WHAT IS AN INSECT?

WHAT IS AN INSECT? With over 4 million of them on each acre of the earth, it is surprising that few of us actually know what insects really are. For some reason, we want to place every little creature in this tremendous class particularly if it is a pesky, creepy-crawly one. Spiders, centipedes, mites, millipedes, scorpions, ticks, and harvestmen are continually mistaken for insects when they are actually no more closely related to insects than lobsters or mollusks are. What then is an insect? Basically, insects are small backboneless animals (invertebrates). They share certain physical characteristics that, together, distinguish them from all other animals. Three body segments. Insects are usually elongate in form with three distinct sections of the body: head, thorax, and abdomen. The main sensing organs eyes, antennae, and mouthparts are on the head. The thorax bears wings and legs, and the abdomen has most of the digestive and reproductive organs as well as breathing holes called spiracles. Outer skeleton. The body parts are sometimes difficult to detect since the insect's entire body is covered with a coat of armor. Instead of a backbone and skeleton as we know it, insects possess a hard, jointed frame on the outside of their body. This exoskeleton is made of chemical substances and proteins secreted by the insect’s body. it is braced and ridged at various points to provide support as well as protection. Insoluble in water, alcohol, and most acids and enzymes, it provides a barrier to the world. It also makes the insect’s body a rather clumsy package at times. Movement is difficult and growth can occur only when the exoskeleton is popped open during molts. Six jointed legs. All insects have three pairs of legs attached to the thorax. This number gives the animal greater balance and mobility than any other. In walking, the insect moves the middle leg on one side of the body, together with the front and hind legs on the opposite side. This leaves three legs forming a stable tripod on the ground. _ In addition to six legs, caterpillars have up to five pairs of plump, fleshy false legs that enable them to move more easily. These prolegs are hooked so that the larva can hang effortlessly from the host plant. Sawflies also have prolegs. Two or four wings. Although many insects are wingless at some point in their lives, most adults possess one or two pairs of wings. The wings are actually part of the body wall. They begin as soft saclike outgrowths and later flatten and dry into solid membranous structures. They are supported by a framework of tubes and connected to the thorax by a series of muscles. These four basic characteristics help to formally classify insects within the Animal Kingdom. Scientists group animals into major divisions on the basis of structure. The largest divisions are phyla which are subdivided into classes. Insects make up the class lnsecta or Hexapoda (meaning six legged) of the phylum Arthropoda (meaning joint legged). Any animal with six jointed legs is an insect. Mites and spiders have jointed legs but they have eight, not six, of them. Hence, they belong to a different class in the phylum Arthropoda. The Insect class is further divided into 26 orders. Orders are large groups of insects that share similar wing structures. Members of the order Coleoptera (beetles), for instance, are distinguished by a front pair of leathery or brittle wmgs that meet in a straight line down the center of the back. Insects belongmg to the order Hemiptera (true bugs) possess front wings that are partly thickened and partly membranous. The order name appears beneath each chapter head. 1 Each order contains one or more families. The family name always ends in idae and refers to some particular feature its members share. Beetles belong~ ing to the family Buprestidae are hard-bodied, brightly colored, metallic insects. In the larval stage, they have a flatheaded appearance and are known as the flatheaded wood borers. Members may look exactly alike or they may resemble one another only slightly, but all have a flat head.

The most fundamental levels of classification and the ones that are most used to identify insects are the genus and species. The genus name refers to a small group of closely related members of a family. It is always capitalized. The species name is seldom capitalized. It refers to a single insect that can be distinguished from others in the genus by a particular feature or habit. Thus, both the asparagus beetle and the spotted asparagus beetle belong to the genus Crioceris but, since their markings and their habits are slightly different, they are distinguished by separate species names: asparagi and duodecimpunctata. These, together with the genus name, are the insects’ formal names. In this handbook, they appear just below the common name at the top of each insect entry.