by Philip S. Callahan INSECTS and How They Te IITPhilip S. INSECTS and How They Function With illustrations and photographs by the author As we become more aware of the impact of animals and plants on our lives, and of ‘our lives on theirs, the world of insects looms larger than ever. This book ex- plains how the organs and bodies of in- sects are built, how their marvelous struc- tures function, and how they sense the world they live in. The author describes the all-important integument, or “skin — a much more complex organ than one would imagine; how insects fly, and how they compare with man-made flying machines; their di- gestion and respiration; their sounds and sense of touch; their unusual eyes; their nervous and reproductive systems. In discussing communication, Dr, Cal- lahan dlescribes his widely accepted the- ory that the antennae of certain moths at least, and probably many other species of insects, sense odors by acting as electronic resonators that pick up the electromag- netic waves emitted by odor molecules— in effect, a biological form of man’s wave. guide antennas. To bring those interested in natural sci- ence closer to insects in a practical way, the author has included a number of in- teresting experiments that anyone can do with simple equipment. A Holiday House BookTn Philip S. Callahan INSECTS and How They Function with illustrations and photographs by the author HOLIDAY HOUSE - NEW YORKAcknowledgment hanks are due to Mi produced the t the U.S.D.A. R rch Laborat Carlysi ectron Printed in the United ISBN ¢ for WinnieContents The Living Insect ...... The Outside of Insects .. They Crawl and Creep . How Insects Fly ....- In Search of Food . The Unusual Blood ea Oxygen Spa se That Drowsy Hum How Insects Touch and Feel Things Seeing the World The Antennae and Insect Communication . . The Internal Switchboard Insects by the Millions .... Experiments with Insects Glossary Suggested Index .... 18 31 44 ST 72 79 89 O4 106 122 135 a. 154 -- 173 +. 181 « 185U. S. Department of Agriculture The coiled proboscis, or feeding tube, of the Indian meal moth, as seen. by the scanning electron microscope, Note the scales on the and part of the at left. Microscopes, icularly electron microscopes, show insects to be far cd in structure than most people imagine Chapter One The Living Insect Insects have a far greater effect on human life than is geherally realized. The very survival of the human race depends on our six-legged friends. This may sound like a contradiction, for in modern times the greatest emphasis has been placed on control of insect pests. Most insects, however, are beneficial; for instance, there are tens of thoutands of insects that prey on harmful species. As we trace the life processes of the insect let us keep in mind that they are far more important to men as allies than they are detrimental to his modern way of life. Insect physiology—the science of the life processes of insects—is very important to developing new methods of controlling insects that destroy man’s crops. The intensive cultivation of single crops in rows is favorable to huge build-ups of destructive populations of insects. The farmer sets the table, so to speak, for insect species that feed on the crop plants. Economic entomology, the science that develops insect controls, is one of the most important of all of our applied sciences; it prevents disease and social ills by assuring a wholesome and abundant food supply. To understand how it is related to the study of insect phys8 Insects and How They Function iology, we must find out the meaning of a third area of study, called ecology. Ecology is the science that explores the way plants and animals relate to each other in their particular surround- ings. We cannot understand the life processes of an insect unless we also understand how the insect fits into its en- vironment. The “inside” life processes of insects are di- rectly related to the “outside” forces around it. When man attempts to apply complicated control methods to his insect enemies, he must consider both these “inside” and “out- side™ factors, It is often stated in popular writings that both man and insects have been struggling to dominate the earth and that insects are giving man a good run for his money. The success of the cockroach is the example most often cited. The family of cockroaches, called’ Blatridae, is considered to have been in existence, essentially unchanged, for 250,- 000,000 years. Fossils differing little from the cockroach of today have been found in the rocks of the Upper Car- boniferous period of geological time. Although it is prob- ably true that man strives to dominate the earth, and we might now expand that to include the moon, certainly insects do not consciously strive toward such a goal. It is fortunate that they don’t, for they are so marvelously con- structed that they would overwhelm us in a short time. There are probably over 900,000 species of insects, grouped in 700 families; some entomologists estimate many more. Fewer than 1,000 of these species compete with mankind for food. Unthinking man, in his attempt to control harmful insects, often defeats his purpose by eliminating his insect friends. In order to prevent such insect tragedies the trained entomologist must have a ther- ough knowledge of both insect physiology and ecology. Corn earworm larva feeding on a tassel of corn. In early spring these larvae feed on the first ‘tassels as they emerge from the growing tip of the plant. Insect physiologists do not know why these young forms come in 50 many colors: yellow, green, pink, black, When we speak of insect control we immediately think of insecticides. This is unfortunate, for some of the most subtle insect-control methods have been based on a keen knowledge of insect physiology and ecology and not on the use of insecticides at all. The men who developed these methods have been in the forefront of the entomological sciences. They succeeded because they understood the physiology of the insect species they worked with. They were also able to define the ecological niche to which the insect was adapted by its physiology. “Niche” is the term used for the place in nature occupied by an organism. The niche of a corn earworm larva is the tip and silk channel of an ear of corn. The corn tip provides a home for it, and the temperature and humidity found in it are suitable to the bodily needs of the developing insect. It provides a microclimate, as the ecologist would term it, for the life processes, and also a source of food for the development and growth of the larva.10 Insects and How They Function INSECTS IN AGRICULTURE AND BIOLOGY The honeybee is man’s most useful insect ally. We usually think of bees as the producers of honey and beeswax. However, the fifty million dollars’ worth of honey and beeswax produced in the United States is insignificant alongside the one billion dollars’ worth of agricultural crops that they pollinate. If it were not for the honeyhee, many crops could not be grown at all. Agricultural scientists estimate that this insect is responsible for 80 per cent of all crops pollinated by insects, Crops that depend on bees for pollination include alfalfa, clovers, apples, apricots, cran- berries, citrus, cantaloupe, watermelon, peaches, plums, almond nuts, asparagus, broccoli, cabbage, celery, lima beans, artichokes, cotton, and a host of other crops. An impressive list indeed, When we think of physiology, we usually think of the life processes of a single organism, but in the case of social insects like bees and ants we must expand our definition to include an entire society of insects. Maurice Maeterlinck, the Belgian writer and literary Nobel Prize winner, in his delightful classic, The Life of the Bee, treats the entire beehive as a living organism. For him the bee society is an incredible and complex living organism with each type of bee, queen, drone, and worker, functioning through spe- cialized physiological division of labor as parts of the whole. ‘William Morton Wheeler, the great Harvard ant behavior- ist, used a similar analogy to compare an ant colony to a cellular organism. Eugene N. Marais, writing about ter- mites, philosophizes on the strange force that holds the colony together and calls it The Soul of the White Ant— an appropriate title for his book. The Living Insect 1 Modern entomologists know that the colonies are held together by complex chemical messengers that control the chemical messengers pheromones from the Greek pherein (“to carry”) and horman (“to excite”). These pheromones could be compared to external hormones for, like hormones, which carry messages between the cells within an organism, pheromones function externally to carry messages between individuals. To understand the physiology of the bee, the ant, or the termite we must study not only the individual but the entire colony as well. The value of honey as food has long been known to man; drawings in a Paleolithic cave at Arana in Spain depict prehistoric man collecting wild bee honey. Besides insect products, however, insects themselves are a source of food. ‘We know that many species of birds and certain mam- malian insectivores, or insect-eaters, could not continue to survive without insect prey. The consumption of insects, called entomophagy, was also one of man’s early habits. Most people in modern civilizations do not consider insects as eatable. We are limited by our refinement of food habits, which is based on modern agricultural practices. The fact remains, however, that a good portion of the human population could not survive in a healthy state without insects as food. Scientists who study primitive tribes are aware that their usual diets are often deficient in animal fats and protein, and yet the people appear healthy. This is because insects are a regular part of their diet. An analysis of grilled termites, for instance, shows them to contain 36.2 per cent fat, 45.6 per cent protein, and 5 per cent ash, and to equal 508 calories per 100 grams of weight. These insects are an excellent protein source for human consumption.12 Insects and How They Function I can vouch personally for the value of boiled wood- boring beetle larvae as food. I lived on them for five days while hiking through the jungles of Samar. I learned about eating insects from the Negritos, Pygmy-like people of Luzon in the Philippines. Eugene Fischer, an anthro- pologist, studied the Pygmies of the African rain forest and found that insects formed an indispensable part of their diet, With the world population expanding at such a tre- mendous rate there is no valid reason why certain insects species should not actually be cultivated for human food. We may discover that certain high-protein species are physiologically suited to mass rearing for this use. We could then have, besides an animal husbandry, a food science called insect husbandry. Insect predators have been used to control destructive insects. Insects are also useful in the control of weeds. Klamath weed was introduced into the United States from Europe about 1900. It completely overcomes the land, killing all other plants except larger shrubs and trees, It is also poisonous to livestock. A leaf beetle, Chrysolina gem- elata, was introduced from France and rapidly cleared more than 100,000 acres of weed in California. It also reduced the pest weed in Washington, Oregon, and Idaho. A knowledge of the biology and physiology of insect species is vital to control of destructive species, Certain insecticides do not break down chemically at a rapid rate and thus they build to high concentrations and pollute the environment, Often insecticides that do break down in the soil cannot be used on certain crops for economic reasons. A farmer could not afford to spray vast acres of wheat for an insect such as the Hessian fly. The Living Insect 1B This fly was named after Hessian mercenaries by the Americans during the Revolutionary War. It was thought to have been introduced on Long Island, New York, near Lord Howe's encampment, in the bedding straw of his soldiers. After 1779 it spread west with the frontiers. It became the most injurious insect enemy of the winter wheat in the Midwest. The entire fall generation of the midgelike fly emerges as adults within a short period after the late summer rains. Entomologists found that if farmers planted wheat after this period no eggs would be laid on the sprouting wheat. They therefore set planting dates, dependent on latitude, to allow plants enough good weather to mature before winter, but late enough to avoid the emergence of the Hessian fly. In Northern Arkansas, for instance, a farmer would be advised to plant after October 16. In northern Illinois, where winter comes earlier, the date of sowing wheat is a month earlier, around September 20. This is an excellent example of how the insect ecologist with a knowledge of the temperature needs of an insect can turn the environment to good use. No insecticides are necessary. Entomologists have been turning out successful controls like this for generations. THE USES OF DROSOPHILA There are two species that lead all others in their use for physiological experimenting. They are the honeybee and the well-known fruit fly, Drosophila melanogaster. Genetic studies have stimulated a vast amount of phys- iological experimentation on the fruit fly. It is the guinea pig of the insect world and its contributions to medicine14 Insects and How They Function and biology are unequaled by any other insect speci m the alimentary canal of Tumors have been isolated fr Drosophila. These tumors were found to be genetically controlled, although some environmental factor may also be involved. Such insects are ideally suited for genetic and medical research. Insect species are utilized for research because they are usually «7 to rear and handle, require little laboratory id most important of all, pass through many gen- ns in a short period of time. Because they can be erat easily reared in large numbers the are often used to study biological rhythms. Accurate data require large popula ch studies. The literature on insect physiology describes many temperature and radiation: tions of test organisms for = experiments directed at solving the secrets of insect rhythms THE AESTHETIC VALUE OF INSECTS Even if the study of insect p! ‘were not important to the re and bi Id still attract erested researchers, We cannot look fields of agricult a great number of in ing electron micro at the sed ‘ope photo of the imported ot wonder how such z eant and range animal func When one steps on an ant he most certainly crushes a marvelous piece of biological engineering We look in amazement at the legs and antennae, the compound eye, the mandibl Even the least cur evolved. The world of insects is a wonderful world and even the youngest among us soon become aware that ther parts. wus might ask how such a creature s, the thorax, and Insect parts are often beautiful in form and texture, as this electron-microscope picture shows. The organs in many cases are highly varied from species to species. This fire ant worker, for instance, has far fewer facets in its compound eyes than certain moths and dragonflies, which may have 20,000 to 30,000. Note the structure of its antennae; some moths, by contrast, have an- tennae shaped like feathers or leaves, The posterior end of this ant is illustrated in Chapter 3 it is a different world. It is almost as if creatures from an- other planet existed right in our own backyard, available to study. Many insects are not only useful, but because of their coloration also esthetically pleasing. Volumes could be filled with the lines that poets have written to butterflies16 Insects and How They Function There is a Japanese haiku (a short 17-syllable verse) that says “What a delightful game it is to set / Fireflies loose in a bed beneath the net!" The bed net of course is to keep the mosquitos out, but on summer evenings Japanese chil- dren collect fireflies and let them loose under the nets. The artistic genius of the Japanese is for perfection in small things. That genius is demonstrated in their love of insects. It is one of the few lands in the world where a child gains enjoyment from a cricket in a cage. Japanese cricket cages are works of art built of fine bars of split bamboo. Every year in August at the Chinzan-so palace grounds in Tokyo there is a cricket singing contest. Children from all over Tokyo bring their caged crickets and the night is filled with cricket music, The recording and analysis of such insect sounds and of insect hearing is an important part of the study of insect physiology. A Japanese boy in Kamakura catches a cicada in his insect net. Insects are popular pets in Japan. The Living Insect 17 Just as interesting as the shape, the color, and the sounds of insects are their habits. One of the fathers of early American entomology was John Henry Comstock, professor of entomology at Cornell University. His book An Introduction to Entomology is a fascinating excursion through this far-out world. I often use his books to learn about the habits of insects that I observe in the woods and fields. For example, one day while I was hiking along the Appalachian Trail I saw white spots dancing up and down along the pathway; they looked like small silver balloons bobbing a few feet above the littered forest floor. At first I thought they were sparkles of dew caught on cobwebs. I reached for one and it evaporated in my hand. On close examination I found they were male flies, each of which carried a small inflated shining air sac. These delicate little balloons are produced by the male during the mating flights, which take place early in the morning. The female is attracted to the dancing balloons; it is the visual communication signal of the mating flight. Think of the complex physiological processes within the male to produce this signal! It is one of the marvels of the insect world that is not to be forgotten once it is observed. When I arrived home I found a description of these early- morning creatures in Comstock’s book. They are called dance flies, Perhaps when we have learned more of insect physiology from the following chapters we will better appreciate the marvels of the insect world, Besides the practical benefits of such study to agriculture and biology, perhaps a better acquaintance with the way insects function will give us a deeper appreciation of these animals in our everyday lives.