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Introduction As humans, we tend to categorize objects and ideas into logical groups. Classification schemes can be based on use, size, color, shape, or a myriad of other methods. In my workshop, I have an area where I store various fasteners. In one bin, I have nails; in another, screws; and in still another, bolts. Even within these groups, I have additional divisions . I have separate bins for different types and sizes of bolts, such as F-inch hex bolts, A-inch carriage bolts, and so forth. Grouping similar objects enables us to find a particular item of interest quickly and efficiently. Entomologists disagree about the number of insect species currently living on earth; nevertheless, with estimates ranging from 2 million to 30 million species, it is fair to say we personally can be familiar with only a very, very small number of insects. However, in many cases we can recognize groups of insects with morphological, biological, and ecological similarities. Systematics, the study of the diversity of living organisms and the relationships between them, is a cornerstone of biology. Taxonomy, the science of describing , classifying, and naming organisms , is a subdiscipline of systematics that attempts to group living things into a logical scheme. Taxonomy is not a new concept. In Genesis 2:19–20, the first book of the Bible, God allowed Adam to name all the living creatures on earth. In the fourth century b.c., Aristotle developed the first known scientific classification system. Carl Linnaeus, an eighteenth-century Swedish botanist, laid the foundation for the taxonomic system we now use. This system groups organisms according to their similarities from broadly similar to very similar. A simplified hierarchical system (from broad to specific) commonly used today is similar to the following : Kingdom (broadest grouping) Phylum Class Order Family Genus Species (most specific   grouping) The fundamental unit of this system is the species, which may be defined as a group of organisms that are very similar in appearance, physiology, genetics, and ecology. Each species is assigned to a broader group called a genus that is composed of similar species. The members of a genus are grouped with other similar genera to form a broadly related family and so forth. To help you recognize group levels, this book uses color to distinguish families, orders, and classes. The above depiction of the hierarchical classification system is simplified. There are typically subdivisions at each rank; for example, Kattes_book.indb 1 2/13/09 7:02:51 AM 2 introduction in some cases, there may be superfamily, family, and subfamily groups. Taxonomy is not static. As scientists learn more about an organism or group of organisms, the taxonomy is changed to reflect this new knowledge. A species may be reclassified in a different genus. What were originally believed to be two or more species may actually be the same, with the apparent differences due to geographic or other forms of iso­ lation. Data interpretation by various scientists may also influence the classification system. Some taxonomists, known as “splitters,” separate groups based on several observed differences. Taxonomic “lumpers,” however, may view these same differences as less important than some overriding major characteristic and thus have fewer groups. What Is an Insect? Insects are members of the kingdom Animal and phylum Arthropoda. Arthropods have a hardened shell called an exoskeleton, paired jointed appendages that include legs, fingerlike projections near the mouth called pedipalps, antennae, and other structures. These typically small animals are bilaterally symmetrical; if you were to draw a line down the middle of the organism, appendages on both sides of the line would be identical. The phylum Arthropoda is divided into five classes: (1) Arachnida (spiders, scorpions, and others); (2) Crustacea (sowbugs, crayfish, and others); (3) Diplopoda (millipedes); (4) Chilopoda (centipedes); and (5) Hexapoda (insects). The hexapods are generally easily separated from the other classes by having three body segments , six legs, and one pair of antennae ; they are the only class that may possess wings. Internally, insects have a tubular gut with a mouth and an anus. Their nervous system consists of a brain located in the upper portion of the head. The brain is connected to a nerve cord located on the ventral, or underside, of the organism below the gut. Insects have an open circulatory system . Rather than being pumped through veins and arteries by the heart, arthropod blood—hemolymph—flows through openings in the heart located on the dorsal, or upper side, above the gut. The fluid bathes the internal...


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