Observation is something we often do instinctively. Observation helps us decide whether it’s safe to cross the road and helps to determine if cupcakes are ready to come out of the oven. Observation is more than simply noticing something. It involves perception (becoming aware of something by means of the senses) and the recognition of the subject’s importance or significance. Standing on a roadside, our eyes tell us cars are quickly approaching. Prior knowledge warns us that stepping in front of a car is dangerous, so we wait until the road is clear.
Observation is essential in science. Scientists use observation to collect and record data, which enables them to construct and then test hypotheses and theories. Scientists observe in many ways – with their own senses or with tools such as microscopes, scanners or transmitters to extend their vision or hearing. These tools allow for more precise and accurate observations. Scientists also use equipment to measure things like radiation or pH – phenomena not directly observable.
Humans have been observing earthworms and their activities for a very long time. The Ancient Greek philosopher Aristotle referred to earthworms as “the intestines of the earth”. Charles Darwin is credited with inspiring popular and scientific interest in earthworms with his book The Formation of Vegetable Mould through the Action of Worms, with Observations on their Habits. Darwin kept pots of soil in his study so he could observe earthworms. He tested their sensitivity to light and heat, observed their food preferences and even set up challenges to test their intelligence!
Fast forward 50 years and observations of a more practical nature were taking place in New Zealand. A Raetihi farmer noticed that parts of his farm were more productive than others. He thought this was due to lumbricid earthworms living in some of his paddocks but absent in others, so he experimented by distributing earthworms around his farm. A few years later, scientists backed up the farmer’s observations and quantified the positive effects earthworms have on pastoral productivity.
Nature of science
Observations may be the catalyst to scientific investigations. The Raetihi farmer’s observation of his paddocks’ differing productivity levels led him to experiment by distributing earthworms around his farm.
Research into earthworm activity continues today. It is well known that earthworm burrows increase water infiltration and soil aeration and that earthworms have a major impact on nutrient cycling. Some questions remain though. Which species are present and where? How much do they eat? How are they affected by farm management practices?
To answer such questions, soil scientists Dr Nicole Schon from AgResearch and Dr Trish Fraser from Plant & Food Research use a number of techniques. To identify and quantify which species of earthworms live in an area, the most reliable method is hand sorting. This involves digging a cube of soil, sifting through it and counting the earthworms. The advantages of this method are its reliability and simplicity. The disadvantages are that it is time consuming and laborious and it destroys the burrows.
Earthworm burrows are difficult to observe but Trish has found a novel way to make non-destructive measurements of the burrows – computed axial tomography (CAT). CAT scans X-ray internal density. They are often used for medical reasons. However, Trish has scanned soil cores both with and without earthworms to observe physical changes in the soil structure. The burrows stay intact so Trish can observe how they develop and change with time. The downside is cost. CAT scans are expensive for humans and earthworms alike!
Scientists aren’t the only ones observing earthworms. Farmers and others use earthworms as a simple way to monitor soil health. Nicole has developed an identification guide that offers advice on when and how to sample for earthworms. Photos help the user to identify the earthworms from the soil samples. Different species provide different soil services (like organic matter incorporation or creating soil pores) so it is useful for farmers to know how many and what types of earthworms live in their soil.
For many students, one earthworm probably resembles the next as it struggles across the footpath on a rainy morning. Hopefully, this perception will change as students learn about how useful these creatures are to the soil ecosystem and spend some time observing their physical characteristics and movement!
Why not use one or more of these observation activities in your class.