Learn it from the insects

By: Staff Reporter
The essay urges you to develop skills in recognising organisms whose survival is intrinsically linked to the quality of water. Conversely you can gauge the quality of the surface water through a cursory inspection.

Article 9 Figure 1Water quality in India has been under the scanner for considerable time now. Chemical testing falling within the scientific purview, uses instrumentation to publish results at periodic intervals, identifying pathogens and other inorganic toxic substances in the water. But then, say one was to identify by mere observation how clean a water body is— would that be a possibility or do we need Superman’s x-ray vision? For such curious individuals biomonitoring is the answer. Here is a brief backgrounder to whet your learning appetite and hone your skills to thrill your friends and family.

Biomonitoring is generally defined as “The systematic use of living organisms or their responses to determine the condition or changes of the environment” (Zheng, Binghui, et al., (2010), ‘Biomonitoring and Bioindicators Used for River Ecosystems: Definitions, Approaches and Trends). A study by K A Subramaniam, Center for Ecological Studies, Indian Institute of Science, Bengaluru, in 2003 of the riverine ecosystem in the Western Ghats concluded that Baetidae (order Ephemeroptera) (mayfly), Libellulidae (dragonfly), Psephenidae (water-penny bettles), Dytiscidae (diving beetles), Hydrosychidae (net-spinning caddisflies) and Simulidae (black fly) are species that are resistant to pollution, hence are more commonly found in river patches that have been heavily degraded. Although many biological organisms can be used to monitor water quality, such as fishes, macrophytes, algae, and macro-invertebrates, but with the exception of the latter, all have inherent drawbacks.

Macro-invertebrates are aquatic macro fauna lacking vertebral column, dependent on the bottom of water bodies—freshwater, estuarine or marine, at some stage of their life cycle and living attached to rocks or plants. As they are visible to the naked eye, have a long life span, sedentary, and easy to sample, these organisms serve as viable indictor. Macro-invertebrates are intimately related with the environment and any alterations produced in the physical and chemical status of an aquatic ecosystem becomes recognizable through the community structure of the organisms. In fact the presence or absence of certain species or of their associations can give a fairly accurate estimation of the degree of pollution present.

Insects generally dominate macro-invertebrates. The orders Ephemeroptera (mayfly), Plecoptera (stonefly), Trichoptera (caddisfly), Diptera (true fly) and Odonata (dragonfly and damselfly) make up the majority of these indicators. The other important groups in freshwater are the Planaria (flatworms), Mollusca (shells and clams), the Annelida (worms and leeches) and the Crustacea (crayfish, water lice, crabs).

Table 1 holds a brief description of the creatures that mark pollution levels. These aquatic insects may be commonly found in streams and water bodies. Some critters can survive in nasty polluted water while others may die with even a little toxicity.


Despite its fairly well-documented taxa, we need more studies on biomonitoring in aquatic ecosystems to create a baseline of information in an easily accessible format or database in India. This would come as a tremendous aid to communities by providing them the power to determine the quality of surface water and assist in the redemption of water bodies without the need of expensive instrumentation.

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