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Show 301 APPENDIX H 11. REPORT ON THE ALPINE INSECT FAUNA OF COLORADO AND NEW MEXICO, SEA80N OF 1875, BY LIEUT. W. L. CARPENTER, NINTH INFANTRY. UNITED STATES ENGINEER OFFICE, GEOGRAPHICAL SURVEYS WEST OF THE 100TH MERIDIAN, Washington, D. C, May 1,1876. SIR: I have the honor to submit a report on the alpine insect fauna of Colorado and New Mexico. A separate entomological collection was made during the season of 1875, at high altitudes, which has proved of interest in its relation to geographical distribution and in the production of many rare and new species. It is to be hoped that future collectors will not overlook this important field for zoological research, but will endeavor to increase our limited knowledge of the insects of this region. Very respectfully, your obedient servant, W. L. CARPENTER, First Lieutenant Ninth. Infantry. Lieut. GEO. M. WHEELER, Corps of Engineers, in Charge, The mountain- ranges of the world produce a fauna of remarkable interest in its bear ing upon the discussion of geographical distribution and the existence of varietal forms which have resulted from the great climatic changes through which the globe has passed. In the elucidation of geological epochs, we find that even the lowest forms of life have a history which, could we but trace back through the dim ages which have intervened since the dawn of life, would throw a flood of light upon many subjects at present conjectural. When it is found that certain insects occur uniformly in the mount-aius of Asia, Europe, and America, at great elevations, and in British America at high latitudes, the geological significance of this fact becomes apparent; and the mind reverts to a period when the steady encroachment of a vast field of ice cauued the extinction of delicate species and compelled $ he survivors to change their habitat for lofty mountains, which had become islands in a sea of ice. Here, amid new conditions of temperature and a modified flora, a few hardy species were perpetuated, which have preserved their alpine characteristics to the present time. Thus we find certain insects on Mount Washington, New Hampshire, which are lost eight of as we journey westward through the ^ reat expanse of valley and plain to the foot of the Rocky Mountains; as we ascend them and approach the verge of the alpine flora, these same species re- appear with wonderful regularity, establishing the perfect identity of the in sect- fan Da of onr mountains. With the return of a genial climate, during the Champlain period, the ice receded to the north, releasing the fauna from its imprisoned state, and stimulating all life to again spread over the continent. The valleys and plains were once more filled with species which found the warmth of the new climate congenial to their tastes; these, spreading over the land and mingling with other forms which followed the retrogression of the ice from its southern limit, produced the fauna as it now exists. Other species, to which a boreal climate had become agreeable, finding the increasing temperature of the valleys distasteful, migrated to the northward in the path of the ice, which was slowly uncovering the country, until they found a suitable habitat in the arctic regions. Tbe few species which remained upon the mountain- peaks lingered about their old liaonts until the climate which we now have had become established and their retreat accordingly prevented. They are thus imprisoned in the mountains, contented with a modified climate so nearly resembling that voluntarily chosen by their relatives which have colonized the barren ground of the far north. Consequently we find these species dwelling in an extremely isolated range, although having a geographical distribution only dependent upon a requisite elevation above the level of the sea, or an equivalent high latitude and consequent congenial climate. The alpine insect fauna of America should then be regarded as but a fragment of that which survived the geological changes which occurred at the close of the Tertiary and beginning of the Quaternary epochs. Although the mountaiu genera and species are nearly all represented in the arctic fauna by the same species or their analogues, yet the number inhabiting the latter region is greatly in excess of the former, as would naturally be supposed in view of the general migration of the alpine fauna, set free by - the northward movement of an isothermal zone. With such similarity existing between them, the study of both fauna; becomes necessary in instituting any comparison between individuals of the same species for the purpose of detertniuiug varietal differ- |
