Page:Popular Science Monthly Volume 86.djvu/272

268 and mountain. This results in her showing the characteristics of an island fauna and flora, with their numerous monotypic plants and animals, unique, solitary kinds, developed in isolation and under special local conditions. California's insect fauna, therefore, includes many unique species and genera, and even a few families, not found elsewhere on this continent, not even in other neighboring states. This makes it an exceptionally happy hunting-ground for the insect-collector and systematist.

But not only does its biological isolation give an exceptional interest to its insect kinds, but its extraordinary topographic and climatic diversity introduces unusual and highly contrasted conditions in insect living and, through environmental influence, produces strange kinds of specialization of structure and habit. For example, the brave little butterflies (Chionobas) that live on the summits of the Sierra Nevada are bound to attract our attention, for their nearest cousins (other species of the same genus) are similar butterflies confined to the summits of the Rocky Mountains, 1,000 miles away, and Mt. Washington in New Hampshire and Mt. Katahdin in Maine, 2,000 miles farther. These lonely mountain-top butterfly kinds are good illustrations of the fact that altitude can replace latitude in distribution. And they undoubtedly owe their marooning on widely separated peaks to their neglect to follow the retreating glaciers of the close of the Great Ice time northward, remaining, instead, in these isolated alpine regions where conditions have remained practically glacial.

The California mountains, especially the Coast Range, have another especially interesting group of insect inhabitants in a curious small family of delicate, long-legged, stream-haunting flies called net-winged midges (Blypharoceridæ). Although scattered widely over the world in mountain regions, hardly more than a score of species are known, of which almost one half are peculiar to the Pacific coast. Their immature life is passed, as larva and pupa, in the swiftest and clearest of mountain streams, clinging by strong little sucking pads to the smooth rock bottom on the verge of a fall. The larvae die if they happen into slow or stagnant water, and many of the delicate flies are torn away by the current and lost as they emerge from the pupae. But, nevertheless, with all this restriction of life to certain narrow and dangerous conditions, the net-winged midges, like the water ouzels, near whom they domicile, maintain a successful existence to add to our interest in the mountain streams.

Another interesting group of insects, well represented in California and very sparingly elsewhere in this country or anywhere out of the tropics, is the family of termites, or white ants (Termitidæ). Indeed, out of the seven species known to occur in the United States, but one is found in the east, the other six being limited to the southwest and