SOME BRIEF FACTS... Freshwater insects (otherwise known as 'aquatic macroinvertebrates') are found in almost every body of freshwater around the world. Most are simply the juvenile life stage of terrestrial flying insects (such as aquatic mosquito larvae or "wrigglers" and their flying terrestrial adults). Apart from their importance in the ecosystem's concerned food web, where they are a vital link making lower level energy sources such as algae and detritus available to higher levels such as fishes, they also provide us with an idea of the water and habitat quality of the water body. By definition, "pollution" is a impact that kills life within the system in which it is received; clearly therefore the best place to look for a impact then is at the level of the organisms themselves! Therefore, by looking at the macroinvertebrate community of the stream or lake etc. (that is insects, plus snails, worms etc.) we can develop an idea of the water quality of the system based upon what is present, and what is not.

This is because the pollution sensitivity of different macroinvertebrate groups varies predictably as follows...

Aoteapsyche colonica	Zephlebia sp.	Stenoperlus sp.
FROM PENDERGRAST & COWLEY (1966).

The following are not insects, but are also commonly used as indicators of water quality also...

For a summary of this system of subscribing water quality values based on the insect species present click here...

WHAT THEIR PRESENCE/ ABSENCE THEN MEANS... An absence of "sensitive" species such as mayflies may imply that the site is degraded. This is even more likely if the only species that are present are the pollution tolerant ones e.g. oligochaete worms. However; the absence of the sensitive species may either be due to the presence of a pollutant or general water and habitat quality. Therefore, noting water temperature, degree of siltation, testing for specific pollutants, etc. and finally the observer's experience all play further important roles in the final analysis. These factors will also all consequently figure in the decision-making process when methods and options for rehabilitation are being determined.