Insects are a remarkable group of animals. They occur almost everywhere and make up more than half of all the living things on this planet, they play a significant role in the world of nature and affect man directly or indirectly in many ways, and (they exhibit some unusual physiological and structural peculiarities.

There are several hundred thousand different kinds of insects (about 88,600 in the area covered by this book), and they occur in almost every type of habitat. The only habitat they have not invaded to any extent is the ocean. Most of them are small, and some are minute. Our species vary in length from less than a millimeter to about 6 inches, but more than half of them are less than inch long. This means that they can live in small situations, and a small but diversified area may contain many kinds — there may be more kinds of insects on an acre than species of birds in the entire United States, and their numbers may be as high as several million per acre.

From man's point of view the insects are extremely important animals; some are very destructive, and many are very beneficial. Insects may damage or kill cultivated plants, they may damage or contaminate stored foods and other products, and they may attack man or animals and bite, sting, or act as vectors of disease. Annual losses caused by insects in the United States have been estimated to be about $3 y2 billion. On the other hand, insects do a great deal of good. Many are important agents in the pollination of plants, including most orchard trees and many vegetables and field crops; some provide products of commercial value (honey, beeswax, silk, and shellac); many are important items in the food of birds, fish, and other animals; those parasitic or predaceous on other insects help keep noxious species under control; many are valuable scavengers'; some have been used in the treatment of disease; many have been used in studies of heredity, evolution, stream pollution, and other biological problems; and insects are interesting and often very beautiful animals. Most people look upon insects as undesirable pests, but we believe insects do more good than harm: insects' pollinating services alone are probably worth about $43^ billion annually in this country.

Most insects have an enormous reproductive capacity, and if it were not for the many checks on their increase (enemies, adverse environmental conditions, and the like) we would soon be overrun by them. To cite an extreme example: a pair of pomace flies (Drosophila), in which the female can lay a hundred eggs, may have 25 generations a year and could (if there were no checks) increase in a year to about 1041 flies. This number of flies, packed a thousand to the cubic inch, would form a ball 96 million miles in diameter] Many insects can reproduce parthenogenetically (without a male fertilizing the eggs), and the eggs of some insects hatch into not just one young but into many — over a thousand in the case of some of the chalcids.

We are concerned in this book primarily with the problem of identification, which is a first step in getting acquainted with any group of animals, but we have included some information on the structure, habits, and importance of the various insect groups. We hope that those beginning the study of insects with this Field Guide will go beyond identification to further study of these animals.

We have been aided in the preparation of this book by a great many people. Some have read portions of the manuscript and have made helpful suggestions and criticisms, and others have provided information on specific points. Various specialists, particularly in the combined United States Department of Agriculture and Smithsonian staffs of the United States National Museum, have assisted by loaning specimens used in preparing the color plates and many of the drawings. We are particularly indebted to Donald M. Anderson, Barnard D. Burks, Kellie Burks, George W. Byers, Oscar L. Cartwright, Arthur D. Cushman, Donald R. Davis, W. Donald Duckworth, J. Gordon Edwards, William D. Field, Oliver S. Flint, Richard H. Foote, Paul H. Freytag, Richard C. Froeschner, Raymond J. Gagné, Ashley B. Gurney, Jon L. Herring, Ronald W. Hodges, John M. Kingsolver, Josef N. Knull, James P. Kramer, Karl V. Krombein, John D. Lattin, Paul M. Marsh, Frank W. Mead, Frank J. Moore, C. F. W. Muesebeck, Lois B. O'Brien, André D. Pizzini, Louise M. Russell, Curtis Sabrosky, David R. Smith, Thomas E. Snyder, Paul J. Spangler, Ted J. Spilman, George C. Steyskal, Alan Stone, Eileen R. Van Tassell, Edward Todd, Charles A. Triplehorn, George B. Vogt, Luella M. Walkley, Rose Ella Warner, Donald M. Weisman, Janice White, Willis W. Wirth, and David A. Young. We wish to thank those on the staff of Houghton Mifflin Company whose expert advice and assistance have made the production of this book possible.

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