An insect uses its digestive system to extract nutrients and other substances from the food it consumes. Most of this food is ingested in the form of macromolecules and other complex substances which must be broken down by catabolic reactions into smaller molecules before being used by cells of the body for energy, growth, or reproduction. This break-down process is known as digestion. Insect blood or haemolymph's main function is that of transport and it bathes the insect's body organs. Making up usually less than 25% of an insect's body weight, it transports hormones, nutrients and wastes and has a role in, osmoregulation, temperature control, immunity, storage and skeletal function. The present book give descriptive material on morphological and taxonomical diversity of insects. A thorough knowledge on insects is provided by effective manner in this book. Hence, the book is useful guide to students and teachers in the field of entomology and environmental sciences.