Insects by Simon Leather

Author:Simon Leather [Leather, Simon]
Language: eng
Format: epub
ISBN: 9780192586322
Publisher: OUP Oxford
Published: 2022-04-12T00:00:00+00:00

In Chapter 5 we leave the terrestrial habitat to explore the adaptations and lifestyles of insects that spend some or all of their life in or on water.

Chapter 5

Aquatic insects

Aquatic insects, adaptations, the marine environment

Although largely terrestrial, insects have not abandoned the world of water. Every inland water body, whether a river, stream seepage, or lake, supports a biological community. Insects can also be found in puddles and some, such as the pitcher plant mosquito, Wyeomyia smithii, are especially adapted to exploit the water-filled ‘stomachs’ of carnivorous plants. In larger water bodies, the most familiar inhabitants are often the vertebrates, such as fish and amphibians. At the macroscopic level, however, 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 them in terms of species numbers, biomass, and productivity. Crustaceans may be abundant in saline (especially temporary) inland waters but are rarely diverse in species. Some representatives of nearly all the orders of insects live in water and there have been many invasions of freshwater from the land. Recent studies have even revealed a diversity of aquatic diving beetles (Dytiscidae) in aquifers (underground water bodies). Insects, however, have been almost completely unsuccessful in marine environments, with a few sporadic exceptions such as some water-striders (Hemiptera: Gerridae) and larval dipterans.

There is little doubt that insects evolved on land, albeit from an aquatic crustacean ancestor (Chapter 1). The tracheal system of respiration, based on diffusion, is very unlikely to have evolved in water; oxygen levels are much lower in water than in air, reaching only 15 parts per million (ppm) even in flowing water. It is much more plausible that the tracheal system facilitated the subsequent development of the ‘gills’ used by insects that are truly aquatic for part or all of their lifecycles.

Many insects have aquatic larvae, such as dragonflies, mayflies, and several species of fly, including mosquitoes. There are also some adult forms, mainly predators, that make a living in these environments, either below the surface or striding or skating across the surface. Insects that live on the surface of the water—water boatmen and pond skaters—rely on the fact that their light weight and limited contact with the water surface keeps them high and dry. Insects that feed in water but are otherwise terrestrial have special adaptations that allow them to spend prolonged periods of time underwater. Adult diving beetles store air underneath their wing cases while other semi-aquatic insects encase themselves in a bubble of air, which they refresh as needed by returning to the surface.

Insects that are truly aquatic have developed gill-like structures—fine filamentous, thin-skinned outgrowths that are able to absorb oxygen through diffusion. They depend, however, on being in a well-aerated water body or having the ability to generate a flow of fresh water over their gills, as seen in some of the ‘sedentary’ caddisflies that live in a ‘burrow’ and use their legs to produce an artificial current.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.