10. Aquatic insects
Every inland waterbody, whether a river, stream, seepage, or lake, supports a biological community. The most familiar components often are the vertebrates, such as fish and amphibians. However, at least at the macroscopic level, invertebrates provide the highest number of individuals and species, and the highest levels of biomass and production. In general, the insects dominate freshwater aquatic systems, where only nematodes can approach the insects in terms of species numbers, biomass, and productivity. Crustaceans may be abundant, but are rarely diverse in species, in saline (especially temporary) inland waters. Some representatives of nearly all orders of insects live in water, and there have been many invasions of freshwater from the land. Insects have been almost completely unsuccessful in marine environments, with a few sporadic exceptions such as some water-striders (Hemiptera: Gerridae) and larval dipterans.
This chapter surveys the successful insects of aquatic environments and considers the variety of mechanisms they use to obtain scarce oxygen from the water. Some of their morphological and behavioral modifications to life in water are described, including how they resist water movement, and a classification based on feeding groups is presented. The use of aquatic insects in biological monitoring of water quality is reviewed and the few insects of the marine and intertidal zones are discussed. Taxonomic boxes summarize information on mayflies (Ephemeroptera), dragonflies and dam-selflies (Odonata), stoneflies (Plecoptera), caddisflies (Trichoptera), and other orders of importance in aquatic ecosystems.