Worm food investigation

Created Date:
Thu 29 October 2020

Last Edit Date:
Tue 17 November 2020

Students build a mini worm farm and investigate the factors that affect the rate worms consume food including the size of the food (large/small) and type of food (hard/soft). The initial lesson and investigation set up will take about one hour, with ongoing observations (10 minutes) twice a week over three weeks, followed by another full lesson to discuss final observations and write reports.

Learning objective

Students observe changes in the mini worm farm and record their information in a table format to show how the needs of the worms are met.

Curriculum links

Science: Science understanding

Biological sciences

Science as a human endeavour

Nature and development of science

Science: Science inquiry skills

Questioning and predicting
Planning and conducting
Evaluating

Cross-curriculum priority: Sustainability

Background information

Worm farms contain composting worms that eat food scraps and turn them into a natural liquid (worm leachate) and compost (castings) that can be used in the garden. Composting worms thrive in a moist, high nutrient environment and we create this environment in a worm farm.

Worm farms:

Decrease the amount of organic waste sent to landfill.
Close the recycling loop by changing food waste back into organic fertiliser for growing food.
Reduce greenhouse gases. In a well-maintained worm farm the decomposition process is aerobic (with oxygen), rather than anaerobic (without oxygen).

The earthworms used in worm farms are a different species to those we find in our garden. The best worms for worm farming are European worms such as the red wriggler (lumbricus rubellis) and the tiger worm (eisenia fetida). These species are accustomed to soils high in nutrients. They eat and breed much faster than other earthworms and can quickly transform food scraps into worm castings. They do this in a small amount of space, while other earthworms are better equipped for burrowing and searching for food in our drier, nutrient poor soils.

Worms are blind, but sensitive to light. Their instinct is to move away from light due to their two ‘photoreceptors’, which are sensitive nerve endings located near the saddle (Murphy, 2005).

Living conditions in a worm farm

Worm farms should be situated in a cool, shady spot. Worms need cool, moist conditions and a temperature of 25–26 degrees. They need a layer of bedding to live in which can include castings, shredded paper, newspaper, cardboard, brown leaves, and straw. As food scraps decompose, they will make the worm bedding more and more acidic, therefore it is a good idea to occasionally add some garden lime to maintain the pH as worms prefer a neutral environment.

School worm farms

A worm farm is made from a container that has a drainage hole for water and a lid that keeps out vermin but allows air in.

You can buy worm farm containers, make your own, or have one custom made. Some schools use old bathtubs but most use old fridges that have been safely degassed. Look at the ‘How to build a worm farm’ fact sheet to find out more. For most schools, at least one large worm farm (such as a fridge or a bathtub) is needed.

For information on what to feed a worm farm and what to keep out, please see the ‘Waste wise worm farming’ and ‘How to make a fridge worm farm’ fact sheets: www.wasteauthority.wa.gov.au/wws/teaching-resources/list/fact-sheets

Resources required

A two litre clear plastic drink bottle per pair (with the top cut off, see diagram)

Moist worm castings

Water

Compost worms

Newspaper

Large and small vegetable and fruit scraps

Hard and soft vegetable and fruit scraps chopped into similar sized long strips so that you can place them up against the edge of the bottle

Digital kitchen scales

Fork/mortar and pestle/blender (optional) for pureeing and a grater

Activity

To make a mini worm farm

Place about five centimetres of castings in each bottle and add a small handful of worms. Add about five centimetres more castings.
Carefully dig a small hole right next to the side of the container and bury one type of food item (large, small, hard, or soft) in the bottle. Make sure that you can see the food through the side of the bottle and that the food is completely covered with castings.
Add a small amount of water to moisten the worm farm. Wrap the outside of the bottle with a piece of newspaper and place a damp newspaper ‘plug’ on top.

Investigation instructions

Students will investigate why and how different foods break down in a mini worm farm. For example:
- What foods break down the fastest in a worm farm?
- How should food be prepared to optimise the amount of scraps that can be recycled in the school worm farm?
Which variables are relevant to worms eating food scraps?
- moisture
- temperature
- pH level
- quantities of food, worms, and castings.
Students discuss in pairs which variables should be changed and which should be kept constant.
In pair, students brainstorm different ways to prepare the food for example, pureeing, chopping, grating, or leaving food items whole.
Decide on a list of food items and ways to prepare these foods.
Identify possible hazards in this experiment and discuss any safety rules.
Each pair is given a food type and prepares the food accordingly. Students should use the same mass of food for each bottle and clearly label the food types in the mini worm farms.

Predictions

Students predict which food types will be consumed the fastest.

Observations

Students produce their own tables to record information on all the different food types.
Students monitor and record observations over a period of three weeks in the following ways:
- fill out their tables with their observations
- draw pictures and/or take photographs on the first day and then each week afterwards.