The Geodephaga consist of two families, Cicindelidæ and Carabidæ, differing in their form and habits no less than in their numbers and distribution. The former, comprising about 800 species, are far more abundant and varied in Tropical regions; the latter, more than ten times as numerous, are highly characteristic of the North Temperate zone, where fully half of all the known species occur.
CICINDELIDÆ. (35 Genera, 803 Species.)
The Cicindelidæ, or Tiger Beetles, are a moderately extensive group, spread over the whole globe, but much more abundant in tropical than in temperate or cold countries. More than half of the species (418) belong to the single genus Cicindela, the only one which is cosmopolitan. The other large genera are,—Collyris (81 sp.), wholly Oriental; Odontochila (57 sp.), South American, with species in Java and Celebes; Tetracha (46 sp.), mostly South American, but with species in South Europe, North America, and Australia; Tricondyla (31 sp.), characteristic of the Oriental region, but extending eastward to New Guinea; Ctenostoma (26 sp.), wholly Neotropical; Dromica (24 sp.), wholly African, south of Lake Ngami and Mozambique; Therates (18 sp.), wholly Malayan, from Singapore to New Guinea.
The genera are distributed in the several regions as follows:—the Nearctic region has 5 genera, 3 of which are peculiar to it; the Palæarctic has 2, but none peculiar; the Ethiopian 13, with 11 peculiar; the Oriental 8, with 3 peculiar; the Australian 9, with 2 peculiar; and the Neotropical 15, with 10 peculiar. The connection between South America and Australia is shown by the latter country possessing 9 species of the characteristic South American genus Tetracha, as well as one of Megacephala. The small number of peculiar genera in the Oriental and Australian regions is partly owing to the circumstance that two otherwise peculiar Oriental genera have spread eastward to the Moluccas and New Guinea, a fact to be easily explained by the great facilities such creatures have for passing narrow straits, and by the almost identical physical conditions in the Malayan portion of the two regions. The insects of Indo-Malaya were better adapted to live in the Austro-Malay Islands than those of Australia itself, and the latter group of islands have thus acquired an Oriental aspect in their entomology, though not without indications of the presence of an aboriginal insect-fauna of a strictly Australian type. The relation of the Australian and Neotropical regions is exhibited by this family in an unusually distinct manner. Tetracha, a genus which ranges from Mexico to La Plata, has 9 species in Australia; while Megacephala has 2 American and 1 Australian species. Another curious, and more obscure relation, is that between the faunas of Tropical America and Tropical Africa. This is also illustrated by the genus Megacephala, which has 4 African species as well as 2 South American; and we have also the genus Peridexia, which has 2 species in South America and 2 in Madagascar.
Several of the sub-regions are also well characterised by peculiar genera; as Amblychila and Omus confined to California and the Rocky Mountains; Manticora, Ophryodera, Platychile and Dromica, characteristic of South Africa; Megalomma and Pogonostoma peculiar to the Mascarene Islands; and Caledonica to the islands east of New Guinea. The extensive and elegant genus Collyris is highly characteristic of the Oriental region, over the whole of which it extends, only just passing the limits into Celebes and Timor.
The Cicindelidæ, therefore, fully conform to those divisions of the earth which have been found best to represent the facts of distribution in the higher animals.
CARABIDÆ. (620 Genera, 8500 Species.)
The enormous extent of this family, necessitates a somewhat general treatment. It has been very extensively collected, while its classification has been most carefully worked out, and a detailed exposition of its geographical distribution by a competent entomologist would be of the greatest interest. A careful study of Gemminger and Harold's Catalogue, however, enables me to sketch out the main features of its distribution, and to detail many of its peculiarities with considerable accuracy.
The Carabidæ are remarkable among insects, and perhaps among all terrestrial animals, as being a wonderfully numerous, varied, conspicuous, and beautiful group, which is pre-eminently characteristic of the Palæarctic region. So strikingly and unmistakably is this the case, that it must be held completely to justify the keeping that region distinct from those to which it has at various times been proposed to join it. Although the Carabidæ are thoroughly well represented by hosts of peculiar genera and abundant species in every part of the world without exception, yet the Palæarctic region alone contains fully one-third, or perhaps nearer two-fifths, of the whole. It may also be said, that the group is a temperate as compared with a tropical one; so that probably half the species are to be found in the temperate and cold regions of the globe, leaving about an equal number in the much more extensive tropical and warm regions. But, among the cold regions, the Palæarctic is pre-eminent. North America is also rich, but it contains, by far, fewer genera and fewer species.
The magnificent genus Carabus, with its allies Procerus and Procrustes, containing about 300 species, all of large size, is almost wholly confined to the Palæarctic region, only 10 species inhabiting North America, and 11 Temperate South America, with one on the African mountain of Kilimandjaro. Twelve large genera, containing together more than 2000 species, are truly cosmopolitan, inhabiting both temperate and tropical countries all over the globe; but many of these are more abundant in the Palæarctic region than elsewhere. Such are Scarites, Calosoma, Brachinus, Cymindis, Lebia, Chlænius, Platynus, Harpalus, Bembecidium, Pæcilus, and Argutor. Of tropical cosmopolites, or genera found in all the tropical regions, but not in the temperate zones, there seem to be only four,—Catascopus, Coptodera, Colopodes, and Caasnonia. Pheropsophus is confined to the tropics of the Old World; while Drimostoma, though widely scattered, is characteristic of the Southern Hemisphere.