National Geographic : 1936 May
WHO'S WHO AMONG THE BUTTERFLIES By AUSTIN H. CLARK United States National Museum BUTTERFLIES seem carefree crea tures, but they have a special duty to perform. That duty is to produce eggs and scatter them far and wide on the proper food plants so as to insure the largest possible crop of baby butterflies, or caterpillars. All their efforts, all their emo tions-and they are many and diverse have to do with the proper performance of this duty. We are prone to think of butterflies as dainty ornaments of woods, fields, and gar dens, where they flit about sipping nectar from the flowers. But feeding is a minor occupation with them-in most cases more of a diversion than a necessity-and many do not feed at all, or at least do not feed on flowers. The caterpillar does the feeding, both for itself and for the butterfly into which it turns, leaving the latter free to devote itself to the perpetuation of the race. BUTTERFLIES ARE JEALOUS We look upon butterflies as the most harmless, as well as the most conspicuous and attractive, of all those very numerous creatures known as insects. But, actually, many male butterflies are exceedingly jealous and aggressive. They fly viciously at each other and at insects or even small birds that cross their path. Usually this belligerent spirit is aroused by intrusion into the domain-a strip of roadside, a section of a wooded road, or the vicinity of a particular branch of a tree or bush-that a certain male regards as his rightful property. Some kinds have special dueling grounds to which they retire when in a fighting mood. And many "fight" wherever they may chance to meet. Such a "fight," of course, is really a game of bluff , as butterflies are so delicate that they would quickly incapacitate themselves if they met in rough physical combat. Among the less belligerent kinds pressure of population frequently is relieved by mi gratory flights often including many millions of individuals. The most famous of the migrants is the common Monarch, or Milkweed Butterfly (Danais plexippus). In the late summer it is often seen in enormous flocks, includ- ing both sexes equally, sometimes "mil lions filling the air for several hours to a height of 300 to 400 feet," or in "great swarms thick enough to cast a shadow" from 40 to 200 feet up (see pp. 670-671). These flocks usually fly in a southerly direction, and there is no real evidence that the butterflies ever return. This insect many times has been reported from Europe. It has been seen at sea 60 miles off Cape St. Vincent, Portugal, and many individuals have been caught in England. Migrations, more or less spectacular, are regularly, frequently, or occasionally under taken by a considerable number of different kinds of butterflies, including several of the common ones. These migrations, and the other curious habits of these insects, have received relatively little study, and we yet have much to learn about them. Butterflies represent only a small section of the scaly-winged insects, or Lepidoptera, which include five times as many moths. Nature does not distinguish butterflies from moths; indeed the skippers, usually placed among the butterflies, might just as well be considered moths. Most butterflies are attractively colored and fly in the bright sunlight, and most moths are dull and fly by night. Conse quently, we have a friendly feeling for the former and like to believe that they differ from the latter much more than they really do. Butterflies fall naturally into six different groups, in each of which the eggs, cater pillars, and pupae have their own special features, just as do the adult butterflies. Representatives of all these groups, and of many of the subgroups into which they are divided, are shown in the accompanying Color Plates (see also text, page 692). Brush-footed Butterflies (Nymphalidae) Largest of all the groups is that including the so-called brush-footed butterflies. In both sexes, though especially in the males, the legs of the first pair are much smaller than the other four, and are not used for walking. They are usually thickly clothed with long hairs and are kept closely folded against the body, so that the insects seem to have only four legs.