Insect body structure and the aquatic insect orders

Abstract

Statistically, most animals are insects, i.e., more than half the animals alive at any one time are insects. The aquatic insects, however, do not form a distinct taxonomic group. Some orders contain only species that are aquatic in some life stage, but other orders contain both aquatic and terrestrial species. Insects evolved on land and aquatic insects are essentially terrestrial insects that have found a way to live underwater. Consequently, aquatic insects are enormously variable in morphology, development, physiology, and ecology. The diversity of ways in which insects have evolved an aquatic existence at some point in their life-cycles is enormous. Nonetheless, many features of morphology and life-cycles are common to all insects. All insects follow the same basic body plan and some understanding of the basic body structure is essential to any treatise on aquatic insects. Entomology is rife with subject-specific terminology to describe different body parts and, although this can be frustrating, this vocabulary is necessary. This chapter provides a brief description of the types of life cycles of insects and then explains the external morphology of insects, followed by descriptions of the insect orders that contain species that are wholly or partially aquatic.