National Geographic : 1958 Jun
Sleeping Butterflies Hang by Their Feet MANKIND, hummingbirds, and butter flies are diurnal, light-loving creatures. All spend the hours of the day concerned with the affairs of their lives, and all relax in sleep at night. In addition, all three classes are given to migration. In man it may be on a wholesale plan, as when the Goths swept southward through Europe and overwhelmed Rome. In the hummingbird it may be on the scale of a grand tour, annually from Alaska to Mexico, a round trip of several thousand miles. This is the more astonishing in a bird whose weight is scarcely that of a penny. Butterflies Migrate in Dense Clouds The migration of butterflies, in dramatic appearance, excels that of birds, for it takes place in the bright light of day and may num ber millions of individuals. The best known butterfly migrant is perhaps the monarch.* I have heard of a place favored by the flut tering hosts where to kill a monarch butterfly is to be threatened with fine and imprison ment. This, I regret to say, is not stimulated by entomological feeling but by the danger of losing remunerative tourist visits. Once, while riding with a party along a mountain trail in northern Burma, we entered an enormous cloud of golden butterflies, which alighted on our clothing, horses, and ourselves. I captured a few specimens for identification; my Burmese companions gently picked off the insects or carefully brushed them away, for they believed these butterflies to be the wan dering spirits of men who are asleep. A mass migration of butterflies is usually come upon suddenly, without warning. A few scattered golden yellows drift by, a skein of a dozen fly past, then abruptly the surround ing air is filled with them. For hours or for days the butterflies pass, in an uncountable fluttering swarm. A narrow-winged black butterfly with slashes of scarlet across the forewings may be the first to catch the eye or enter the net of a newcomer to the Tropics. Further ac quaintance reveals that it is a Heliconius, either melpomene or erato.t This tells us that 200 years ago the mind of Linnaeus, the natu ralist, turned to Greek mythology as he looked at the nameless butterflies before him. He thought of the muses of tragedy and of lyric poetry, and their home on Mount Helicon. This butterfly seems to have little fear of man or of other possible dangers. Seldom 844 rising higher than 20 feet above the ground, Heliconius flits through the open forest without ever brushing a wing against the mesh of vines, tendrils, and leaves. I watched one as it fluttered at sunset one day along a trail, sometimes almost brushing against me. It forged ahead and after a few yards I found it resting in a small spot of sunlight. Then a cloud obscured the light, and the butterfly flew to a cluster of leaves, where it began a curious pushing and butting with both body and wings. Suddenly, instead of one, there were four butterflies, three of the pendant leaves having changed into insects. Heliconius had led me, on its daily migration, to the sleeping place of its fellows. Search revealed eight more, and before long two newcomers came up the trail. As the dusk increased, more and more came, until I counted 49. Soon the fluttering ceased. I carefully picked one sleeper from its twig, and the legs let go without resistance. I put it back, and the feet again supported the insect. It had not awakened. Another I carried away a few yards and blew upon it with no result. It slept quietly. Then I shook and jarred it, and at once the body curved around, two tufts of hairs ap peared, and the air was filled with the odor of witch hazel. To a human this is a pleasant, clean odor, but it must be a potent defense against many enemies. Wanderers Return to the Same Twig What guides the butterfly to its sleeping place? It seems probable that locality sense plays the dominant part, but it is equally cer tain that odor is important. If we watch a particular butterfly, say one with a distinctive tear in its wing, we may find that it alights on the same twig and even the same part of the twig on successive evenings. It is not un common to see an incoming melpomene or erato waken and drive away one of its fellows and take its place on the perch. We have never witnessed the inception of a sleeping colony, but we have observed the ending. As time goes on the members become more bedraggled and worn, and finally the last insect fails to return. Then the dormi tory may lie empty until a new colony takes over the following year. *See "Butterfly Travelers," by C. B. Williams, NATIONAL GEOGRAPHIC MAGAZINE, May, 1937. t See "Keeping House for Tropical Butterflies," by Jocelyn Crane, NATIONAL GEOGRAPHIC MAGAZINE, August, 1957.