National Geographic : 1958 Jun
Ghostly Butterflies Perch on an Immortelle Tree THE GORGEOUS scarlet-flowering bois immortelle (Erythrina micropteryx) is one of Trinidad's most abundant trees as well as its showiest. At first glance it would seem to have some of the hallmarks of a weed; it is often seen as a wild plant growing in cultivated fields, a plant out of place. This species of immortelle was imported from Peru many years ago, but unlike the majority of such introductions it has found a place for itself as both a useful and an esthetic addition to the Trinidad flora. As we fly over the island, great areas of these blossoming trees come into view. Each tract marks the outline of a cacao plantation, for which the majestic trees provide necessary shade. They well deserve the local name madre de cacao. Spiny Armor Discourages Monkeys The niche that immortelles have won for themselves is an interesting one. The color of the blossoms and their lack of odor com bine to make them lonely at night, for moths or other nocturnal insects are more attracted to lighter-hued, scented flowers. Through the years a full-grown tree may reach a height of 80 to 90 feet, with a trunk armed with serried spines. Such an array is an effective barrier to monkeys and other arboreal creatures. This insulation against predators is a boon to the caciques, or giant orioles, that live in colonies and fasten their pendulous nests to the tips of lofty branches. With consummate but instinctive skill the orioles attach their finely woven five-foot nests in safety, out of the reach of all but winged enemies. With most of these latter they can cope by sheer weight of numbers and fighting ability. Less successful is their resistance to the parasitic giant cowbirds, which haunt the tree and seize every opportunity to lay an egg in the caciques' nests. Hummingbirds appear with the first bloom and remain until new green leaves replace the flowers. These visitors, together with passing butterflies, make a scene of superb color. The background is the tropical blue sky; then comes the coral and scarlet of the solid mass of bloom, unshaded by a single green leaf. The hummingbirds dart back and forth like iridescent bits of molten meteors. They vary from the hermits, with long, flowing tail feathers, to the diminutive tufted coquettes, less than three inches over-all and wearing Elizabethan ruffs of cinnamon and emerald on the sides of their heads. 842 Butterflies of endless shapes and colors add to the chromatic pattern. Their visits to the trees are brief, however, for the long flower tubes leading to the nectaries are gauged for the tongues of hummingbirds rather than those of butterflies. Color is present in almost every part of our terrestrial globe, and in the animal world may be fraught with life and death, playing a vital role as warning or protection. But there are two vast areas on the earth which are com paratively colorless-the ocean and the air. A host of oceanic creatures have taken ad vantage of this clarity and have themselves become transparent. Certain snails, worms, crustaceans, jellyfish, and fish have evolved a freedom from color and opacity. Many fish are revealed only by their silvery iridescence, the food they have swallowed, their faint shadows, or an unaccountable swirl in the water. There is no need for the scientist to dissect such crea tures; every organ and tissue is ready for direct study. What of the transparent sea of air in which we live and move and breathe? What a marvelous thing would be a transparent bird or bat, or even a translucent eagle. But the air is too thin to support heavy bodies with out substantial lifting limbs. Only by sturdy wings can animals attain flight through the air, temporarily conquering gravity. Insects with Transparent Wings Insects alone have evolved wings so large and bodies so small that transparency is pos sible. Several families of butterflies have ac quired transparency by a modification of the color-bearing scales. In some these are reduced in size or in numbers, in others they are changed to fine hairs or are actually set on edge like open slats of a Venetian blind. Or the scales may become transparent themselves or be so loosely attached that they soon fall off, to reveal the clear membrane beneath. Such a variety of adaptations only increases our wonder and bewilderment at the intricacy of nature, whether in the colorful immortelles and hummingbirds, or in the glasslike trans parency of jellyfish and butterflies. The wings of these casual butterfly visitors to our immortelle tree are transparent because the scales are reduced to minute hairs. Their full name is the "transparent one of the for est," or, as the scientist would put it, Ithomia drymo pellucida.