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.