The flight of insects is a fascinating phenomenon that has inspired much study by scientists. Insects are the only invertebrates that possess this capability. This enables them to exist in great numbers of environmental situations, so they are much more diverse than other invertebrates, with approximately one million species described.
The typical insect wing is a superbly designed flying tool. It consists of a thin membrane reinforced throughout with numerous veins, which results in a highly functional compromise between weight and strength. The anterior portion of the wing is stiffened with a heavy costal vein, and the wing then becomes thinner and more flexible toward the trailing edge. This structure is capable of a strong sculling action. This sculling action can be analogized by fanning air into a fire. 1 If one selects a flat board for the task he will find it quite ineffective. A small piece of rug held stiff on one margin, or a moderately flexible piece of cardboard is much more effective.
Insects that have two pairs of wings frequently join the anterior and posterior wings by means of hooks and grooves to create a single sculling unit as in the case of the Hymenoptera and many Lepidoptera. Insects such as the Odonata, which do not have their wings joined, over come the problem of air turbulence by beating the front and rear pairs alternately.
Complex wing movement
Wing movement in insects is complex, and consists of elevation and depression, fore and aft movement, pronation and supination (twisting), and changes in shape by folding and buckling. The wingtips describe a figure-8 pattern. Many insects can hover or fly backward by changing the angle of the figure-8.
Some of the very good fliers (Diptera, Hymenoptera, and some Lepidoptera) can fly sideways or rotate about the head or tail by employing unequal wing movement. Romoser points out that the wing movement of insects is so efficient that it produces a polarized flow of air from front to rear during 85 per cent of the wingbeat cycle. 2
Insects with a large wing area and a slower, fluttering flight such as Isoptera, butterflies such as Papilio, and the Odonata, have the wing muscles attached directly to the wings. One nerve impulse creates one wing-muscle con traction. The Ephemeroptera utilize this scheme. Their wings are constructed like corrugated sheets, which are very poor for a forward sculling action, but are admirably suited to the peculiar up and down flight they employ for the mating process. Since they do not feed while in the adult stage, they do not require effi cient forward flight. 3
The Hymenoptera and Diptera, and some Lepidoptera such as sphingid moths, must combine excellent flying ability with a small wing area. A hon eybee, for example, could not function well in its hive if it had large wings that were bulky even when folded over the back, as in Papilio or the Dobson fly. Bees compensate for a reduced wing area with a very rapid wingbeat. Wingbeat frequencies vary from 55 per second for some beetles, to more than 200 per second for the honeybee, and an incredible 1,046 per second for a midge. . . . Clearly, nerve tissue is not capable of firing this many times a second. These insects move their wings by an indirect, asynchronous muscle scheme. Opposing pairs of muscles act to depress and elevate the top of the thorax, to which the wing bases are attached. [The thorax is the middle section of the tripartite body of an insect.] With a portion of the thorax as fulcrum, the wings are levered up and down. A single motor nerve stimulus begins a cycle in which the contraction of one member of a muscle pair stretches the opposing muscle and stimulates it to contract. This process can be repeated several times before an other nerve stimulus becomes necessary to reinitiate the process, making possible high wingbeat frequencies. The natural elasticity of the thorax in the Diptera and some Coleoptera acts to enhance the activity by imparting a "click" action in which the wings are relaxed in the up and down positions. As they pass the center of the wingbeat pattern, they are driven swiftly to the extremes by this spring action.
The existence of such marvelous design corroborates the testimony of Scripture that God's eternal power and Godhead are revealed by the things that are made, so that man is without excuse if he rejects the truth. The existence of insect flight is a thorny problem for the evolution explanation of life. The fossil record helps very little, as the earliest [insect] fossil, believed to be of Devonian age, is a Collembolon, a wingless order well represented on the earth today; while the oldest fossils are fully winged, with no transitional forms.
Evolutionary theories
Alexander and Brown outline three principal theories for the origin of insect flight, then add a new one of their own.4 The first theory, the "flying fish" hypothesis, was developed by Oken.5 He believed that wings are homologues of nymphal gills of a primitive insect. Since abdominal gills are sometimes locomotory organs, it is postulated that these gills began to be used as gliding organs when insects leaped out of the water to escape predators. However, there are no gills on the back of the thorax in juveniles of modern insects, and tremendous difficulties are evident in transferring a juvenile apparatus constructed to function underwater to an adult device used for locomotion in the air. The flying fish analogy is not serviceable, because in sects are too small to break through the surface film in a similar fashion.
Forbes points to the fact that the back of the thorax projects laterally in crevice dwellers such as cockroaches, millipedes, and silverfish. 6 He believes that these projections could have been enlarged sufficiently to serve as gliding planes, affording a selective advantage in providing more effective dispersal and escape, and that muscles were introduced first to steer, and later to power, these appendages. A major problem with this hypothesis is explaining how such projections could afford a selective ad vantage before they were large enough to serve as gliding planes.
The third hypothesis introduced by Wigglesworth7 states that wings arose in tiny, passively airborne species to in crease buoyancy during wind-borne dispersal, muscles appearing later to provide control during takeoff and landing, and then flapping flight. An argument against this hypothesis is that small in sects such as aphids have such a small mass that active control of flight is virtually impossible. Drastic changes in structure would be necessary to make flapping, controlled flight a possibility. Also, it is not explained by this idea why wings are restricted to adult forms.
Alexander and Brown hypothesize in sect wings arose as mating display devices. 8 They mention among other things that wings of the flightless red katydid and many gryllids are used to generate sound, and also are lifted to expose tho racic glands from which the female feeds during copulation. They also point to the band-winged grasshoppers . . . which employ wing noises and display of brightly colored underwings as mating behavior. Wings would thus have originally arisen as mating display devices on the male, and later have evolved a flying function. They also point to Paleodictyopteran fossils, which have fleshy pronotal lobes in addition to large wings on the thorax. They believe that once the wings had evolved a locomotory function the function of mating display was taken over by the lobes. A problem with this hypothesis is explaining how the wings thus developed could be transferred to the female insect, and why the aforementioned tree katydids and gryl lids remain flightless if flight affords a selective advantage. Fossil evidence for the hypothesis is also lacking.
An engineering marvel
The presence of such differing theories of insect flight gives testimony to the fact that biologists are reluctant to leave any of the pages of the evolutionary scheme blank even when faced with meager and conflicting evidence. The fossil record lends so little support that entomologists are free to imagine any thing about the origin of insect flight. The fossil record, with its numerous examples of fully developed flying insects and lack of transitional forms, testifies that God created the living things to re produce their own kind. The engineering marvel of insect flight is one of God's many works that display His wisdom (Ps. 104:24).
Our understanding of God's role in Creation and especially His creation of us human beings is linked with our need of the gospel. Revelation 4:11 states that God is worthy to receive glory, honor, and power because He created all things and gives them their being. We are morally bound by God's creative ownership of us to bring Him glory and honor by obeying His law perfectly. In light of our rebellion against this imperative, how merciful it was of God to provide for our atonement (see Rom. 3:25) by the gift of His Son through whom He made the universe (see Heb. 1:2)! When we behold the marvel of insect flight we should rejoice that it displays God's handiwork and be humbly grateful that Christ the Creator (see Col. 1:16) stooped so low as to provide salvation for those men of His creation who will call on Him.
Notes:
1 G. R. Edmunds and J. R. Travers, "The Flight Mechanics and Evolution of the Wings of Ephemeroptera, With a Note on the Archetype Insect Wing," Journal of the Washington Academy of Science, 44:390-400 (1954).
2 William S. Romoser, The Science of Entomology (New Port, N.Y.: Macmillan Publishing Co., 1973).
3 Edmunds and Travers, op. cit.
4 R. D. Alexander and W. L. Brown, "Mating and the Origin of Insect Wings," Occasional Papers of the Museum of Zoology (Ann Arbor: University of Michigan, 1963), 628:1-19.
5 L. Oken, Lehrbuch der Naturphilosophie, ed. 2. (Jena: Fromann, 1831), cited by Alexander and Brown, op. cit., p. 3.
6 W. T. M. Forbes, "The Origin of Wings and Venational Types in Insects," American Midland Naturalist, 29:381-405 (1943).
7 V. B. Wigglesworth, "The Origin of Flight in Insects," Proceedings of the Royal Entomological Society, 28:6 (1963).
8 Alexander and Brown, op. cit.
Reprinted by permission of the Creation Research Society Quarterly, 16 (March, 1980): 195, 196.
