the genus belongs—are what is known by zoologists as "Commensalists." These are animals habitually associating and living in close connection with others with which they are not tied by any family relations or kinship. Such a state of close and permanent friendship is called "commensalism." Now it appears as if the members of this family of beetles (Clavigeridæ) had of their own free will formed such a close connection with colonies of ants—sometimes with one species, sometimes another. They are the permanent guests of the ants, and in return they secrete a fluid which is apparently highly prized by them. All of the Clavigers are provided with peculiar club-shaped antennæ, with which they ungraciously beat their hosts, when they are in want of food. According to some authorities, they even occasionally gnaw at the pupæ and larvæ of the ant with which they live.

Such beetles naturally can only have extremely limited means of distribution, and they are comparable in that respect with the woodlice of the genus Platyarthrus, to which I have already had occasion to refer. All the species of Claviger are confined to Europe, chiefly to the south, but one species, Cl. testaceus, has wandered farther north and occurs in the nest of the ant Lasius flavus in the south of England, Ireland, and Scotland. Though none of the Clavigers can be claimed as Oriental migrants, the centre of distribution of the genera belonging to the Clavigeridæ is in Southern Asia, and it is probable that the ancestors of the European Clavigers have spread westward from that region to Europe, eastward to Australia and Japan, and southward to Madagascar and South Africa. The genus Hopatroides, belonging to the same family as the so-called Spanish-fly (Tenebrionidæ), has twelve species in Western Asia and Greece. One only, H. thoracicus—an instance of discontinuous distribution—occurs in Andalusia. Amphicoma is represented in Western Asia and the Balkan peninsula by fifteen species, while three others are met with in North-west Africa and Southern Spain.

A genus of Dragon-fly, Onychogomphus, has in Europe a somewhat similar distribution to Claviger, but it has besides a very extensive foreign range. There are altogether thirty-five species; of these ten are Holarctic, twelve Oriental, five Mascarene, and eight Ethiopian. The centre of distribution is therefore in the Oriental region, and we may assume that in all probability the genus has originated there, the European species having travelled west with the Oriental migration at an early date of the Tertiary Era.

Ryothemis, another genus of Dragon-flies, has originated perhaps somewhat farther east than the last, for no less than thirteen species are found in Australia, a like number in India, five in Madagascar and Africa, and five in the Holarctic region. Both of these genera are entirely absent from America, and they have possibly travelled to Europe together.