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Popular Science Monthly/Volume 86/March 1915/Insects of the Pacific

< Popular Science Monthly‎ | Volume 86‎ | March 1915


WHEN one speaks of the insects of the Pacific, they are the insects of the Pacific shores and Pacific islands that one refers to. For with all the amazing adaptiveness of insects to variety of habitat and habit, and with all the pressure of enormous numbers of species and individuals to drive them far and farther and into all the available places of earth, the insects have, curiously, so far not invaded the oceans. Although they constitute of known living animal kinds a full two thirds, perhaps three fourths, they are restricted in habit to but one third part of the earth's surface, to wit, its dry land and fresh and brackish waters. The real salt sea is tenantless of insects. A few long-legged surface treading kinds are found on ocean waters far from land, but these are really inhabitants of surface sea-weed patches, which, like their freshwater cousins, the familiar water-striders or skaters of ponds and quiet stream-pools, can run or glide quickly over the water's surface, denting but not breaking the supporting surface film.

There are also a few small kinds which haunt the beaches and rocks between tide lines for sake of the rich harvest of food thrown up by the waves. Such a kind is a little long-legged fly with atrophied wings, which lives on the headlands of the California shore in the Monterey Bay region. When the tide is out it runs actively about, looking like a small slender-bodied spider, over the rough, damp rocks between tide times, seeking bits of organic matter thrown up by the waves that dash over the rocks at high tide. When the waters come back these odd little flies seek refuge under small silken nets they have spun across shallow depressions in the rocks. They cling desperately to the under side of the protecting silken mesh, while the great waves dash and break over them. Of course they are much of the time actually submerged in salt water. But they stand it.

Recently a similar and closely allied fly has been found on the shores of bleak South Georgia Island in the South Atlantic about 500 miles east of Patagonia. And another tide-rock fly of like habits is known from the cold and tempestuous Kerguelen Island of the South Indian Ocean.

The insects of the Pacific Islands are, however, more conspicuous by the kinds familiarly known all over our continent than by the sorts peculiar to the islands. In fact, what with the same old house-flies and blue-bottles, mosquitoes and fleas, cockroaches and bedbugs, and other familiar close companions of man, the insect fauna of a Pacific island or of the Pacific coast of America is likely to be disappointingly familiar and familiarly troublesome.

But this familiar character of the first seen and most often seen insects of the Pacific points an important moral to the student of insect distribution and of insect troubles. It is the moral of man's personal aid in the wide dissemination of insect pests. Wherever he goes, by wagon, train or ship, he carries the pests with him, colonizes them wherever he settles, and supports them in their new homes by his own presence and the presence of his domesticated animals, Ms quickly planted grains and vegetables, fruits and flowers.

So the casually inquisitive visitor to Pacific lands will find himself irritated by the same kind of fleas, mosquitoes, buzzing flies and biting flies, nocturnal bed-fellows, the same old croton bugs and black beetles and the rest that he knows in the east and middle west.

They have all come to California and Oregon and Washington, and gone on to the Hawaiian and Samoan and Philippine Islands, just as many of them came from Asia to Europe and Europe to the Atlantic and went on to the Mississippi Valley in earlier years. And this emigration and immigration by the side and with the aid of man accounts for a considerable and, from the economic point of view, a very important part of the Pacific insect fauna. For most of the worst insect pests of California and the rest of the Pacific coast are imported and comparatively recently imported species.

The most important single group of insects to the citrus and deciduous fruit growers of California are the scale insects (Coccidæ), small, degenerate, specialized, wax-covered and protected sap-sucking creatures, of hardly the seeming of an insect at all. The San José scale, the cottony-cushion scale, the black scale, the soft brown scale, the red orange scale, and all the rest of the scaly crew are ever threatening clouds on the fruit-grower's horizon. And he spends annually much time, energy and money in fighting back the swiftly multiplying hordes of these pests.

Now practically all of them are natives of other lands; they are man-aided immigrants into California. The San José scale, that once threatened the whole deciduous fruit interest of California, came from China about 1875. The cottony-cushion scale that similarly once threatened all the citrus orchards came from Australia about 1868. And the story of the coming, and settling, and finding the country good, of several of the other kinds is as well known.

But, fortunately, the economic entomologists have learned something to their advantage from this kind of insect immigration. They have learned deliberately to hunt for and import good bugs to fight the bad ones. For example, it was discovered that the Australian cottony-cushion scale, so dangerous a pest in this country, was not so dangerous in Australia, and this because of the active efforts made there by a certain kind of little black-and-red lady-bird beetle known as the vedalia. The scale pest had got carried to America without its vedalia enemy, and, accordingly, found California in truth the promised land. Now what more common-sensible than deliberately to import and colonize vedalia in the California orange and lemon orchards? Which was, accordingly, done, and done easily and successfully, so that here, as in Australia, vedalia keeps the cottony-cushion scale insect within practically harmless bounds.

Naturally such a success has led to many other attempts in many other similar cases. Perhaps no other success has been so marked as the now classic first one, but much other success there has been, both on the Pacific coast and on Pacific islands, notably Hawaii, and also in the eastern states. The great fight against the imported foliage and forest tree pests of New England, the direful gipsy and brown-tail moths, is resolving itself more and more into a search for and colonizing of their natural parasites in Europe and Japan.

Another type of good bug brought to the Pacific coast by deliberate importation and carefully nursed to an effective colonization is the curious little fig-wasp, Blastophaga, by whose means the "caprification," i. e., pollination, of figs depends, on which depends, in turn, the full size, sweetness and the nutty flavor of the best commercial figs. The fig is a hollow but fleshy receptacle with many minute flowers inside. The Blastophaga eggs are laid in the ovules of these flowers, and there the tiny grub (larva) lives and feeds and changes finally into a little chrysalid, and then adult. The adult male Blastophaga is a curious deformed wingless creature, and remains in the fig of its birth until it dies. But the female is a winged active insect that leaves its natal and cradle fig and flies to others to lay its eggs. Curiously, it can find suitable egg-laying places only in the wild or so-called capri figs and so does not leave eggs in the cultivated figs, but in walking about over their flowers it dusts them with pollen brought from the fig last visited, and thus produces the necessary cross-pollination. As the Blastophaga lays no eggs in the domestic figs, it is necessary to keep a few wild fig-trees growing in or near the orchard.

But not all the Pacific coast insects are excessively bad bugs or excessively good ones. Some call for attention because they are just beautiful, or singular, or of unusual habit or habitat. And these are likely to seize the interest of most of us more certainly than the pests. For, after all, our interest in nature is not primarily one of dollars and cents. It is one of curiosity and of "wanting to know."

A matter that lends California's fauna and flora a special interest to naturalists is the peculiar biogeographic situation of the state. Biologically, California is essentially a large island, shut off by barriers of actual water on one side and by hot desert and high cold mountain ranges on the other, with the ends also nearly similarly barred by desert 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 Pacific coast. Three species occur in California, of which two are common and constantly met with. One (Termopsis augusticollis) is unusually large, and makes its communal nests in fallen pine-trees, telegraph and telephone poles and other dry wood. I have found colonies containing thousands of individuals in fallen trunks of the great trees of the Sierran forest.

Another group of interesting insects unusually well represented in California are the gall-flies (Synipidæ) which form the galls, or, better, stimulate the trees to form the galls, on oaks. Seventy species of these odd little flies have been listed for the state, and there are others in Oregon and Washington, As each species has its own special kind of gall, the oak-trees of the Pacific coast often bear a curiously variable load of "fruit" besides the acorns.

I should like to speak of some of the west-coast insects of unusual appearance or pattern, the kind that catch the eye of the most casual traveler, such as the giant, tarantula-killing, bronze-winged, blue-black Pepsis wasp, that indulges in battles-royal with the big hairy tarantulas and trap-door spiders, which themselves, though not insects, are near enough related to them to warrant mention in any account of our insect fauna. But I may not. I may not speak for them at all except to say that California will match its insects against the similar fauna of any other state for interest and opportunity for fascinating observation and profitable study.