1. How Canaries Helped Keep Coal Miners Safe from Toxic Gases
In the past, coal mines in Britain faced frequent accidents caused by toxic gases that humans could not see. After a major explosion in 1896, a British scientist named John Scott Haldane suggested bringing birds into the mines. [1]
The bird chosen for this job was the canary. Canaries have a more sensitive respiratory system than humans, so they are affected by toxic gases much faster. [1] [7]
Miners watched their canaries closely. If the bird stopped singing or fell off its perch, the miners knew danger was near and could escape. This method was used for a long time. However, in December 1986, Britain officially stopped using canaries in coal mines. [1]
Safety Note: In the past, miners relied on the bird's distress signals to evacuate. Today, when exploring nature, always do so with an adult and be careful of slippery surfaces.
2. Why Some Living Things Can Be Used to Measure Environments
Just like the canary, some living things are very sensitive to changes in their surroundings. Others can only survive in specific conditions. Scientists call these creatures "indicator species." [2]
By checking if an indicator species is present, or if there are many or few of them, we can get a rough idea of the environment's condition without using complex machines. [2]
In this way, the living creature itself acts as a "living ruler" or measuring stick for the environment.
3. How River Bugs Show Water Quality in Japan's National Survey
In Japan, the Ministry of the Environment and the Ministry of Land, Infrastructure, Transport and Tourism have conducted the "National Aquatic Organism Survey" since 1984. [4]
In this survey, participants turn over stones at the bottom of a river. They identify the types of insects found under the stones. Based on these insects, the water quality is divided into four classes. [3]
Clean water is home to stoneflies and flat-headed mayflies. Slightly polluted water hosts small caddisflies. More polluted water is where water mantises and giant water bugs live. Very polluted water is typically inhabited by midge larvae. [3]
A great feature of this survey is that anyone can join, including elementary and middle school students, without needing to be a specialist. In the 2024 fiscal year, approximately 38,000 people participated across the country. [4]
4. How Daphnia Are Used to Test Chemicals in the Laboratory
Indicator species are not just used to check the current state of rivers or seas. They are also used to test how toxic new chemicals might be before they are widely used. A prime example is the daphnia, a tiny water flea. [5]
In 1984, the OECD (Organisation for Economic Co-operation and Development) adopted a standard test method called the "Daphnia Acute Immobilisation Test." [5] In this test, newly hatched daphnia are exposed to chemicals at various concentrations. Scientists then count how many of them become unable to swim.
In 2004, the duration of this test was extended from 24 hours to 48 hours. [5]
Daphnia are chosen for these tests because their bodies are small and transparent, making them easy to observe. They also reproduce quickly and react sensitively to even small amounts of chemicals. [6]
5. The Strengths and Limits of Using Indicator Species
Surveys using indicator species have a strong advantage: many people can participate immediately to understand their environment without specialized machines. The experience of entering a river to observe living things has great value in itself.
However, there are limits. The aquatic organism survey reveals general trends in water cleanliness, but it does not show exactly which chemicals are present or in what quantities. Results can also change depending on the season, the location, or the person doing the survey.
Therefore, simple surveys using indicator species and precise measurements using machines complement each other. One gives a broad picture, while the other provides specific details.
6. How You Can Observe Nature and Try This Yourself
If you want to try this yourself, start by observing the living things around you.
You can look at creatures near your home. With your family, try to find out what kinds of places pill bugs and ants prefer.
With an adult, you can go to a nearby river or pond. Turn over stones to look for insects. Be careful, as stones can be slippery. Always do this together with an adult.
It is helpful to write down one word that interests you. This can be a starting point for further research. For example, you might write: "When can we join the National Aquatic Organism Survey?" That is enough to begin your curiosity.