Identifying Water Quality with 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.
Magazine Articles Science

Testing pollution levels in natural water bodies can require a considerable amount of gear and instrumentation. However, there is another much simpler solution. Observing the species of insects that live in natural water bodies and identifying them can reveal how polluted that particular water body is. This method of observing pollution in natural water bodies is called bio-monitoring and the particular insect species that help us in determining the approximate pollution levels are called bioindicators.

Insects are an intrinsic part of aquatic environments, and there is an incredible diversity of insect species that can be found in natural water bodies around the world, although the types of species found can be regional and site-specific. Certain insect species can be found in even the most polluted habitats that can be found. For example, John Roach in National Geographic reports that the streams flowing into the Carson river in Nevada and northern California run below an abandoned sulphur mine located in the Sierra Nevada mountain range. Laced with toxic acids and heavy metals, although the US Environmental Protection Agency (EPA) had declared the sites as among the most polluted sites in the US in 2000, studies looking for the possibilities for the restoration of these ecosystems looked towards primarily studying the possibility for certain species of tolerant insects to survive in these environments after clean ups were initiated (J. Roach, 2007).

Needless to say, although most aquatic life would be less resistant to polluted environments including many insect species, whose absence can also be noted, many species of insects can be much more resistant in environments with increased or increasing pollution levels. This quality allows for the species composition of insects in aquatic ecosystems to act as bioindicators to help us in determining an approximate measure of pollution levels in natural water bodies. This can also serve as a barometer to guide the use of instrumentation to check pollution levels in water bodies in case the infrastructure is lacking for example in the case of underdeveloped regions or if one would need to check by oneself for pollution levels in minor water bodies that have not been adequately covered by instrumentation.

A Useful Tool for Indian Observers

Water quality in India has been under the scanner for a considerable amount of 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 Trend). 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 a 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, are sedentary, and easy to sample, these organisms serve as a viable indicator. 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.

Testing Water Pollution in India

Impure water or water pollution can in the most basic instance cause health effects on humans such as effects on the mucous membrane, lead to gastro-intestinal irritation, dental and skeletal fluorosis, methaemoglobinemia, etc. The effects are multiplied when the water is polluted and filled with toxins, which can cause many water-borne diseases. Pollutants can also bio-accumulate in the food chain and have multiplied effects.

When instrumentation is used to check water quality in India, institutions measure the contaminants in water in terms of quantitative concentration depending on the characteristics of use of the water. Thus depending on how water is to be used, it is deemed on the basis of various parameters how objectionable the particular sample of water is. In case of unusually high concentrations of toxins, the water is declared unusable, and this depends upon the parameters utilized by the analyst. Various guidelines are available in India to determine water quality such as the Bureau of Indian Standards – BIS standards, the Central Pollution Control Board (CPCB) standards, etc (L. Deshpande, undated).

An innumerable number of toxins can be present, including arsenic, nitrates, lead, sulphates, fluorides, and even salt for instance can be detrimental to agricultural productivity. Tests for these toxins mostly involve laboratory tests for the given chemicals. Many methods and techniques are involved in this such as noting the water temperature, pH tests, measuring the dissolved oxygen, measuring nutrients and toxins (D. Hadley, 2017), membrane filter tests, multiple tube dilution tests, etc (L. Deshpande, undated). Most of these laboratory methods however, are costly and time consuming, and bio-monitoring represents a cost-effective and quick method of if not investigating the exact nature of pollution, of acting as a warning system for pollution watchers to investigate and report.



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.



Deshpande, L. Undated. Water Quality Analysis: Laboratory Methods. National Environmental Engineering Research Institute (NEERI), Nagpur. Council of Scientific & Industrial Research, New Delhi, Government of India.

Hadley, D. 2017. What Aquatic Insects tell us about Water Quality. Thought Co. October 16, 2017.

Roach, J. 2007. Insects Key Indicators of Water Health, Experts say. National Geographic News, February 1, 2007.

Leave a Reply

Your email address will not be published. Required fields are marked *