Moths of the Limberlost | Page 8

double membranes covered above and below with down. At the bases of the wings lie their nerves. The fore-wings each have a heavy rib running from the base and gradually decreasing to the tip. This is called the costa. Its purpose is to bear the brunt of air-pressure in flight. On account of being compelled to fly so much more than the females, the back wings of the males of many species have developed a secondary rib that fits under and supports the front, also causing both to work together with the same impulse to flight. A stiff bunch of bristles serves the same purpose in most females, while some have a lobe extending from the fore-wing. As long as the costa remains unbroken to preserve balance, a moth that has become entangled in bushes or suffered rough treatment from birds can fly with badly damaged wing surfaces.
In some species, notably the Attacine group and all non-feeding, night-flying moths, the legs are short, closely covered with long down of the most delicate colours of the moth, and sometimes decorated with different shades. Luna has beautiful lavender legs, Imperialis yellow, and Regalis red-brown. The day-flying, feeding group have longer, slenderer legs, covered with shorter down, and carry more elaborate markings. This provision is to enable them to cling firmly to flower or twig while feeding, to help them to lift the body higher, and walk dextrously in searching for food. It is also noticeable that these moths have, for their size, comparatively much longer, slenderer wings than the non-feeders, and they can turn them back and fold them together in the fly position, thus enabling them to force their way into nectar-bearing flowers of trumpet shape.
The abdomen is velvet soft to the touch, and divided into rings called segments, these being so joined that this member can be turned and twisted at will. In all cases the last ring contains the sex organs. The large abdomen of the female carries several hundred embryo eggs, and that of the male the seminal fluid.
Much has been written of moths being able to produce odours that attract the sexes, and that are so objectionable as to protect them from birds, mice, and bats. Some believe there are scent glands in a few species under the wing scales. I have critically examined scores of wings as to colour markings, but never noticed or smelled these. On some, tufts of bristlelike hairs can be thrust out, that give a discernible odour; but that this carries any distance or is a large factor in attracting the sexes I do not believe so firmly, after years of practical experience, as I did in the days when I had most of my moth history from books. I have seen this theory confounded so often in practice.
In June of 1911, close six o'clock in the evening, I sat on the front veranda of the Cabin, in company with my family, and watched three moths sail past us and around the corner, before I remembered that on the screen of the music-room window to the east there was a solitary female Promethea moth, that day emerged from a cocoon sent me by Professor Rowley. I hurried to the room and found five male moths fluttering before the screen or clinging to the wild grape and sweet brier vines covering it. I opened the adjoining window and picked up three of the handsomest with my fingers, placing them inside the screen. Then I returned to the veranda.
Moths kept coming. We began studying the conditions. The female had emerged in the diningroom on the west side of the cabin. On account of the intense heat of the afternoon sun, that side of the building had been tightly closed all day. At four o'clock the moth was placed on the east window, because it was sheltered with vines. How soon the first male found her, I do not know. There was quite a stiff evening breeze blowing from the west, so that any odour from her would have been carried on east. We sat there and watched and counted six more moths, every one of which came down wind from the west, flying high, above the treetops in fact, and from the direction of a little tree-filled plot called Studabaker's woods. Some of them we could distinguish almost a block away coming straight toward the Cabin, and sailing around the eastern corner with the precision of hounds on a hot trail. How they knew, the Almighty knows; I do not pretend to; but that there was odour distilled by that one female, practically imperceptible to us (she merely smelled like a moth), yet of such strength as to penetrate screen, vines, and roses and reach her kind a block away, against considerable breeze, I