The Geographical Distribution of Animals, Volume 1 / With a study of the relations of living and extinct faunas as elucidating the past changes of the Earth's surface

by Alfred Russel Wallace

The third case is that of the same genera and even species of fish, and perhaps of frogs, in the two countries; which may be due to transmission from island to island by the aid of floating ice, with or without the assistance of more intervening lands than now exist.

Having arrived at these conclusions from a consideration of the vertebrata, we shall be in a position to examine how far the same causes will explain, or agree with, the distribution of the invertebrate groups, or elucidate any special difficulties we may meet with in the relations of the sub-regions.

Insects.

The insects of the Australian region are as varied, and in some respects as peculiar as its higher forms of life. As we have already indicated in our sketch of the Oriental region, a vast number of forms inhabit the Austro-Malay sub-region which are absent from Australia proper. Such of these as are common to the Malay archipelago as a whole, have been already noted; we shall here confine ourselves more especially to the groups peculiar to the region, which are almost all either Australian or Austro-Malayan, the Pacific Islands and New Zealand being very poor in insect life.

Lepidoptera.—Australia itself is poor in butterflies, except in its northern and more tropical parts, where green Ornithopteræ and several other Malayan forms occur. In South Australia there are less than thirty-five species, whereas in Queensland there are probably over a hundred. The peculiar Australian forms are few. In the family Satyridæ, Xenica and Heteronympha, with Hypocista extending to New Guinea; among the Lycænidæ, Ogyris and Utica are confined to Australia proper, and Hypochrysops to the region; and in Papilionidæ, the remarkable Eurycus is confined to Australia, but is allied to Euryades, a genus found in Temperate South America (La Plata), and to the Parnassius of the North-Temperate zone.

The Austro-Malay sub-region has more peculiar forms. Hamadryas, a genus of Danaidæ, approximates to some South American forms; Hyades and Hyantis are remarkable groups of Morphidæ; Mynes and Prothoë are fine Nymphalidæ, the former extending to Queensland; Dicallaneura, a genus of Erycinidæ, and Elodina, of Pieridæ, are also peculiar forms. The fine Ægeus group of Papilio, and Priamus group of Ornithoptera, also belong exclusively to this region.

Xois is confined to the Fiji Islands, Bletogona to Celebes, and Acropthalmia to New Zealand, all genera of Satyridæ. Seventeen genera in all are confined to the Australian region.

Among the Sphingina, Pollanisus, a genus of Zygænidæ, is Australian; also four genera of Castniidæ—Synemon, Euschemon, Damias, and Cocytia, the latter being confined to the Papuan islands. The occurrence of this otherwise purely South American family in the Australian region, as well as the affinity of Eurycus and Euryades noticed above, is interesting; but as we have seen that the genera and families of insects are more permanent than those of the higher animals, and as the groups in question are confined to the warmer parts of both countries, they may be best explained as cases of survival of a once wide-spread type, and may probably date back to the period when the ancestors of the Marsupials and Megapodii were cut off from the rest of the world.

Coleoptera.—The same remark applies here as in the Lepidoptera, respecting the affinity of the Austro-Malay fauna to that of Indo-Malay Islands; but Australia proper is much richer in beetles than in butterflies, and exhibits much more speciality. Although the other two parts of the Australian region (Polynesia and New Zealand) are very poor in beetles, it will, nevertheless, on the whole compare favourably with any of the regions except the very richest.

Cicindelidæ are not very abundant. Therates and Tricondyla are the characteristic genera in Austro-Malaya, but are absent from Australia, where we have Tetracha as the most characteristic genus, with one species of Megacephala and two of Distypsidera, a genus which is found also in New Zealand and some of the Pacific Islands. The occurrence of the South American genus, Tetracha, may perhaps be due to a direct transfer by means of intervening lands during the warm southern period; but considering the permanence of coleopterous forms (as shown by the Miocene species belonging almost wholly to existing genera), it seems more probable that it is a case of the survival of a once wide-spread group.